Rumblin70SS

Hello all,

First, I did a search and while I found a bunch of info, I can't say that I have everything I need to fix this issue. When I start my car, it will immediately die if I don't keep my foot on the gas and nurse it until the car warms up. Once it does warm up, it seems to idle rougher than it should. It also seems to be a little down on power compared to previous cars and it has a light stumble right off idle. The car is completely stock.

So far, I've done a complete tune up including plugs, wires, cap rotor, distributor and set the timing at 10 degrees. I checked the fuel pressure, which while running is about 35 psi and 45 psi with the vacuum line off the regulator. I tested the regulator with a vacuum pump and it holds stready with no loss in pressure. One thing I did notice was that once the fuel pump primes, it immediately drops to zero. It does the same thing once I shut the car off. This happens in a matter of seconds. I'm leaning towards the fuel pump or injectors but both were replaced previous to me buying the car. How else can I test these items? While I don't mind spending money, I sure don't want to just throw it away.

Thannks in advance for the help!

paulo57509

Since the problem seems to be coolant temperature related, I would look at the coolant temp sensor first off.

If you have a service manual, it should have resistance specs for various temps. Barring that, you can always take a reading with a DVM at the sensor when the engine is cold and another when the engine is hot. You want to at least see some kind of response from the sensor at different temps.

If you have access to a scan tool, you can read the coolant temp directily.

Rumblin70SS

Thanks for your reply, I appreciate it. I am working on borrowing a scanner so I can read the coolant temp sensor. I do have the factory service manual and I saw where you can read the resistance of the sensor with a DVM. Only thing is, I don't know how I can get a DVM down where the sensor is at, hence getting the scanner.

I also adjusted the TPS sensor, which wasn't out much, but it seemed to make a difference. It was set at .043 and I moved it to .054. It still starts and stalls one time, but after that I don't need to nurse it. Also the stumble is gone which is another improvement.

While all of this helps, it still doesn't address the fuel pressure dropping. Any idea on testing that?

defaced

iTrader: (6)

MAF Sensor? Just a thought, unless yours is SD.

Rumblin70SS

She is MAF......but the sensor is pretty new according to the last owners receipts and I have no codes.

defaced

iTrader: (6)

That doesn't really mean anything. I bought a new MAF sensor for mine and in three 3 days it went to hell again and I never had any codes.

It's worth a shot I think. Yeah, a reman one will cost you about $150 but it's easy to install and if it doesn't fix the problem you can return it.

The only reason I'm thinking it's the MAF is because my car was acting the same way when it'd warm up. It'd be fine as soon as you started it and then once you took it out on the road, it wouldn't idle and when you gave it throttle it would bog down, hesitate, and miss fire.

Russ-So Cal

You may have a leaking injector, I'm not sure what else would cause the fuel pressure to drop immediately. You can pull the injectors and have them tested or test them yourself. You will need an empty coffee can or other device to submerge a fuel pump into, a stock fuel pump, a battery with jumper leads, and a set of fuel rails from a v6 out of the junk yard. Install the injectors in the rails, submerge the pump in fuel, and turn the pump on with the battery and jumpers to see if any of the injectors leak. After you test the first 6 injectors, replace two of them with the two you haven't tested yet, and retest.

JulieGTA

Do a search for how to test the voltage/resistance of the injectors, it is very common for them to go bad. I think it just takes equipment for testing wires and a noid light.
What kind / color are they?

Aslo to tell if an cylinder is not firing, (if it has headers,) then that tube is alot colder.

Also if you pull one of the spark plugs it could be wet with fuel, or blacker, or whiter than the other plugs which indicates rich or lean.

boldguy

The car likes 10* BTDC?? Mines a 92 tpi and i thought all/most SBC's like 6*.

burnout88

If your pressure drops to zero after shutting off the car you found the problem. Your injectors are leaking. They can even show good on the ohm test but the nozzles will leak. Very common problem. Get a new set of ford injectors and be done with it.

Rumblin70SS

I'm thinking it might be the MAF too, but I didn't want to buy it and the MAF not be the fix. I didn't think you can return electrical parts, so I'll have to find out if they will let me do that. Just as some info, when the car starts, it still stalls a few times unless I nurse it. When I disconnect the MAF, it starts, runs and drives better for the most part. It does have an occasional problem with idle though like when stopped at a light. GM's manual says that if you disconnect the MAF and it runs better and there are no connection issues the MAF might be the problem. I want to play with the IAC valve and the EGR, and if that doesn't have any affect, I'll replace the MAF.

I went through the GM service manual and the fuel pressure test with crimping off the rubber lines is pretty easy. I made it all the way to where I eliminated everything except the regulator. When I did that test, the pressure went way up (80 psi) and when I released the hose, it dropped back to about 45 as it should. Ever since then, its been holding correctly. It does drop by about 10 lbs over the course of about a half hour and is zero by the next morning. Its almost like the regulator was stuck and thats possible because the car really hasn't been driven much in the last 3 years. Now it catches right away when you crank it, which is a definite improvement. Is there a rate the fuel pressure should bleed off or should it stay at 45 PSI until you start the car again. I can't imagine that the fuel system would retain that pressure overnight which is why GM does the 2 second key up with the fuel pressure when the key turned on.

I checked out the injectors and they look to be a metal/silver body with a tan top. I think by the appearance of them they are Bosch II's. I would assume they were factory replacement injectors and were installed about 3 years/5000 miles ago according to the receipts. Either way, I will do the search and test out the injectors. They are easy to get to so testing shouldn't be an issue.

The car still has stock manifolds and when I replaced the plugs during the tune up, they all had the normal tan appearance. The car had the same issues when I was doing tune up also.

In the past, I have always ran my cars with 10* timing. The most recent one was a 92 which was a SD car I sold in June. I do run premium gas always, so that might make a difference. If all else fails, I'll drop the timing. I'm not sure 4* would make that much of a difference, but anything is possible and its free to try!

Thanks for the input, although I think I have minimized the injector problem for now. Is the ohm test what JulieGTA was referring to?

Thanks again all for the input!

defaced

iTrader: (6)

Sweet man, sounds like you're figuring out your problems. I'd still put money on the MAF though. Especially after you said when you disconnected the MAF, the car ran fine. That's a huge sign right there that your problem is originating at the MAF. Good luck! Let us know how it goes.

Rumblin70SS

We are slowly getting there as I've fixed a ton of crazy problems already. The manual helps, but everyone piping in to help is one of the best parts of this site. There is no subsitute for personal experience.

I searched for the injector ohm test and found a video on it. I tested all the injectors at an ambient temperature of 42 degrees and all came out to either .016 or .017 so we are good there.

Another test I performed was leakdown in the fuel system. I turned the key on a observed a fuel pressure of 40 PSI. In exactly half an hour, the pressure was out 24 PSI and in an hour it was 14 PSI. Is this normal, or what I would consider leaking? I can't imagine the fuel system holding pressure for days or weeks. If it isn't normal, I know this can be caused by injectors, but would a cold start valve cause this also? How about the regulator? If so, I'll replace that first as I had an issue with that in the beginning. I think these problems might cause some difficulty starting, but aren't the root of my issue.

southbay08

pull the spark plugs, if any of the cylinders are wet, you have one or more leaky injectors.

Rumblin70SS

If the plugs weren't so much of a pain to pull, I would. Last time I did a tuneup, which was only a few months ago, I didn't see any wet plugs. I'll have to go after it again once I figure out the driveability issue.

Rumblin70SS

Just a heads up, I ordered the MAF sensor and should have it tomorrow, but probably won't get it on until sometime Wednesday. I'll let you know if it makes any difference.

Rumblin70SS

Ok guys, I finally got the MAF and installed it on the car. I purchased a new one from Advanced Auto which has the circuit board in it. It's a little different than what I am used to, but after reading about it on TGO and added to the fact that it has a lifetime warranty I decided to give it a shot.

With the cold start, it worked perfectly. The car started right up, but the SES light didn't go off from when I had the old sensor disconnected. I cycled the battery and the light didn't come back on. I let the car warm up and it seemed fine. I took it for about a 5 mile ride and while it seemed to respond better, it still idles a litte rough and also lacks power as before. I'm gonna drive the car for a few days and see if it impoves and if not, I'll be looking for some other avenues to test. At the very least, I don't have a SES light on and I can start the car without worrying about it stalling out for the first 10 minutes.

uppercuts

You might have to replace the IACV also or relearn it to the new MAF sensor.

Rumblin70SS

Actually, the rough idle issues were the injectors which I replaced with FIC Bosch III's. Fixed all the idle problems!