Fuel pump, Pressure regulator, or look elsewhere for problems?

My OCC has cranked longer than I think it should for the whole year I've had it..... Yesterday, I twice cranked it up about fifteen minutes after having drove it 10 or so miles, and the thing surged and stuttered as if it wanted to stall for the first three minutes it ran, and then cleared up and ran normal....
Today, I got a fuel pressure test gauge teed in and see it doing a pre-prime of seven psi and the engine runs 9-9.5 psi fuel pressure.... I can't find specs, but think I've read that the fuel pump is supposed to provide 13-18 psi (?) The pressure falls almost immediately after the pump electricity shuts off.
I've been advised to check the pressure regulator by crimping the return hose with vicegrips, but I'm afraid to do so because the hoses on the return line are those hard plastic teflon lined hoses that I'm sure I'll ruin if I try to crimp.....
I'm thinking that my next step is to replace either the fuel pump or the TBI ( to assure replacement of the regulator)
Any suggestions?

A new fuel filter,.

stretch the spring to raise fuel pressure,.

Already did a filter.... I'm thinkin 9psi is low... Adjustable regulator on ebay for $50.... Hmmm...

AzDon wrote:

Already did a filter.... I'm thinkin 9psi is low... Adjustable regulator on ebay for $50.... Hmmm...

stretch the spring for free,.or buy some service parts,.

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did you do the filter before or after the problem,.?
i know some tbi trucks the fuel filter has a drainback valve in it,.on other cars the fuel pump itself has the foot valve in it,.

Nick

I've got a 93 RMW 5.7L TBI which I think takes longer to start than normal too. funny thing is if I drive it and let it sit for less than 2 hours then it cranks right up fast like. If it sits longer than 2 hours it takes a long time to start (3-4 seconds). I haven't tried troubleshooting this yet so this might not be much help but. . .

I remember reading somewhere that these cars have a redundancy system that if the fuel pump relay goes bad that they will still start when the oil pressure builds in the engine,(hence the long crank). I think when the relay goes bad you won't hear the pump pressurize when you turn the key to on, because it aint.

Plus there's a fuel hose in the tank that goes from the pump to the thing-a-ma-jigger (technical term) coming out of the top of the tank that can split and cause fuel pressure to drop.

I'm thinking my problem is the relay but like I said I haven't taken the time to troubleshoot it yet. I have the manuals and all just not the time right now, and it is still starting.
my guess is your problem might be related to the in tank fuel line, cheaper than a fuel pump. But if you're dropping the tank might as well replace them both right?

I have a similar problem with my '93 RMW , although it starts easily, just runs like crap until warmed up....then it is fine. Always thought if it was fuel pressure related, it would run worse at higher RPM's?

Fuel pressure spec on the TBI engine is 9-14 psi, but that is not the end of the story. The fuel pump also needs to keep up the volume to meet the fuel needs of the engine.

An extended crank could mean several things and not necessarily a fuel pump issue. Although, it could be part of the equation. If the check valve in the fuel pump is not holding a residual pressure in the fuel supply side of the fuel system an extended crank could result due to drain back into the fuel tank. The 2 second f/p prime when you cycle the key on will not be able to fill the entire fuel supply line and result in the extended crank. Check for fuel pressure to drop off when turning the key off, should be fairly steady and drop slightly. If it drops to zero a likely cause could be the check valve in the fuel pump. But do not forget the fuel pressure regulator could be bleeding fuel pressure off too. (It could be the reason for a low fuel pressure reading, 9.0 psi)

You may also need to perform a fuel volume test to check the integrity of the fuel pump ability to move fuel. Fuel pump only moves fuel, pressure is created by a restriction in the system, i.e. fuel pressure regulator or other restrictions in the system. The volume spec I generally look for is about 1 pint in 15 seconds or less.

Do not forget there are other things that can cause an extended crank. A weak ignition system can create the same type of concern. Plugs, wires, cap, rotor, ignition coil, pickup coil, etc.... High resistance in any one of these components can tax the ignition coil to it's limits and then minimize the actual burn time at the spark plug. Look for a reluctor (timer core) magnet cracking, in the distributor, under the rotor. If cracked, replace it along with the pickup coil.

Hope this helps you out. Good luck.

One of my pet peeves is the hose that connects the fuel pump to the fuel line in the tank. They are subject to cracking. It will act a lot like what you are describing. If the crack is small, the torque of the motor may keep it closed when it has been warmed up, or it may open it. It can vary the amount of pressure depending on whether/how far the crack is open or closed, just like a relief valve. Another symptom was a fluctuating idle. It was extremely hard to diagnose, and took me about 3 months to figure it out (before I knew about the Forums). The main reason I took so long, is that I did not want to drop the tank. It was the last possible cause of the problem, when it should have been the first item examined.

The engine needs 9 psi to idle properly, and usually needs about 15 psi when running. The pressure will be low if the pump can not meet the volume the engine wants. I have had both the check valve fail, and the hose crack. It happened on the same car within 60 days of repairing the hose. The original pump lasted 30 days, and failed, then the new pump decided not to hold pressure at the check valve (do not buy a Bosch pump).

In the interest of not dropping the tank unnecessarily, I decided to check the pressure on the fuel line while isolated from the pressure regulator (disconnected from the TBI) meaning that I'd only be able to analyze the pre-prime.
This test showed that the pre-prime is only seven pounds, but it also revealed that the pump is able to hold that pressure almost indefinitely after being shut off.
I have just recieved a new pump from Rock Auto, but I'm thinking that the pressure regulator needs some work also

The regulator is pretty easy to rebuild. It can be done in about a half hour, if the engine is cold.

I would check the pressure after swapping the pump, before you rebuild the regulator. You may find out that the regulator is just fine. You checked the pressure before, and without the regulator. Since it was only getting 7 psi the pump is regulating the pressure before it ever gets to the regulator. If the line pressure is less than the regulator's minimum, the regulator is only sitting there looking pretty. The actual pressure should be 15-18 psi even with just the prime. The regulator is supposed to keep the pressure steady at 15-18 psi at all times. The low end of 9 psi is the minimum it will idle reliably, and not indicitave of the pressure that should be present.

You could always deadhead the fuel pump to get max pressure, you should see in excess of 60 psi, even out of the low pressure TBI pump. Pressure is not about the flow, it's about the restriction. Deadheading the fuel pump may cause the rubber hose in the tank to come apart (it was going to anyhow).

I've had fuel pumps with great pressure all the way through the operating range, but not have enough volume to keep up with the engine needs. Fuel pressure is not a good indicator of fuel volume.

Here's what is: If you have a scan tool drive the vehicle and observe the O2 sensor voltage, make sure engine is in closed loop. Go WOT and observe O2 sensor readings, readings should go rich (900mV or more) if the fuel pump is working with good volume. If the O2 sensor voltage drops to less than 100mV during WOT, you are running extremely lean and the fuel pump cannot keep up with engine demands. (Dirty filter could also cause this lean condition. I read you have already replaced yours, so it is ruled out.)

Yeah, I know engine management ignores the O2 sensor for fuel control at WOT and therefore sends it into open loop, but it is still reading the O2 content of the exhaust stream. It's the best indicator of fuel delivery to the engine.

Of course, some of this information leads to fuel pump replacement, but double check the power and grounds on the fuel pump circuit with the tried and true voltage drop test. This test finds any excessive resistance that might be lurking in the wiring to the fuel pump. If you have to drop the tank make sure the pass-thru connector on the sending unit is not overheated/melted. This is often over looked and requires dropping the tank a second time shortly after original replacement.

Well.... I've now replaced the pump. Against the regulator, it shows 10psi preprime and 10psi running and the pressure falls quickly when the pump is shut down. Tomorrow, I'll check isolated fuel pressure (with the regulator excluded)
After that, I need to drop the tank again because now the fuel gauge is showing 1/4 tank more fuel than I poured back in it. I was VERY careful orienting the filter sock, but there's no way to tell if everything is placed properly inside the tank. I guess next time I'll plug the harness into the empty tank and check the gauge before installing the tank (after pulling the fuel relay so the pump doesnt run dry)
I took lotsa pictures to detail the surge tube that must be removed to get the gas out and also, what SHOULD BE the proper orientation of the pump sock to assure proper fuel float travel...

The pump sock should be side to side, and I think the long end goes to the driver's side. You may have knocked the float arm loose from the clip, or have it caught under the clip. The pump sock should not even be near the float. The float should point toward the rear of the car.

It is not unusual for the pressure to bleed off after the pump is shut off. 10psi sounds a little low. You might want to have you fuel pressure gauge calibrated, or check it against another car, to be sure it is correct.

Does it run better since you put the pump in?

The pump sock IS left to right and I was VERY careful to be sure that it went in the direction where it had the space it needs to lay flat (to the right)
I'm not really sure yet if it runs better......

AzDon wrote:

I'm not really sure yet if it runs better......

It,s like that with all TBI cars,.

What brand pump did you buy?

If you choose to rebuild the regulator, it is easy to rebuild. The kit spring may be shorter than the OEM part. The instructions that come with the kit say to be extremely careful with the spring. I have taken a couple apart, the the spring is really wimpy. You can remove the retainer with your fingers. Just hold on to it, and it will not shoot across the room. I used my thumb to hold it down, and slowly released it. The total travel was about 1 inch. I reassembled it with my thumb too. The posts they give you to guide retainer on, make it easier, but you can do it without them if you are very careful (use the guides, it is easier). It took me longer to get the unit off of the car than to rebuild it. The old gasket will probably break, and stick to the surfaces. Make sure the gasket surfaces are clean, before reinstalling the regulator with the new gaskets provided in the kit.

Fred gets it right... I'd knocked the float arm out of the reostat clip and had actually broken one of the clip fingers (drat!) The thickness of the ziptie I used to fix it now prevents readings below 1/8 tank (I'll live with it!)
Pressure excluding the regulator holds at 20 psi indefinitely. With the regulator, runs at 10psi and doesnt hold it when shut off.
Up next: regulator work!
Oh, I bought the "Performance Electric Fuel Pump" from Rock Auto that comes with the fuel sock. The Packaging implies that it's manufactured in Sugarland, Texas, but I'm bettin it's Chinese!
I'm not gonna run it any more till I pour another (at least) 5 gallons of gas in it....

You should never run less than a fourth of a tank anyway. You have to remember that one eigth of a tank is effectively empty. You could pull you gauge pointer, and move it to where it shows empty at one eigth of a tank.

You may not be at fault. The clips break easily after many years submerged in gasoline. The alcohol in today's gas tends to accelerate the process too. I have one with a broken arm which I am going to try to fix.

I have the plastic float arm. You have to be really, really, really good a fixing things to replace it. The body of the sender is heat welded onto the flange on the rod, and there are ears bent over the top of it as well. First bend the tabs up, then if you can heat the welds to soften the plastic and pull the pins out, you can remove the body, and replace the arm.

Reassembly is the reverse, except you have to heat the pins, and flare them after inserting, to keep the sender body from falling off. Another option is to drill and tap holes in the plastic, and use small bolts with lock nuts to reattach the body of the sender.

Rockauto is peddling new sending units for our wagons with everything but the pump pretty cheap:

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jimbeau wrote:

Rockauto is peddling new sending units for our wagons with everything but the pump pretty cheap:

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$122 plus shipping is not exactly cheap. They only have one left as well.

I almost never run a fuel injected car below 1/2 tank anyway, but I DO want to know that the gas gauge is reliable down to below a quarter.... If it never goes below half, I might forget to fill up!

It would still be reliable below a quarter, because empty would be one eigth.

Hey, it includes a brand new fuel sending rheostat, new fuel lines; the whole schmeer.
I'm just grateful that we can still buy this stuff new, rather than cobbling JY stuff.

UPDATE!--
I bought a TBI rebuild kit that includes a new spring from carbdoc on ebay.... Their spring actually LOWERED the fuel pressure!
Next, I bought an adjustable housing from ebay that includes a 15 psi spring..... Installed it provides 13psi of fuel pressure....GOOD ENOUGH!

What I discovered as I was installing the new stuff was that the original housing's adjustment screw was soldered in a position with the spring pocket fully retracted, so none of the springs were long enough in that housing to provide enough pressure!
I now have several extra springs and a stock housing that I can feel free to modify for adjustability.

Back in the heyday of TBI I toured the Rochester Products plant in NY, '85-'86 era. The solder you speak of was actually a weld, and when I asked why they were doing that, the response was so the regulator can't be adjusted. Of course, this time frame represented the early stages of "new technology", electronic fuel injection. I was still working on carburetors then and this new fangled technology was interesting to me, therefore the question. The plant was still producing carburetors at the time and getting ready to transition over to TBI.

HMMMM... They put a screw in there to adjust the spring compression and even have a corresponding pass-thru hole in the TBI body for adjustment-screw access, yet they weld the screw.....Were they unable to consider the longevity of that spring and the possibility that a replacement might need adjustment? The solder plug behind the throttle-stop screw in another head-scratcher......They believed that the electronics could manage all these functions without mechanical intervention and they are mostly right! (mostly)

The TBI units were factory adjusted to what they felt was the correct operating pressure for what they were after. After the TBI left the calibration stand it was then sent down the line to be permanently fixed to prevent "tampering". Apparently they had calculated that at a certain pressure and pulse width the fuel injector would deliver the correctly calibrated amount of fuel for the given situation, known as a fuel cell. Basically a look-up table for any given condition and then was adjusted via block learn and integrator, at the time, better known today as short term and long term fuel trim and given as a percentage of adjustment. This was also to make up for variables encountered during everyday engine operation, i.e. vacuum leaks, low fuel volume, low fuel pressure, etc...

Yeah, from day one, emissions equipment had to be manufactured as tamper proof as possible, since the government made the manufacturers liable for any emissions fixes required within 50k or 100k miles. I forget which number; It's been a loooong time.

Today's vehicles have an 8yr/80,000 miles emissions warranty that most people do not know about. I cannot remember when GM started this practice, but if I had to venture a guess I would have to say when OBD II rolled out in 1996. I believe this became the standard no matter the manufacturer. Up until that point it was just the basic 3yr/36,000 miles warranty, but each manufacturer had their own idea of what coverage should be back then.

The lesson I learned here:
I should have looked at where the adjustable plunger tab was adjusted and right away realized that I needed more compression

Welll...
I've now run some gas through since increasing the regulator pressure... The car went from getting 13mpg in town to now getting less than ten!.... I'm gonna hafta revisit the issue...