Intermittent PITA

I had another thread about this issue, but it was fuel system related. Well I've been through that and it's not the issue.

The Issue: Went driving along, everything is fine. When I'm at a red light (or my driveway) with the AC on, car in gear and idling with foot on brake, without warning, it'll hiccup and usually die really quick.

Car's back story, 70K when I bought it in March so it obviously sat for awhile. Guy I bought it from put 2K on it in 5 years, he got it from the estate of the original owner (old guy). I have put about 1500-1700 miles on it, 900 of those in the first week.

The AC compressor took a powder and after replacing all of that, it works great, but then the new issue popped up on Easter Sunday. It stalled at a light as mentioned above and wouldn't restart. Got it towed home and the next day it worked fine. Fuel pressure, etc all good, but as I have a 1K mile old pump and sending unit in the wrecked car, I swapped it over.

Car drives fine still but still stalling. Dug out my old PC and hooked up Datamaster and it was showing lean O2 on both banks and a EGR error. I pulled the EGR off the wreck and cleaned it up. Pulled the one off the Red car and it was stuck (yaaay I found it.....NOT), cleaned it up and it seemed to respond better than the known good one so I put it back on. Mistake. Realized today that it doesn't hold a vacuum so I swapped it with the good one from the 90K engine (wreck).

I cleared the codes and went for a ride. Second light and it did it again. Got back to the house and idled in the driveway where all of a sudden it idled like crap for like 4 minutes and then cleared up.

I read Mark Roady's issue with his MAP so I was watching that while it was running like crap and it didn't change values too much and stayed in the same area.

It is now only throwing the lean codes when it stalls (seems proper).

I know Jay said the coil and coil wire, that is next as my new Delco COil came yesterday...

Any other ideas?????

What about the ignition module? Not sure how reliable or not they are in these cars...

when it was idling bad, was it missing like cylinders weren't firing from poor ignition or from lack of fuel? would it rev if you hit the throttle?

You've got Datamaster (or eehack works great too)... monitor fuel trims to see if they're sitting around 128, look at Engine Coolant Temp (90-101C), MAP (should be around 30kPa at idle).  

I would datalog and note when the engine bogs down.  I'd also wonder if you have intermittent low fuel pressure and that's contributing to the lean codes?

Intermittent ICM or coil would not cause lean codes, IMHO.

sherlock9c1 wrote:

You've got Datamaster (or eehack works great too)... monitor fuel trims to see if they're sitting around 128, look at Engine Coolant Temp (90-101C), MAP (should be around 30kPa at idle).  

I would datalog and note when the engine bogs down.  I'd also wonder if you have intermittent low fuel pressure and that's contributing to the lean codes?

Intermittent ICM or coil would not cause lean codes, IMHO.

Had datamaster running and didn't notice anything but probably should record it and review it...

Fuel shouldn't be an issue as I just replaced the pump and sending unit and both the old one and the new one are in spec with pressure levels.

The fuel trim doesn't move out of 16 unless I throttle up.

When it was idling poorly, it didn't fell like a miss so much and giving it throttle it would smooth right out.

If it were a vacuum leak it wouldn't be intermittent, so that leaves spark IMHO. Going to change out the coil as I just got a new Delco unit in the maily

If you are on Facebook I just posted my datamaster run on my wall and on the bb wagon mafia page...

Wow Facebook is even worse than the forums for having a discussion like this.
What I'm able to see through the highly compressed video:

1. ECT is 193.6F which means it's good (unless it suddenly changes when the stumbling happens).
2. Closed Loop is enabled so the PCM should be responding to the O2 sensors.
3. Fuel trims are sitting at 160 so the PCM is adding max fuel.  What's the exhaust look and smell like?  Pull a few plugs - what do they look like?
4. O2 mV is sitting at L 36 and R 4 and not switching.  They should be switching between 0 and 900 mV.  Try plotting them in the display on the lower left corner.  
5. You say fuel pressure is constantly in the low 40s even when it's stumbling.

Do the O2 sensors start switching and the fuel trims drop down when you get on the throttle?  If so, I think the PCM may be going bad.  If not, you may have a wiring problem in the O2 sensors. Or the O2 sensors may be dead or shorted but I doubt it.  Or just try swapping another PCM from a car with the same injectors and intake setup and see if it'll run better.

Also check for rodent damage or chafing of the O2 sensor wiring. Rodents had just about eaten through the O2 sensor wires on one car I had.

Just looked at the video again. MAP is reading high at 50kPa (should be around 35); given what all the other parameters are showing, wonder if you have a vacuum leak.

Not a wagon or LT1 but my Honda CR-V had a problem where the engine would stall out when stopped or coming to a stop. Ended up being a massive vacuum leak, one of the hoses had dry-rotted and cracked lengthwise and the vacuum made it collapse in on itself basically.

THanks for all the info Joel and Rmaster King. It's been raining alot (lighting out right now), and went away for the holiday weekend. I agree I think it's a vacuum issue and will chase it this week.

What is interesting for a 70K car, what's been replaced (like a fresh Opti vent harness). I'm thinking the issue is probably why he sold the car as it's not an obvious issue. THere are a few other things, like the raditor shroud is brand new and the middle air dam is missing, the front bumper cover while the same color as the car looks like it came from another, so I figure something got run over with the front end...

Quote :

Wow Facebook is even worse than the forums for having a discussion like this.

There are no discussions on Facebook. You must be at peace while possibly talking to yourself while a lot of dogs are barking. Some on Facebook refer to this forum as "dead", because you might need to wait overnight for an intelligent answer, perhaps from only a single response, and with no mindless "likes".

"click"......Rant off.

based on the symptoms i would also suspect a vacuum issue.
i got a silicone hose kit for my lt1 and when my mechanic was doing the tuneup/optispark i had him replace the old hoses that i wasn't able to easily access.. Not a bad upgrade to do regardless - all those pretty blue hoses instead of boring stock black ones... makes people think you really care about the power plant

Does a vendor make a silicone vacuum hose kit for these cars? Or did you just buy the sizes and cut to fit?

I got mine as a kit but haven't seen any in quite some time - I actually was going to make up kits to sell for others complete with instructions but not sure if there's enough demand anymore for the LT1

AS I recall there were 20-30 different hoses, about 3 or 4 different sizes with a few that had two different sizes joined together with a fitting for a few of the replacement hoses

Depending on cost of something like that I would be interested, it would have to be black hoses so it still looked somewhat stock/original...

sherlock9c1 wrote:

Does a vendor make a silicone vacuum hose kit for these cars?  Or did you just buy the sizes and cut to fit?

I know ALex Bono (on FB) is having cooling hoses made. I'd be interested in some silicone vac lines!

Appears to have been a vacuum issue as suspected. I found the line from the driver's side PCV was VERY loose. Used a piece of heater hose to fashion a temp replacement as the set up was different on my 94. I also found a very bad hose off a thingy that attaches to Home Plate holder on the passenger side. I swapped it with the one on my 94 wreck and noticed that one was a spark plug cap!

Anyway it idled for over 15 min with the AC on no prob and then took it on a 10 min drive and seems ok now. FINALLY. Oh and it poured rain in the middle of me working on it lol

Glad to hear you finally got it sorted out.

Your in Fl right, doesn't it always rain at some point in the day!

rcktpwrd wrote:

Your in Fl right, doesn't it always rain at some point in the day!

Sometimes multiple times and the sun comes out and dries everything in between. lol

Rainy season is June-1/2 AUg, then it's the fat part of hurricane season until mid Oct

dmg4 wrote:

Quote :

Wow Facebook is even worse than the forums for having a discussion like this.

There are no discussions on Facebook.  You must be at peace while possibly talking to yourself while a lot of dogs are barking.   Some on Facebook refer to this forum as "dead", because you might need to wait overnight for an intelligent answer, perhaps from only a single response, and with no mindless "likes".  

"click"......Rant off.

You got that right. I took myself out of every group on FB. Too much nonsense and keyboard warriors. About to leave the whole darn thing because it has outlived it's usefulness.

So another issue was found and corrected. The plug on the water pump temp sensor was corroded so the reading to the computer kept changing and it would flip back and forth from open to closed loop and back again. This was causing the stall at the lights.

Ran fine for oh 5 miles and I shut it off, was REALLY hard to start again and now it doesn't start at all.
Looks like an issue with the fuel pump circuit as it will start and run if I jump the fuel pump under the hood. Once running is I take the jumper wire off, it still runs so I dunno what the hell else is wrong yet, but super frustrating.

As a recap:
New fuel pump, new sending unit, replaced EGR valve, replaced coil. fixed vaccum leaks and cleaned up corroded terminal.

Need to check the rest of the electrical connectors, and troubleshoot fuel circuit...

Between rain, cutting the crap out of my finger the other day (so don't want to get it greasy), and an upcoming road trip in the motorhome in 4 days.....it's gonna sit for a few more days

Hello Sprocket, interesting post did you finally get to the bottom of it, as I mentioned in my reply in the other post I too have to track down the lean burn on both banks issue.

My car seems to run very well, idles nice, no hesitation throttle is responsive, no stalling.

Other than a visual look for a vacuum leak, what should I be looking for? If I clear the code it won't come back on until I drive it for a while than restart and let it idle than the light comes back on.

I bought a new obII scanner but I really don't know what the parameters are supposed to be is there a list or chart that I can get to compare to?