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'94 STS Engine stalling problems


Monaco500

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'94 STS Engine stalling problems

Hello everyone,

I have been having very frustrating problems with my 94 STS. It will run fine when starting up cold. I then drive it for 15 minutes or so (fully warmed up - temp around 210), park it to run errands or what ever, get back to the car, and then have problems. Sometimes it will run fine for a minute or two, then the idle becomes extremely erradic, the car sort of chokes and gags, then dies. I then restart the car, and it chokes a little more, then dies when put under load. Other times, it will choke immediately and die.

I have checked codes and since replaced the MAP sensor, TP sensor, IAC module. Same problem with PO26, PO32, PO52, PO53, PO71, PO95, PO109, IO52, SO36, and SO44 codes. I had the car towed to a shop, had diagnostics performed. They said I needed a new PCM.

I ordered one, installed it last night, and the car started fine, but listed TO72, SO36, SO44, PO52, PO80 (current), P109, and IO52 with the check engine light on. After driving it for 15 minutes w/o problems, I let it sit for 20 minutes, started it, and drove it less than 1 block when it started choking and stalling again. I limped it back home, and am now back to the drawing board. I haven't ran the codes after the last stall yet; it was getting late. Getting frustrated spending all this money without fixing the problem.

Any ideas what this may be? The shop said that they checked all of the sensors I replaced, and they tested fine, leading them to believe that the PCM was the problem.

Please help; I'm spending way too much money fixing this car and cannot keep borrowing my loaner car for too much longer.

Thanks in advance!

Eric

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P080 is a code for FUEL SYSTEM RICH, immediately check your FPR (Fuel Pressure Regulator).

P052 is no big deal its the PCM Memory Reset (disconnecting the battery will do that)

P109 Keep Alive Memory (KAM) Reset/PCM has lost primary battery power (no problem battery disconnect)

Check the FPR. I am not sure where it is on a 94, I think its under the intake maybe, but if you can get to it, pull the vacuum hose, if there is fuel, replace it. I don't know the 94 well to help you further.

Mike

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

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On the '93/'94, the FPR is inside the intake manifold, hence no vacuum line to it. Remove the top of the manifold, turn the key on but DO NOT start the engine. Look for fuel leaking from the nipple on top of the FPR. If there is any, R & R the FPR. The FPR is mounted on the fuel rail.

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Every time I see a long list of error codes I suspect bad grounds and other electrical contacts. Check out and clean the battery cable contacts and grounds. A jumper from the battery's negative terminal to a reliable engine point would not hurt either.

Besides, as BBF and Ranger suggetsed, turn the ignition ON (engine is OFF) and pull the vacuum hose from the FPR. There should not be any fuel dropping from the FPR. Here is a FPR on my car. Yours may look similar.

BTW, the new PCM could be bad too.

post-312-1140048382_thumb.jpg

The saddest thing in life is wasted talent

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If the FPR is faulty, would that explain why the car would run fine for the first drive (15 min or so), then when starting to take off again the car bogs down and surges? Could the surging and stalling be setting the codes?

Now that you mention it, my mileage has been decreasing from 21 to 18 over the past few months...

Every time I see a long list of error codes I suspect bad grounds and other electrical contacts. Check out and clean the battery cable contacts and grounds. A jumper from the battery's negative terminal to a reliable engine point would not hurt either.

Besides, as BBF and Ranger suggetsed, turn the ignition ON (engine is OFF) and pull the vacuum hose from the FPR. There should not be any fuel dropping from the FPR. Here is a FPR on my car. Yours may look similar.

BTW, the new PCM could be bad too.

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The FPR has a rubber diaphram in it that could be sealing intermittantly thereby causing your intermittant problem, I would look to it at this time. Its only about $40 to $50

Also, we just recently had a member that had a NEW PCM that was also bad, as Adallak stated. When I read your list of problems I was thinking PCM until I saw it was replaced. Ranger nicely described the method to diagnose it.

I hear your frustration about spending WAY too much money but realize you are driving a complex 1994 car that will have higher than average repairs. If those repairs get to a point, say $400 a month on average, its time to buy a NEW car...and have a new car payment.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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You probably saw the PCM installed. It is under glove box. You or a helper might want to tap-test it when the car acts up to see if it makes difference. A bad PCM can drive one crazy, that's for sure.

The saddest thing in life is wasted talent

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After doing some more reading on this great site, I see that I should clean my fuel rails and phenolic plates. Is there a thread outlining this procedure and anything I should watch out for?

I hear you have a thread for diagnosing the PCM; do you have a link to it?

Thanks Ranger!

Eric

On the '93/'94, the FPR is inside the intake manifold, hence no vacuum line to it. Remove the top of the manifold, turn the key on but DO NOT start the engine. Look for fuel leaking from the nipple on top of the FPR. If there is any, R & R the FPR. The FPR is mounted on the fuel rail.

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You can clean the phenolic spacer plate but fuel rails do not get cleaned. The Phenolic Spacer would not cause an intermittant problem. I still think you need to look the FPR over. There is no real thread for diagnosing the PCM, the PCM is usually the last resort when all else fails, tapping on a PCM can sometimes elicit a symptom.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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P080 is a code for FUEL SYSTEM RICH, immediately check your FPR (Fuel Pressure Regulator).

Mike,

P080 is TP Sensor/Idle Learn Not Complete on the Northstar. What you quoted is for the 4.9. If the code does not go away after Idle Learn is done it may be one of the following sensors bad: Throttle Position Switch, TP sensor, Vehicle Speed Sensor, Transaxle Range Switch, Power Steering Pressure Switch, or Brake Switch.

With all the codes showing I say it is electrical or the PCM. Are all the fuses O.K.? What about condition of battery terminals, are the connected good and not corroded? Have they been cleaned? What about grounds? Is the PCM plug properly seated?

What about Fuel Pump or Relay?

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Good pickup Paul, I went to caddyinfo how to and picked up OBDI 93 to 95 in error, thanks... my mistake

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Good pickup Paul, I went to caddyinfo how to and picked up OBDI 93 to 95 in error, thanks... my mistake

I almost did not catch it myself. I was looking at my 94 manual and did not realize some of the codes for the 4.9 and 4.6 were different until today. I even have 2 sections for the other codes that differ between the Concours and the Eldorado/Seville. Maybe that is why the 94 manual is 2 volumes. The learning never stops.

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His symptoms contributed to me believing that the code I picked up was right... :lol: I looked back and sure enough he didnt mention FPR... LOL.. I have been decreasing the time I spend here, I can see, I need to read and think carefully going forward, lessons learned...

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Hey guys,

Thanks for the input. The ironic thing is my symptoms are the same now as they were before I replaced the PCM, however, I didn't get the PO80 code with the original PCM. That code has been up only with the new PCM.

The car runs fine for the first 15 minutes or so, then it acts up, especially if it has been sitting for 20 minutes or more after driving for 15 minutes. Would battery connections/grounds or the fuel pump/relay only fail after the car sits for a while after a 15 minute drive? When I had the car in the shop, they said they had the car running all morning without problems. It was only later that afternoon that they got the car to act up.

I checked the codes last night after it failed with the new PCM. For comparison:

Codes after symptoms before replacing PCM (after replacement of TP sensor, MAP, IAC module):

PO26, PO32 (current), PO52, PO53, PO71, PO95, PO109, IO52, SO36, SO44

Codes after symptoms with replacement PCM:

PO32, PO52, PO71, PO80 (current), PO95, PO109, IO52, TO72, SO36, SO44

I put the original chip in the new PCM when I replaced it as the manual suggests.

Any thoughts?

Thanks again for all of your help...

Eric

P080 is a code for FUEL SYSTEM RICH, immediately check your FPR (Fuel Pressure Regulator).

Mike,

P080 is TP Sensor/Idle Learn Not Complete on the Northstar. What you quoted is for the 4.9. If the code does not go away after Idle Learn is done it may be one of the following sensors bad: Throttle Position Switch, TP sensor, Vehicle Speed Sensor, Transaxle Range Switch, Power Steering Pressure Switch, or Brake Switch.

With all the codes showing I say it is electrical or the PCM. Are all the fuses O.K.? What about condition of battery terminals, are the connected good and not corroded? Have they been cleaned? What about grounds? Is the PCM plug properly seated?

What about Fuel Pump or Relay?

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Check for a bad CAT or an exhaust restriction.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Bad electrical contact/contacts may depend on the temperature. Have you heard of "no start when engine is hot" condition? It is completely electrical problem inside of the starter. Car starts perfectly when engine is cold, but you shut it down when it is hot and cannot restart for 30 minutes or so.

Why won't you just check the battery cables for internal corrosion and put a jumper to the engine to ensure you have at least one good ground? These are easy to do tests and they cost nothing ot next to nothing.

The saddest thing in life is wasted talent

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S044 - Lift/Dive signal fault - My Manual says that it could be caused by the PROM Chip not properly seated in PCM. You might check that.

My 92 Deville did what you are describing and it turned out to be a loose connection at the battery terminal. I thought it was the PCM. It would run fine, then start acting up, then die, mostly coming to a stop. Most of the time it would start back up and be o.k. for about a week then, out of the blue, it would miss and carryon aweful again. I went to start it one time and I guess the terminals got so loose that it would not turn over. I cleaned and tightened the terminals and it has not acted up since.

I would check the battery terminals. Clear your codes, drive it until it act up again then recheck your codes and report back. The P080 would be naturally set due to the new PCM if you did not do the Idle Learn procedure. P052, P0109, & I052 all have to do with the battery being disconnected. P032 & P071 have to do with the MAP sensor. There could be a short or ground problem causing them, this could also be the problem for the S036 & S044. P095 is of course from the engine stall. I am not clear what T072 is but if it has to do with traction control, it could also be a ground or short problem.

Was the PCM a rebuilt aftermarket or bought at a GM dealer?

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Hey guys,

Those are good suggestions; I'll check the battery cables and add a jumper cable to the engine.

The PCM was a rebuild from www.autoecms.com. The rebuild actually looked rougher than I would expect; when I removed the cover to put in my PROM chip, the board inside appeared dirty; not clean and free of debris like my original PCM.

I think I'll check the fuel pressure regulator regardless, since the car has 145k.

Thanks for your help... I'll let the board know how it goes...

Eric

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On the '93/'94, the FPR is inside the intake manifold, hence no vacuum line to it. Remove the top of the manifold, turn the key on but DO NOT start the engine. Look for fuel leaking from the nipple on top of the FPR. If there is any, R & R the FPR. The FPR is mounted on the fuel rail.

I would not bother with the FPR until you check the battery terminals. If you check the FPR just remove the 12 bolts only on the cover. The 4 bolts in the middle hold the manifold in and do not need removed. Follow Rangers instructions, and if it is bad, fuel will spew like a whale from the nipple on top when the system is pressurized. DO NOT START THE ENGINE WITH THE COVER OFF.

I would be leary of your PCM if your battery terminals are O.k.. Aftermarket parts do not work well with a Northstar, only get GM parts and save yourself a lot of hassle.

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Hey guys,

Haven't checked the battery cables yet; plan on doing it this weekend, but have two other questions:

I found a thread for the Idle Learn Procedure for the 4.9L motors; is this the same for the '94 STS? If not, is there a thread I should refer to? Could part of my problem be that I did not set the screw correctly on the IAC module when I put it in?

Also, when I was troubleshooting my problems last week, I was told that it could be the EGR valve. I checked into availability from local parts stores and found that no stores listed a valve for the '94. THe '95 looked identical, but none of the store computers said it was compatible with the '94. Is there a thread for the cleaning procedure of the EGR valve?

Thanks guys, I'll report back on Saturday to see how sucessful I was...

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If you buy an EGR valve only buy an OEM unit they are calibrated for your engine.

You can take the EGR off and clean it with wire brushes, small and large, the key is to clean the pindle seat, i use 22 caliber rifle cleaning brushes. You can use solvent to soak it also but be careful not to get the solvent into the diaphram or coil works. Here is my EGR after cleaning, before cleaning it was sticking after cleaning it was nice and smooth, use a torx to turn and hold the pindle

post-2998-1140145289.jpg

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Hey guys,

Haven't checked the battery cables yet; plan on doing it this weekend, but have two other questions:

I found a thread for the Idle Learn Procedure for the 4.9L motors; is this the same for the '94 STS? If not, is there a thread I should refer to? Could part of my problem be that I did not set the screw correctly on the IAC module when I put it in?

Also, when I was troubleshooting my problems last week, I was told that it could be the EGR valve. I checked into availability from local parts stores and found that no stores listed a valve for the '94. THe '95 looked identical, but none of the store computers said it was compatible with the '94. Is there a thread for the cleaning procedure of the EGR valve?

Thanks guys, I'll report back on Saturday to see how sucessful I was...

Good places to look for OEM parts are www.rockauto.com and www.gmpartsdirect.com

Paul seems to find your problem - a bad PCM or/and PROM, or the related contacts. I would not waste my time replacing EGR, ISC etc. before PCM and battery cables, grounds are checked and cleaned. You can address any minor issue later when you get rid of most of trouble codes.

The saddest thing in life is wasted talent

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  • 2 weeks later...

Hello everyone,

Here's the update:

After a weekend of well below zero temperatures, we are now having near record highs along the Colorado front range. That means it's been warm enough to do the idle learn procedure with the A/C compressor kicking in.

On Sunday, I replaced the negative battery cable, cleaned posts on both terminals, and ran a negative jumper. I put the original computer back in, cleared codes, and test drove it.

When I first jumped on it, it coughed, so I let off the gas. THe idle returned to normal, and it drove fine for the rest of the afternoon under different driving conditions. Good to have the Caddy back.

That evening, it coughed on me a few more times. I had a PO71 (intermittent MAP sensor) code. I cleared codes, went through the idle learn procedure again, and drove it around the block a few times. No problem, but the idle was much higher, around 1000 rpm. It would also be pushing between 1000 rpm and 1500 rpm when coming to a stop. I replaced the ISC module about a month ago.

Yesterday, when driving it to work, the idle was a little high, but not as bad as the night before. Driving it home from work yesterday, the idle was back to normal, and the car drove fine.

This morning however, I had a few problems. After driving it 20 miles to the post office (ironically to mail back the replacement PCM I had bought a few weeks earlier), it had the same symptoms as before: After driving the car for a while, sitting for 15 min, and driving again, the idle would cut out, and finally stall. I limped the car to my office a few blocks away (The idle was cutting out, but if I let off the gas the car wouldn't die). I ran codes and got PO71 (intermittent MAP) and PO95 (stall).

Any thoughts, or should I just hope for an encounter with a Cement Truck? :)

Thanks guys,

Eric

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Hello everyone,

Here's the update:

After a weekend of well below zero temperatures, we are now having near record highs along the Colorado front range. That means it's been warm enough to do the idle learn procedure with the A/C compressor kicking in.

On Sunday, I replaced the negative battery cable, cleaned posts on both terminals, and ran a negative jumper. I put the original computer back in, cleared codes, and test drove it.

When I first jumped on it, it coughed, so I let off the gas. THe idle returned to normal, and it drove fine for the rest of the afternoon under different driving conditions. Good to have the Caddy back.

That evening, it coughed on me a few more times. I had a PO71 (intermittent MAP sensor) code. I cleared codes, went through the idle learn procedure again, and drove it around the block a few times. No problem, but the idle was much higher, around 1000 rpm. It would also be pushing between 1000 rpm and 1500 rpm when coming to a stop. I replaced the ISC module about a month ago.

Yesterday, when driving it to work, the idle was a little high, but not as bad as the night before. Driving it home from work yesterday, the idle was back to normal, and the car drove fine.

This morning however, I had a few problems. After driving it 20 miles to the post office (ironically to mail back the replacement PCM I had bought a few weeks earlier), it had the same symptoms as before: After driving the car for a while, sitting for 15 min, and driving again, the idle would cut out, and finally stall. I limped the car to my office a few blocks away (The idle was cutting out, but if I let off the gas the car wouldn't die). I ran codes and got PO71 (intermittent MAP) and PO95 (stall).

Any thoughts, or should I just hope for an encounter with a Cement Truck? :)

Thanks guys,

Eric

Eric,

You can disable ISC motor by turning ignition on, holding up throttle lever and pressing the ISC motor's plunger till it retracts completely . Disconnect the ISC motor at this point (you will see connector). You will need to press the gas pedal a bit when you start the car to prevent stalling, but at least car will be driveable otherwise.

Well... let's think what could cause all this.

The saddest thing in life is wasted talent

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You keep getting P071, I would look at that first for a bad MAP, short or bad connection.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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