Follow up on '94 STS surging, stalling, etc.

[Monaco500]

Hey guys,

Here’s the update on troubleshooting my ’94 STS:

Thanks bodybyfisher for your lead. I wrote gmotors.com for a quote. I described the situation and asked if they new if their computer with that service number had the MAP circuit updated; he wrote back and simply said that I need a dealer to run diagnostics to find out for sure.

Yesterday, for grins, I took the top plate off of the intake to check the fuel pressure regulator. (I thought that it may be leaking since my mileage has decreased so much). While the FPR was not leaking, I noticed that the wire coming from the harness to the “C” terminal of the MAP sensor had about ¾” of exposed wire. The wire had a connector with a wire spliced that went to the intake air temperature sensor. There was a lot of oil residue at the base of the wiring harness where it came into the intake; I cleaned it up, and taped the exposed wiring. I put the top back on the intake, torqued it down per the sequence posted by Vince (thank you!) and started the car. As I expected, it ran fine. I let it idle until it reached 208 degrees, then shut it off, and immediately tried to start it. Wouldn’t start for the first few tries, then started hard with erratic idle. I shut it off. Tried to start it again. Same thing. I went into diagnostics… No Codes!

I didn’t drive it (just let it idle), but am thinking that my stalling problem is not MAP/PCM related; I think the PO32 and PO71 codes were from the exposed wiring coming out of the harness.

One thing I noticed, after I bought the car, when I shut it off, I could hear a quiet motor-like noise: Three pulses, then a longer sound. It would do this two or three times and then stop. If I had my foot on the gas pedal, with each of the first three “pulses”, the gas pedal would slightly come up. The pedal would drop down to its original location with the longer sound at the end. Was this the PCM calibrating the ISC module? Did it have something to do with the fuel system? The car does not make those sounds now when shutting it off. Is this related to my problem?

I’m getting discouraged trying to fix this car; I am moving out of the country in two months, and can’t sell it until I fix it…

Thanks for your help.

[adallak]

First, do not get discouraged. You will figure out. Yes ISC motor adjusts after you shut down the engine. Nevertheless, if the sound it makes is unusually loud, it might be bad and needed to be replaced. Unfortunately, I cannot comment on the rest.

[PAUL T]

Do the Idle Learn procedure now. That could be what is causing the erratic idle until the computer gets used to the new signals from the MAP sensor. Drive it a little after then report back.

[Monaco500]

Hello everyone, new update. Before redoing the idle learn procedure, I figured I would record the TPS min and max values to see if the ISC was properly adjusted. When I first checked, the max and min values were the same, at 84. I turned the plunger out, and again, both values were the same at 92. No matter how I adjusted the plunger, both min and max TPS values were identical, so I could never get a difference between 10 and 11 degrees. I need to do the PCM output cycling PO007 to see if the plunger retracts/extends. Any other thoughts?

After starting the car, shutting it down, of course I still had stalling, hesitation, and hard starting when re-starting it. After a few rounds, the temp was going up (around 220 F), and once I got it started again, the idle was fluctuating between 1000 rpm and 1500 rpm, but the plunger for the ISC wasn’t cycling in and out, so that wasn’t the cause. What would cause a fluctuation in RPM of that magnitude without the throttle being pushed in and out by the ISC?

One other significant note, I thought I should check the oil, as I should be about a quart low by now. The oil level was at max, and appeared thin. I smelled it and it smelled a bit like gas. Could this be from sticking/leaking fuel injectors? Would the variable rpm be from injectors cutting in and out? Could it be a cracked fuel rail (I’ve been reading about these on the ’95 northstars)? Would I get a code if I had leaking fuel injectors?

Sorry if my questions seem stupid; I am used to working 50’s – 60’s Mopar, and am just not used to this ”high tech” repair!

Thanks for all of your help,

Eric

[Ranger]

I don't think you would get a code from a leaky injector. Gas in the oil would certainly be from an injector leaking after shut down. The gas would then leak past the rings into the oil pan. A leaky fuel rail would leak into the manifold on a '94 and be burned.

[tommyjack]

For what it is worth, do a search on my user name and see what a problem I had trouble shooting my 92 STS with idle problems. Its fun at first, then gets personnel. My final option was to take it to the stealership and put it on the computer. Costs 63.00. Well woth it. Good luick.

[Monaco500]

I want to tackle my car one problem at a time, but if I have a leaking injector, is it difficult to determine which one? How hard are they to replace? Are they expensive?

Would a PCM problem cause the injectors to discharge fuel after shutdown?

On another note, I have gotten alot of response that I need to go with a GM PCM. The price was much better at Rock Auto, but after already replacing it once, I am nervous about having mine repaired or buying one that is not GM. gmotors.com wanted $165 plus core charge and shipping. Someone told me that I could also have a bad PROM chip. Would that cause my problems?

Thanks guys,

Eric

I don't think you would get a code from a leaky injector. Gas in the oil would certainly be from an injector leaking after shut down. The gas would then leak past the rings into the oil pan. A leaky fuel rail would leak into the manifold on a '94 and be burned.

[Ranger]

Here is some info on checking for leaky injectors.

http://www.cadillacforums.com/forums/cadil...l-injector.html

I seem to recall them being about $80 apiece but could not swear to that. Once the rail is pulled, they should be pretty easy to remove. I do not believe that the PCM would cause an injector to leak after shut down.

[PAUL T]

A quick check for a leaky injector would be to pull the injectors out and have someone turn the key on (engine off) to pressurize the system and see if any injector is leaking. They just pop out, but be careful of the rubber seals.

[Monaco500]

Hey guys,

Here's the latest...

The car died again, but got a new code: PO19 (fuel pump circuit). I gave up and towed it to the dealer. They said that I may be having PCM problems too, but that I likely need a new fuel pump because they are getting inconsistent (and low) pressures from the pump. Apparently the car will no longer stay running; they pushed it in and out of the shop. They said that a pump (discounted) costs $397.41. I need to check gmotors.com and rock auto.

Any thoughts? I know the pump is in the tank. Is this something I can do, or should I just give up and have them do it? Is it possible that this could be the third shop (not counting my efforts) that has diagnosed my car but not solved the problem?

I just took a job in Australia, and need to sell the car in two months before I leave. It pains me to keep sinking so much $$ into the car knowing that it is just worth $4500 at best.

Anyway, thoughts would be appreciated.

Thanks!

Eric

[BodybyFisher]

You will need to drop the gas tank after either running it low or syphoning out as much as possible. Some have done that job here but I don't think its a picnic, but its not hard, the more gas your get out the better. That price for the pump is about right for the dealer but you can do better at Rockauto for $241.. Good Luck down under..

[Monaco500]

Thanks for the good luck wish.

One quick question, I had my fuel filter replaced last year. I have read posts that say that just one bad tank of gas can clog a filter. If my filter (or inlet sock on the pump) were clogged, would I get the PO19 code? I am a little confused because my problem was intermittent for so long; to me it sounds electrical. Could it be the wiring harness? Do the pumps slowly fail like that until they cannot produce enough pressure to keep the car running? Why would the car run well for a while, and then surge/stall only when shut down and restarted again?

Thanks again for your help...

Eric

You will need to drop the gas tank after either running it low or syphoning out as much as possible. Some have done that job here but I don't think its a picnic, but its not hard, the more gas your get out the better. That price for the pump is about right for the dealer but you can do better at Rockauto for $241.. Good Luck down under..

[PAUL T]

Usually the wiring insulation will be eaten away by gas additives and short out on the pump. It can happen over a period of time and finally give out.

[Ranger]

Yes, it is true that one tank of really bad gas could clog the filter but that does not sound like your case. It would not be intermittent.

As far as fuel pumps go, I have seen them go from dying a slow drawn out death to dying in their sleep.

[Monaco500]

Thanks Ranger. Is it possible that PCM could be causing the fuel pressure issues, or is it the other way around: that my fuel pump issues are causing the MAP codes, surging, etc. GMotors.com said that there should be a three letter code off of the fuel pump harness to verify the part number for my fuel pump They want $278. The dealer said the part number is 88962475. Does Rock Auto have a page where I can cross part numbers to be sure I get the right one (if that is indeed what I need?)

Thanks guys,

Eric

Yes, it is true that one tank of really bad gas could clog the filter but that does not sound like your case. It would not be intermittent.

As far as fuel pumps go, I have seen them go from dying a slow drawn out death to dying in their sleep.

[Ranger]

Thanks Ranger. Is it possible that PCM could be causing the fuel pressure issues, or is it the other way around: that my fuel pump issues are causing the MAP codes, surging, etc. GMotors.com said that there should be a three letter code off of the fuel pump harness to verify the part number for my fuel pump They want $278. The dealer said the part number is 88962475. Does Rock Auto have a page where I can cross part numbers to be sure I get the right one (if that is indeed what I need?)

Thanks guys,

Eric

Yes, it is true that one tank of really bad gas could clog the filter but that does not sound like your case. It would not be intermittent.

As far as fuel pumps go, I have seen them go from dying a slow drawn out death to dying in their sleep.

I do not think the PCM can cause low fuel pressure. Not sure about Rockauto but you should be able to cross reference the number at

http://www.acdelco.com/