: 94 STS starts only if pressing gas, idles rough, dies after a couple minutes



whoaskew
12-22-07, 09:22 PM
I searched the archives and it told me to do the exhaust gas test on my 98 deville and it told me my headgasket is bad.

As a result, I need to get the 94 STS running properly that I bought in October for $1200. It only has 60,000 miles on it.

Problems it had when I bought it:
1. Transmission always stayed in 2nd gear
2. Horrible fuel mileage - around 10mpg
3. The dash displayed ---- for some sensors (coolant temp and mpg) but others work (battery voltage, rpm)
4. Engine rotated, but wouldn't start unless I was pressing the gas pedal
5. Engine would die while driving if I didn't keep one foot on the gas at all times

Things initially replaced:
1. fuel filter, 2. air filter, 3. transmission shift solenoids

None of the problems were fixed. Transmission still stayed in 2nd gear, so the mechanics replaced it with a $350 one from a junkyard that came with a 90 day warranty. This transmission was supposedly pulled from a wrecked 97 deville. Everything bolted up except the neutral safety switch, so we used the one from the old transmission.

While at it, they also replaced the following:
Battery, water pump mouting gaskets (NAPA part #s 35658 and 35656), added the bars leaks tabs, changed the serpentine belt, water pump belt, hoses, spark plugs, STP throttle body cleaner (throttle body was suprisingly clean), and 3 transmission seals (both axle seals and I believe the 3rd was the rear main seal).

After the transmission was installed, they were filling it with fluid and noticed a 2"-3" horizontal crack in the rear transmission cover (next to the front driver side tire). The mechanics lowered the frame, removed the cover, and saw the transmission filter inside was loose. The seal that held it on was bad, so we replaced it (GM part #8678599). We used the cover from the old transmission.

They put everything back together and tried to start the car. The engine rotated, but would not start. I checked the archives and it said to look at the crankshaft position sensors, they were either broken or disconnected. Sure enough, that is what happened. Apparently, while lowering/raising the cradle to remove the transmission, the two wires to the CPS were snapped, when they got lodged under/around the motor mount near the radiator. We went to the dealer and bought a new pair of pigtails with wires that we spliced into the old wires.

Tried starting the car, rotated but wouldn't start. Pressed the gas pedal a little and it started but ran rough. Thought the CPS wires might have been crossed, so we switched those, but then it wouldn't start at all with or without gas.

Switching the CPS wires back to the correct way led to the following:
Without gas - the engine would only rotate. Lightly pressing the gas, would start but rpms around 500, acted like it was starving for gas. Press the gas all the way, rpms only go to 800, occasionally engine would pop (backfire?) and die after a few minutes.

The mechanics said they think it is the fuel pump even though you hear the fuel pump running for a few seconds when you turn the key to the on position. They had no fuel pressure gauge, but while the car was off, they pushed the fuel valve by the throttle body and fuel only dripped out. They said it should have sprayed him in the face. With the key on (but engine off), it sprayed a little but died down. If I turned the key on and off rapidly, it built up pressure and shot a much stronger stream when the valve was opened.

I called the auto parts stores and they said before replacing the fuel pump to try the fuel pressure regulator or the throttle position sensor.

I replaced the fuel pressure regulator today, and saw no improvement.

Any ideas before I buy a fuel pump?

whoaskew
12-22-07, 09:26 PM
Pulled the codes on the dash and got the following;

P015 - Open Coolant Temp Sensor Signal
P052 - PCM Memory Reset
P053 - Distributor Signal Interrupt
P080 - Fuel System Rich
P109 - Keep Alive Memory Reset/ PCM has lost primary battery power

I032 - Loss of ABS Data
I033 - Loss of Supplemental Inflatable Restraint Data
I034 - Loss of Powertrain Control Module Data
I037 - Loss of Air Conditioning Programmer Data
I039 - Loss of Road Sensing Suspension Data
I041 - Battery Voltage too low
I052 - Keep Alive Memory Error

A011 - High Side Temperature Sensor Circuit
A037 - Loss of Instrument Panel Sensor Data

T072 - Serial Data Link Fault
T073 - PC EBTCM/EBCM Pulse Width Modulation Signal Fault

Ranger
12-22-07, 09:48 PM
Any ideas before I buy a fuel pump?
Buy a fuel pressure gauge.

zonie77
12-22-07, 10:42 PM
Did it run well before you had the trans changed? If so then it's 99% probable that the trans guys did something to cause the problem. Before you change anything else get the fuel pressure gauge and check the pressure.

If it isn't fuel pressure check all the vacuum lines and all the wiring that you can see. Especially around the throttle area.

Clear the codes and see what comes back. A weak battery will throw false codes.

Harbor freight has fuel pressure gauges at a reasonable price. If it's on sale it's usually less than $10.

zonie77
12-22-07, 10:50 PM
When yo9u are checking wiring consider how they lowered the cradle and what they might have damaged if they went too far.

zonie77
12-22-07, 10:50 PM
When you are checking wiring consider how they lowered the cradle and what they might have damaged if they lowered it too far.

Ranger
12-22-07, 10:52 PM
Another thought comes to mind. If it only starts with your foot on the pedal, then the throttle plate is completely closed and the engine will never start as it is completely choked. Watch the ISC motor when the key is turned on. Does it activate and extend to open the throttle plate a bit?

kdcing
12-22-07, 11:46 PM
As mentioned already:

1. Clear codes and see which codes return.
2. Check ISC for extension (although, something else must be wrong if rpm's only go to 800rpm @ wot)

If the above 2 things don't help, and if the P053 code returns after clearing the codes, then check out these 2 references:

http://www.cadillacforums.com/forums/ht4100-4-1-4-5-4/123965-93-eldorado-4-9l-p012-p053.html
(The reference above refers to a bad Ignition module on my 4.9L. It appeared that the bad ignition module shut down the fuel flow, not the spark. If the IM works the same on the Northstar, perhaps your IM has failed in a way that has significantly reduced the fuel flow.)

http://www.v8mr2.com/reference/Tests_with_codes.pdf
(In the above reference, note the P080 error description is different from the description you quoted - fuel rich vs. TPS learn.)

whoaskew
12-23-07, 12:01 AM
Did it run well before you had the trans changed? If so then it's 99% probable that the trans guys did something to cause the problem. Before you change anything else get the fuel pressure gauge and check the pressure.

If it isn't fuel pressure check all the vacuum lines and all the wiring that you can see. Especially around the throttle area.

Clear the codes and see what comes back. A weak battery will throw false codes.

Harbor freight has fuel pressure gauges at a reasonable price. If it's on sale it's usually less than $10.

Other than the fact that I had to keep my foot on the gas, the motor ran pretty well. It would easily rev up to 5000 rpms when on the highway at 50 or 55 mph (remember I was in 2nd gear), and I drove this way for 2 or 3 weeks before I took it to get the tranny changed.

I will definitely get the fuel pressure gauge as well as check out the links you posted.

kdcing
12-23-07, 12:07 AM
After rereading your initial post, there appear to be at least 2 independent problems:



2. Horrible fuel mileage - around 10mpg
3. The dash displayed ---- for some sensors (coolant temp and mpg) but others work (battery voltage, rpm)

P015 - Open Coolant Temp Sensor Signal


Looks like a disconnected or bad coolant temp sensor



4. Engine rotated, but wouldn't start unless I was pressing the gas pedal
5. Engine would die while driving if I didn't keep one foot on the gas at all times
As Ranger mentioned, probably something wrong w/ the ISC.




http://www.v8mr2.com/reference/Tests_with_codes.pdf
(In the above reference, note the P080 error description is different from the description you quoted - fuel rich vs. TPS learn.)
If the TPS learn is the correct error description, then there is something wrong w/ the TPS adjustment or the TPS itself.
If the Fuel Rich is the correct error description, then it appears that the engine is running rich (likely measured by the 02 sensors)....contradicts the theory of a bad fuel pump.

I would start by troubleshooting the coolant sensor, ISC and TPS before investing in a fuel pump that is not proven/tested to be defective.

whoaskew
12-23-07, 12:20 AM
Another thought comes to mind. If it only starts with your foot on the pedal, then the throttle plate is completely closed and the engine will never start as it is completely choked. Watch the ISC motor when the key is turned on. Does it activate and extend to open the throttle plate a bit?

One thing that I noticed while cleaning my throttle body was that I don't have a MAF screen like in these instructions: http://www.cadillacforums.com/forums/cadillac-tech-tips/66742-how-clean-throttle-body.html

Is that how it is supposed to be on this 94 sts?

Is the throttle plate the same as the throttle body blade? (I think so but I want to make sure)

I tried to search for a picture of the ISC motor and location. Can you tell me where to find it?

whoaskew
12-23-07, 12:23 AM
After rereading your initial post, there appear to be at least 2 independent problems:


Looks like a disconnected or bad coolant temp sensor


As Ranger mentioned, probably something wrong w/ the ISC.



If the TPS learn is the correct error description, then there is something wrong w/ the TPS adjustment or the TPS itself.
If the Fuel Rich is the correct error description, then it appears that the engine is running rich (likely measured by the 02 sensors)....contradicts the theory of a bad fuel pump.

I would start by troubleshooting the coolant sensor, ISC and TPS before investing in a fuel pump that is not proven/tested to be defective.

Thank you both. Now I at least know where to start.

kdcing
12-23-07, 12:33 AM
I tried to search for a picture of the ISC motor and location. Can you tell me where to find it?

There is a picture of an ISC on the AutoZone website. It is about the size of a soda can....maybe a bit smaller. On my 4.9L, the ISC is mounted on top of the intake and has a plunger that extends to push the throttle open...on your Northstar, I assume that it is similarly located near the throttle body opening.

http://www.autozone.com/R,APP446893/vehicleId,1954201/initialAction,partProductDetail/store,3555/partType,00210/shopping/partProductDetail.htm

whoaskew
12-23-07, 12:37 AM
http://www.v8mr2.com/reference/Tests_with_codes.pdf
(In the above reference, note the P080 error description is different from the description you quoted - fuel rich vs. TPS learn.)


http://myweb.accessus.net/~090/dtcobd1.html#ide says on cars sold before January 1996 (obd 1) the P080 error code means - Fuel System Rich

http://www.v8mr2.com/reference/Tests_with_codes.pdf says on a 1995 vehicle the P080 error code means - TP Sensor/ Idle Learn Not Complete

Since my vehicle is a 1994, how do I know which to use?

whoaskew
12-23-07, 12:43 AM
There is a picture of an ISC on the AutoZone website. It is about the size of a soda can....maybe a bit smaller. On my 4.9L, the ISC is mounted on top of the intake and has a plunger that extends to push the throttle open...on your Northstar, I assume that it is similarly located near the throttle body opening.

http://www.autozone.com/R,APP446893/vehicleId,1954201/initialAction,partProductDetail/store,3555/partType,00210/shopping/partProductDetail.htm

Thanks, that helps. It has been hard to identify the parts because it has been snowing all day.

kdcing
12-23-07, 12:45 AM
Problems it had when I bought it:
1. Transmission always stayed in 2nd gear

None of the problems were fixed. Transmission still stayed in 2nd gear, so the mechanics replaced it with a $350 one from a junkyard that came with a 90 day warranty.

The mechanics lowered the frame, removed the cover, and saw the transmission filter inside was loose.

I know the transmission has already been replaced, but that loose filter very likely was the root cause for the transmission staying in 2nd gear. Read the post below. I'm not sure if the poster indicates if the issue was w/ the 60E Transmission (i.e. 4.9L) or the 80E transmission (i.e. Northstar), but suspect that it was the same issue on your transmission. You may have a very useable spare transmission (after the filter and bracket are changed). In any case, it is amazing how much information is on this forum and how many of the same problems are experienced by others....good luck in getting the '94 back up (and the '98 going again too!)

http://www.cadillacforums.com/forums/cadillac-seville-cadillac-eldorado-forum/93498-still-stuck-2nd-gear-what-gives.html

whoaskew
12-23-07, 12:55 AM
One more thing. Before I checked the codes, the dash said to change transmission fluid.

I understand that the car gives that message when the fluid overheats, but it was just changed a few days ago and the car hasn't been driven. In fact, it has only ran for a few minutes at a time.

Any ideas why it would give that message?

whoaskew
12-23-07, 01:20 AM
I know the transmission has already been replaced, but that loose filter very likely was the root cause for the transmission staying in 2nd gear. Read the post below. I'm not sure if the poster indicates if the issue was w/ the 60E Transmission (i.e. 4.9L) or the 80E transmission (i.e. Northstar), but suspect that it was the same issue on your transmission. You may have a very useable spare transmission (after the filter and bracket are changed). In any case, it is amazing how much information is on this forum and how many of the same problems are experienced by others....good luck in getting the '94 back up (and the '98 going again too!)

http://www.cadillacforums.com/forums/cadillac-seville-cadillac-eldorado-forum/93498-still-stuck-2nd-gear-what-gives.html

I changed the shift solenoids when I still had the old transmission in the car, which did not make it shift, so I decided to replace it. The new transmission is the one that had the loose filter which cracked its rear transmission cover.

I could have saved the old transmission and used it as a spare, but I went to my mechanics shop a few days ago and I saw one of his assistants taking it apart to recycle the aluminum. I saw the valve body lying on the ground and had him take my shift solenoids off it and put in a bag for me to take home since I had just bought them a few weeks ago. I noticed that on the valve body, the shift solenoids were installed properly with the L-bracket just like in the pictures in the link you posted.

Turns out that since he took the rear cover off the old transmission to use on the new one, the junkyard didn't even want the old tranny back for the core deposit.

I don't know how much the recyclers pay for aluminum, but it sure seemed like a lot of work taking the tranny apart.

I bought this '94 STS as a project car for when I got around to it sometime next summer. At the time, the '98 was running great. It was only a few weeks later that the '98 deville's head gasket went all the way out, so my hand was forced.

Reading other's experiences reminded me that I had been getting some hints from the car that the head gasket was going bad (check coolant level messages, sweet smells on the inside of the car, etc.) while driving but I ignored it because the car ran so well (I put around 60,000 miles on it over the past 2 years). Now I don't have much choice but to get the 94 running.

I miss driving the 98, but right now anything beats walking... :yup:

kdcing
12-23-07, 01:26 AM
http://myweb.accessus.net/~090/dtcobd1.html#ide says on cars sold before January 1996 (obd 1) the P080 error code means - Fuel System Rich

http://www.v8mr2.com/reference/Tests_with_codes.pdf says on a 1995 vehicle the P080 error code means - TP Sensor/ Idle Learn Not Complete

Since my vehicle is a 1994, how do I know which to use?

That is a good question....unfortunately, I do not know the answer. The Mitchell reference indicates that it is for the 1995 Concourse model, but I would guess the information is useable on other Northstar models. Without knowing the answer with certainty, I would attempt tests on both the TPS and Oxygen levels in the exhaust. Of course, I would only do the tests if the P080 code returns after clearing the codes.

TPS: Page 7 of the Mitchell reference shows how to get to the PCM Data. Get to PD01...this will show the angle of the throttle plate. With the PD01 value showing on the dashboard display, slowly press the gas pedal (safer to do w/ engine off). As you slowly press the pedal, the angle number shown on the display should slowly increase to its max value @ wot. If the angle number jumps eradicatically, the TPS is likely bad (I believe the TPS acts like a variable resistor....basically acts like a rotarty volume button on an old type stereo....as the volume dial is turned up, the volume should correspondingly go up). If the tps checks out ok, go to the tps relearn procedure...its around page 200 of the Mitchell reference.

Oxyen Levels: On my 4.9L, the ECON and DEFOG lights on the climate control readout will flicker as the O2 sensors go from lean to rich and visa-versa. It is normal for flicker to occur at the rate of 1 flicker every 1 or 2 seconds to mulitple flickers per second. This flickering only occurs when in the diagnostics mode...specifically, when in the PCM portion of the diagnostics mode. If the engine were to remain in a rich condition, both ECON and DEFOG would stay in the same state (i.e. either illuminated or not-illuminated.....I forget which state means rich). In any case, you may try this test on your car....however, a few cautions

1. The diagnostics on the Northstar may be different (i.e. the ECON and DEFOG lights may be indicators of something other than O2 sensor signals). For example, page 5 of the Mitchall reference state that ECON and DEFOG indicate Transmission solenoid states. If this is the case on your car, then obviously this test is invalid.

2. The 02 sensors likely kick-in after the engine goes into closed loop state (i.e. after the engine is warmed up). Getting your engine to a warm state may be a challenge if idle cannot be maintained.

CadiJeff
12-23-07, 02:10 AM
in my experience I would say you have a fuel pressure leak inside the intake manifold, fuelpressure reg. or fuel inj.

in answer to another question, no there is no MAF screen on a 94

I may be wrong but I saw no mention of plugs,wires and coil packs being checked

I would also not rule out vacume leaks

enjoy:thumbsup:
Jeff

Ranger
12-23-07, 03:08 AM
One thing that I noticed while cleaning my throttle body was that I don't have a MAF screen like in these instructions:
It is actually an air flow straightener and should be on there. The lack of it could be sending false signals to the MAF.


Is the throttle plate the same as the throttle body blade? (I think so but I want to make sure)
Yes, one in the same.


I tried to search for a picture of the ISC motor and location. Can you tell me where to find it?
Sounds like you already found it. It is a motor mounted on the side of the TB that has a plunger in contact with the throttle lever.

Ranger
12-23-07, 03:11 AM
in answer to another question, no there is no MAF screen on a 94
Oops, maybe I stand corrected. Are you sure?

clarkz71
12-23-07, 10:59 AM
Oops, maybe I stand corrected. Are you sure?

96 is the 1st year for the MAF sensor. Only OBD II N* cars have them.

Ranger
12-23-07, 12:50 PM
I learn something new every day. Thanks Clark.

clarkz71
12-23-07, 01:21 PM
I learn something new every day. Thanks Clark.

Hey, it's not very often I get to trip you up!!;)

whoaskew
12-25-07, 04:49 PM
Another thought comes to mind. If it only starts with your foot on the pedal, then the throttle plate is completely closed and the engine will never start as it is completely choked. Watch the ISC motor when the key is turned on. Does it activate and extend to open the throttle plate a bit?

I turned the key to the "on" position and the ISC motor did nothing. The throttle plate stayed shut, so it looks like that will be the first thing that I replace.

Ranger
12-25-07, 05:38 PM
Make sure that it is getting power before replacing it. When the key is on and you press on the plunger, does it retract?