Wierd engine issues

I have some, what seem to be related, issues with my LO5.

1. When stopping at a light, the engine will idle at 1000-1100 RPM, and slowly settle to 750 RPM. Sometimes it will just idle at 750 RPM when I stop.

2. When starting after sitting 10-30 minutes, the engine will quit, or bog when given judicious amounts of throttle, then clear up, and run fine.

3. The engine will intermittently bog after idling at a light, and then clear and run fine.

4. It does not throw any codes now, although I had the fuel pressure set too high initially and it did throw some rich codes.

I have changed the IAC, TPS, IAT, coil, and has a new cap, rotor, wires, plugs and good ignition control module. I put in a new fuel pressure valve membrane, set the adjustable fuel pressure regulator to 1/16 inch higher than the original position. The injectors are 9C1, cam is LT1, TBI is oversized (BBC). I have tested the cable for binding. I also changed the fuel pump relay. None of this affected it in any noticeable way. It did similar things except for the high idle when stopping before I swapped engines.

I have not changed the MAP, or checked the plugs. I have a fuel pressure gauge, but I can not read it while driving. I think it shows 10.5 PSI, and it does not appear to change, no matter how I adjust the fuel pressure regulator.

I am considering swapping the fuel pump. I currenty have an AC Delco pump. Does anyone know anything about Delphi, or Denso pumps? I have a new Bosch pump laying around, but am fearful of installing it because of my past experiences with Bosch. I also just filled the tank, so nothing will happen with the pump until I get down to about 1/8 or less in the tank. Advanced Auto Parts has a 30% off sale this weekend, and I would like to take advantage of it if possible. I am on a tight budget.

Fred Kiehl wrote:

I have some, what seem to be related, issues with my LO5.

1. When stopping at a light, the engine will idle at 1000-1100 RPM, and slowly settle to 750 RPM. Sometimes it will just idle at 750 RPM when I stop.

2. When starting after sitting 10-30 minutes, the engine will quit, or bog when given judicious amounts of throttle, then clear up, and run fine.

These sound like the traditional hallmarks of a lean idle condition -- 1. is known as a "hanging idle" (a rich idle will usually show the exact opposite -- engine will almost die as it comes down to idle, then recover). 2. happens in that first moment of air inrush leaning out an already lean mixture before the system can compensate.

Quote :

3. The engine will intermittently bog after idling at a light, and then clear and run fine.

I'm not sure exactly what you are describing here. Do you mean it bogs while idling? As you come off idle (like #2) or that it comes off idle OK, then bogs?

Do you have a scan tool, so you can monitor the live data feed? Even though you changed various sensors, it may be worthwhile to look at how the ECU is interpreting the values it receives. A bit of corrosion on a connector, an intermittent ground, a bad sensor, etc. could be misleading the ECU. It is also worthwhile to look at the fuel trim values. If they are at the extreme limit of the range, then the system is trying to correct for something beyond it's ability to do so. And, if available on the L05, the fuel trim block number might provide a clue. Does it change as expected when you take off from the light?

I do not have a scan tool. Most of the time, when it is in closed loop, it will just hiccup when I first touch the gas pedal. Then it catches and takes off. Just recently it decided to have an episode of not having much power until it hit about 20 mph. I also found the intake tube for the cold air worked its way out of one of the clamps. I reattached it today, and it seems to be back to just a little hiccup. The main issue is the start and quit, then run poorly for about 30-45 seconds when restarted hot. It did this with the LO3, before I changed to the LO5. I do not remember the hiccup with the LO3. With the LO5, the hiccup was there when I was running the fuel pressure too high, and did not go away when I lowered the pressure setting. The current setting is like having a quarter under the spring.

Fred Kiehl wrote:

I do not have a scan tool.

This is problem number 1. Go get yourself a scan tool. Monitoring and data logging have been invaluable towards diagnosis in my experience.

I am glad you can afford to just go get what you need. I do not have the funds right now. I believe I am going to try the fuel pump. The issue that bothers me most is the poor hot start, and poor running for a short period after that. Since that occurred on both engines, and the only sensor I have not changed is the MAF, I suspect the fuel pump more than anything else. With a fuel pressure reading that I suspect is low, the lean conditions you mentioned that would cause the transition issue would also be likely.

Fred:

Cross out the two upper right hand terminals in the data port. If you look closely, they are the only terminals with metal in them, adjacent to each other. Your L05s are OBD1 and are not flashable so this method works.

With both terminals crossed out turn the key to on (not start) and watch the CEL light closely. It will start to flash a sequence immediately. The first sequence will be flash...pause...flash flash. This equates into code 12 (means you have crossed out the terminals correctly). It will repeat this sequence 3 times. At this point it will move to the next code and repeat it 3 times then on to the next code, each one repeating 3 times for slow writers. When it returns to 12, you have gotten all the codes.

No need for a code reader.

Bill

I have done that, and there are no codes.

Fred Kiehl wrote:

I am glad you can afford to just go get what you need. I do not have the funds right now. I believe I am going to try the fuel pump. The issue that bothers me most is the poor hot start, and poor running for a short period after that. Since that occurred on both engines, and the only sensor I have not changed is the MAF, I suspect the fuel pump more than anything else. With a fuel pressure reading that I suspect is low, the lean conditions you mentioned that would cause the transition issue would also be likely.

Fred, I deeply sympathize with your lack of funds, and maybe a scan tool just isn't affordable right now. However, long-term, a scan tool is a money (and time) saver. You can pick up a decent used OTC or Matco 4000E on eBay for under $200. Here's [You must be registered and logged in to see this link.] (picture is a bit fuzzy so I can't tell for sure if it has the right cartridge -- you want the Pathfinder95 or Pathfinder97, it has PathfinderII but that's too old for these cars and I can't make out the other cartridge. It does have the right cable. [You must be registered and logged in to see this link.] -- even includes cables, cartridge and inserts for OBDII cars up to 2001. Starting bid $125, BIN $175. I have the Matco-branded version of this tool and it has served me well over the years. An immediate use would be to check the MAP value with the Key On, Engine Off, then Key On Engine Running to see if the correct values are being received by the ECU. You can compare a vacuum gauge reading to the displayed value (after converting vacuum to absolute pressure, of course).

I know you tinkered with the fuel pressure regulator, but did you ever actually swap that out? Can you get an assistant to read your fuel pressure gauge while you drive? I'm wondering if the regulator could be a bit sticky. As you undoubtedly know, it dumps excess fuel back to the tank. If it stuck in position at idle, it might be dumping too much as you accelerate, causing a temporary lean condition. It could even explain the hanging idle, since the engine probably uses less fuel when decellerating to a stop than it requires when actually idling. If your assistant sees a drop in pressure below 9psi when the engine bogs, and then the pressure returns to normal when the engine recovers, it would confirm that suspicion.

With regards to the fuel pump: This may seem a bit counter-intuitive, but it takes relatively little energy on the part of the fuel pump to develop static pressure -- that is, pressure without flow. It takes a lot more energy to develop less pressure at full flow. So a failing fuel pump most often manifests itself when engine rpms are higher, not at idle. The correct range of pressure for the TBI system is 9 to 13 psi, and you are in that band, so I really don't think the sum of your symptoms add up to a fuel pump issue. All that said, with your infamous stock of spare parts, perhaps a fuel pump swap is a cheap diagnostic in your particular case.

I may throw a different MAP sensor on just to compare the two. I listed rebuilding (replacing the membrane) in the fuel pressure regulator as one of the "fixes" I tried. The regulator bowl has an adjustable screw on the bottom, but the casting is one I picked off of my shelf. The odd part is that the pressure reading on the gauge does not appear to change, no matter how I have the regulator adjusted. I have tested the gauge, and it will read correctly at higher pressures. I may try swapping regulators to a stock one for comparison's sake.

Having an assistant read the pressure while I drive would entitle having the hood open, and the assistant hanging onto the outside of the car. I personally do not know anyone who is willing to do that. I guess I could plumb a temporary line to allow the gauge to be visible while driving.

Fred Kiehl wrote:

Having an assistant read the pressure while I drive would entitle having the hood open, and the assistant hanging onto the outside of the car. I personally do not know anyone who is willing to do that. I guess I could plumb a temporary line to allow the gauge to be visible while driving.

Your gauge hose must be shorter than mine. I have enough to set it on the windshield with the hood closed. I'd be perfectly happy to loan you a kid stupid enough to try it your way.   Alternatively, it may not be necessary to actually move the car. I wonder if putting it in drive with your left foot firmly on the brake would apply a sufficient load to simulate pulling away from a stop while you hit the gas with your right?

Fred, when I was having hot restart issues it was because of the Ignition Module.  It gets heat soaked from the engine after it gets turned off.

I solved the problem by  cutting the wires in the distibutor from the  magnetic trigger to the module,  then extending the wires to the new mounting place of the module. In my case i moved it to a flat spot on the fender well. I sandwiched it between a flat late of aluminum as a base,  (screwed to the fender) and a finned computer heat sink on top. Haven't had any heat soak issues since. Two thick  (1/8-1/4') plates would likely work just as well. I happened to have a computer fix it shop nearby, and the heat sinks were only a couple bucks from his scrap pile.  You just need something to suck the heat away to the fender, and point the connections towards the firewall so you don't get rain driven into them.

Don't mount it on the firewall above  the headers. It's too hot there as well. Get it out into the airflow.t's best to take three wires twisted together to help eliminate spurious RF signals messing up  the module signal. The third wire gets grounded on the fender (body) or nearby chassis ground, NOT to the engine. Although I put a fan on it. It has proved unnecessary. Obviously, You might need to extend the other wires to get there as well. Soldered connections  with heat shrink tubing will work better than crimped ones.

It's a cheap fix.

Dave

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Dave

Interesting fix. I may try it. That is one problem that followed from one engine to the other. It could also affect the idle issue.

This is what I would be looking for as a potential issue. Common problem with these units. When you swapped engines did you reuse the distributor from the other engine? This would explain the issue following the the new engine, if you did. Even if you didn't, look anyway, as stated this is a common issue. If this is the case I would install a new distributor. Brand new they aren't real expensive and are drop in ready. New cap, rotor, ignition module, pickup coil, distributor shaft and housing. Seen one on Rock Auto for around $85 with no core plus shipping.

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Thanks for the photo. That should help a bunch of us in terms of what to look for.

What are the symptoms of the cracked magnet?

Fred Kiehl wrote:

What are the symptoms of the cracked magnet?

It depends where and how many cracks. The reluctor is supposed to provide evenly spaced spikes in the magnetic field. Cracks in the magnet add or subtract from those spikes, or may even add entirely new spikes. So misfire, strange timing issues, premature cap/rotor failure or other ignition problems may occur.

Another possibility that comes to mind is a loose pickup coil assembly. I ran into that one time on a similar (91 Chev K1500) engine with a strange variable idle. It had the effect of randomly varying the timing as it rotated back and forth.

Fred Kiehl wrote:

What are the symptoms of the cracked magnet?

Let's see here, erratic idle, stalling, no start, unstable timing, hesitation, etc...

gmtech wrote:

Fred Kiehl wrote:

What are the symptoms of the cracked magnet?

Let's see here, erratic idle, stalling, no start, unstable timing, hesitation, etc...

You would expect severe symptoms of all of those at all times. The issues I have are under certain conditions. It does not have erratic idle, it just idles high when I come to a stop, and settles to a correct idle over a minute or so. It does start every time. It does not stall generally, only when I have a hot start with heat soak, and clears up in less than a minute. The timing is stable when excellerating, and idling. The engine pulls hard. When excellerating from one speed to another, there is no hesitation. It generally does not hesitate unless it is stopped, at idle, in closed loop, and I press the gas pedal. I believe the chances of having a cracked rotor would require it to have far more severe symptoms than I have.

Fred Kiehl wrote:

gmtech wrote:

Fred Kiehl wrote:

What are the symptoms of the cracked magnet?

Let's see here, erratic idle, stalling, no start, unstable timing, hesitation, etc...

You would expect severe symptoms of all of those at all times. The issues I have are under certain conditions. It does not have erratic idle, it just idles high when I come to a stop, and settles to a correct idle over a minute or so. It does start every time. It does not stall generally, only when I have a hot start with heat soak, and clears up in less than a minute. The timing is stable when excellerating, and idling. The engine pulls hard. When excellerating from one speed to another, there is no hesitation. It generally does not hesitate unless it is stopped, at idle, in closed loop, and I press the gas pedal. I believe the chances of having a cracked rotor would require it to have far more severe symptoms than I have.

Have you even looked to see if the magnet is cracked or do you want to continue your diagnostics in the same fashion you have to date? A look doesn't cost as much as installing parts that don't fix it. I'll remain silent and watch how this turns out. Good luck in your quest for a valid repair. Sorry I'm unable to help you.

I have not had the opportunity to look, but I will. I am open to what ever will fix the issue. It will probably be somewhat low on the list, because the symptoms are markedly different from those described for the problem. I am not sure if the distributor is the same one that was on the original engine. I believe I used the distributor that came with the donor engine, because it had less than half the mileage.

Fred when you stomp the gas do you hear the fuel pump rev up really loudly? Does the time to start when it's been sitting for over 6 hours take about a second or two longer than normal? I had a pump go bad on me last year, that exhibited the same problems with stumbling idle, hard acceleration stumbling, and starting the car approximately 30 minutes after I shut it off, only to have it stumble and die. Giving it gas resulted in it running rough (sporadic idle) for a few seconds, up to a minute, until it started to normal out the idle. I rented one of them fuel pressure tester and found that the fuel pump would provide adequate fuel pressure when running, however when I shut it off the pressure in the line would drop to 0 so fast I thought I was seeing things. I know there's some leak down in the fuel lines but dang it hit 0 in less than 2 seconds. I deduced that the leak down valve in the pump was bad, replaced the fuel pump and problem was gone. I'm not saying this is whats going on with your wagon, just what I experienced with mine.

Oh and I noticed that you mentioned you weren't getting any codes I just wanted to mention the General Motors Field Service Mode procedure. It's a simple test to determine how the engine is running (i.e. Open Loop, Closed Loop, Lean Exhaust, Rich Exhaust). I stole it from the inter-web    

General Motors Field Service Mode
You are out in the middle of nowhere without any tools. Here's an easy test that can be performed on any General Motors fuel-injected vehicle for 1982 until 1995(1992 on some models). All you need is a jumper wire or paper clip! Whether the engine is in closed loop or open loop, a rich or lean condition can easily be determined by connecting terminals A and B in the 12-pin DLC and starting the engine. (This test is not available on vehicles equipped with the 16-pin OBD ll connector.) Check the operation of the "check engine" lamp (MIL). With the engine running and the diagnostic terminal B grounded (DLC terminal A connected to B), the "check engine" lamp should be off when the exhaust is lean and on when it is rich. The procedure is called the field service mode.
l. Open loop. "Check engine" lamp flashes at a rapid rate of two times per second.
2. Closed loop. "Check engine" lamp flashes at a slower rate of one time per second.
3, Lean exhaust "Check engine" lamp is out all or most of the time.
4. Rich exhaust "Check engine" lamp is on all or most of the time

Fred,-

Nobody is right 100% of the time, and diagnosing via the internet is highly dependent on one person clearly understanding what another person is attempting to describe. That's even assuming the party on the other end of the line is not just another "internet guru", so it's always prudent to carefully weigh the value of any advice received.

That all said, gmtech is a professional mechanic with a fair bit of knowledge and experience, so any advice he has should be weighed accordingly.

Given that these cars are ~20 years old, it is even possible that you have more than one problem contributing to your collection of symptoms. The exact symptoms of a cracked magnet may vary somewhat from car to car (eg: heat may expand the magnet, so the effects of a crack in that magnet may also be heat dependent). gmtech may well be barking up the wrong tree, but it won't cost you anything to find out. Personally, given the circumstances, the ease and cost of looking at the magnet and the source of the suggestion, I'd move that one up the priority list a bit.

I'd have to agree with Mr GMtech on this one Fred. It won't hurt to look before throwing cash at it.
Lords knows I haven't always taken that advice on Shammoo. It would have saved time money and aggravation.

If you no other reason, you'll need to pull the rotor off anyway to replace the distributor . A little magnifying mirror and light might help keep you from needing to pull it all the out, if it can be eliminated from being the cause.

Dave

I still have a few issues to deal with in the car other than the engine issues. I had a fuse melt in the main fuse block. It is actually the second one, so I am changing the fuse block and splicing new connectors in the melted sockets. The clips that hold the fuses overheated on the battery side, probably due to poor contact/connection.

The car is generally drivable, and I will get around to further troubleshooting when I get the fuse block done.

Good luck and as always, best wishes.

Dave

I had a talk with my local mechanic, and he thought it might be a vacuum leak. I decided to retorque the intake manifold bolts, and found that the vacuum line to the brake booster was very loose. I tightened it, and most of the issues went away. I still have a hesitation when I transition from idle to power, but it may be the idle adjustment on the TBI. I also have an intermittent miss, which may be a bad plug or two. At least I solved one issue, and as I work on it the others will come around. I may even reset the valve lash, just for grins.

It turned out to be a leaking throttle valve shaft, and poorly performing fuel pump. When there are two problems, it is difficult to diagnose, because they can affect each other, and look like a totally different problem. I replaced the TBI base (46mm) with a rebuilt one, and installed a new fuel pump. Now it feels like it has more power. The idle is about 600-700 RPM, and it no longer stumbles at launch. It was definitely a fuel/air issue. I soldered the pump wires at both ends, and doubled the hot side wire. I also found the easy way to install the tank when I am doing it alone with the car on jackstands. I put the straps on at the rear and slid the tank on the straps from under the axle. Then I lifted it with a floor jack at the front of the tank...bolts went right in...done.  I am down to a small intermittent glitch when the compressor kicks on...relay?.

I also found that I had an aftermarket sender unit in the tank, and when it turned the low gas light/chime on I still had about 8 gallons of gas in the tank. I had to syphon most of it out. I installed a slightly modified OEM sender unit. It read about 1/3 of a tank with the gas back in the tank.

Thanks for all the ideas. Some worked, some were a little frivolous. I am finally getting happy with the way the car drives.

Good to hear Fred,bet it feels good to stomp it now.TBI comments to follow!

Congratulations on solving the problem.

Fred Kiehl wrote:

I ... set the adjustable fuel pressure regulator to 1/16 inch higher than the original position. The injectors are 9C1, cam is LT1, TBI is oversized (BBC).

It is worth noting that if you have not had the engine computer adjusted for these alterations, the engine will never run as good as a factory stock calibration with factory stock equipment.

sherlock9c1 wrote:

Congratulations on solving the problem.

Fred Kiehl wrote:

I ... set the adjustable fuel pressure regulator to 1/16 inch higher than the original position. The injectors are 9C1, cam is LT1, TBI is oversized (BBC).

 It is worth noting that if you have not had the engine computer adjusted for these alterations, the engine will never run as good as a factory stock calibration with factory stock equipment.  

LO5 engine computers can not be adjusted for the above alterations. I do have a custom chip in the computer.

I think you're saying that you adjusted the calibration? Does the calibration match the mods? I don't mean to pick at this so much, but this has bitten me in the past. I once had a situation where the engine was modified AND the calibration was modified and they didn't match. I ended up having to put together a custom calibration for it that took a lot of time, since the particular engine combination was not common.

The point is, situations like this can very likely cause drivability issues that will have you pulling your hair out to figure out the cause, but will never be obvious unless you know to look for them.

I write this not to poke you in the eye, but for anyone down the road who ends up reading this thread trying to solve a drivability problem - check the calibration and see if it matches the engine.

Joel, yoou are correct that  changes can adversely affect things, and Fred is also correct that Two problems can mask themselves as a third problem.

It took a long time to get Shammoo running reasonably ( note I didn't say well or properly) The more things are changed the less likely the stock calibration will suffice.. Just as I read Fred's comment in an earlier post, I was thinking that that he'd need changing  of the Acceleration Enrichment  (AE) tables, that is until he reported a vacuum leak as the problem.

Dave

PS I hope you enjoy Huntsville. Sorry to see you leave the area here.

I bought the package with a chip in the computer that was supposed to be designed for the parts I installed. It ended up having a worn out TBI body, but I installed the parts from the package. The fuel pump issue was already present. The fact that the hot start issue stayed with the car when I replaced the engine led me to the conclusion that part of the problem was the pump. When my mechanic suggested that the idle issue was caused by a vacuum problem, I found the loose brake booster line. When it semi cured the idle issue, I looked for more vacuum leaks, and found the wobbly shaft in the TBI body. It took a while to let the symptoms sink in and process them. As each item was fixed, the others became more apparent. I may have a little more tweaking to do yet, but my first instinct that it was a mixture issue proved out.

I know moneys tight but,.....[You must be registered and logged in to see this link.]

No guessing

The tester you referred me to can not be used on an LO3/5 to check fuel pressure, because there is no place to hook it to. I have a fuel pressure gauge permanently installed. The gauge showed enough pressure, but fluctuated under some conditions. The vacuum aspect of the gauge checks for vacuum manifold leaks (as in the rubber/plastic hoses, not a leak such as the ones I had). The vacuum issues were independent leaks, not part of a manifold. One of them I did not expect, because I thought I had tightened the fitting. The only way to find the type of leaks I had, is to squirt water or brake cleaner on the suspected area, or make an observation that would identify a loose or ill fitting part. I found a loose part, and a worn part.  I have a leak/pressure tester like the one from HF, and it was not useful in this case.

Fred Kiehl wrote:

The only way to find the type of leaks I had, is to squirt water or brake cleaner on the suspected area, or make an observation that would identify a loose or ill fitting part.

Another good way is to use an unlit propane torch. When it finds a vacuum leak, the propane richens the mixture.

Don't try this if you have or suspect arcing ignition wires though.

Water with a couple drops of dish washing liquid is the safest, and works as well as any flammable.

Fred Kiehl wrote:

Water with a couple drops of dish washing liquid is the safest, and works as well as any flammable.

I don't think so,. good for 'pressure' leaks,. not so good for 'vacuum' leaks, But you know best.

I have used it to check vacuum leaks, and the vacuum will suck it in with a audible sound.

Fred Kiehl wrote:

I have used it to check vacuum leaks, and the vacuum will suck it in with a audible sound.

sounds like a toilet flushing right?

Kinda more like my wife snoring, but only several of you would know that.

More like when you suck through a straw at the bottom of an almost empty glass.

The final issue is solved. I replaced the O2 sensor. All is good.

Congrats.

I had the car over at my preferred mechanic last week, and while he was doing a little "fix" to the jack pads in the rear, I found one little item that can still affect the engine running and especially the idle. The vent line for the gas tank is cracked, and leaks gas when the tank is full (I just filled the tank or I would not have found it). Consequently, it would also leak pressure when the tank is not full, and cause a fluctuation in fuel pressure, thereby causing the idle to be unstable. Looks like I am going to be lowering the tank again. I hope I can only partially lower it to replace the hose. It gets frustrating, but the end is in sight.