Still Stumbling, Running like poo....

Thomas A

Thomas A

Registered User
Well, the car I'm working on ('90 SC Auto) is still not driveable. It will start right up, and idle fine. However, when you go to drive it, it starts acting up. When you accelerate at all, at any amount, it just stumbles, backfires, and tries to die. It's totally undriveable. But as soon as you let off of the gas, it runs perfect. So maybe I just need to turn up the idle to about 2K and just drive it off of idle :D

I recently replaced the DIS and CAM sensors, and have checked the wires several times. I'm confident that is not the problem. I also pulled codes, and none came up.

I tested the TPS and it read within range. .5 closed and 4.5 WOT with nice movement inbetween.

I tested the fuel pressure tonite. KOEO, it read ~10lbs. with and without the vac line hooked up. Running, it read ~36lbs. When I would blurp the throttle, it would jump up over 40lbs pretty quickly. Does that sound normal?

So, that's where I'm at. I'm getting pretty frustrated with this car and am running out of ideas. Please Help!!!!

Thanks. Thomas
 
Your KOEO fuel pressure is low. It should be in the 35-40 psi range. KOER 30-40 psi .

Could be a dying fuel pump. Or you have a stuck open injector. Also could be EEC related, as in bad. Check all grounds and check the ground wire at the rear of the driver's head.
 
Hrmmm.. I thought it was kinda low. The fuel pump is a brand new 255LPH, so that is prolly good. However the eec was messed with. And the ground on the head, that is on the driver's side, right? Thanks!!

Thomas
 
See if it will hold fuel pressure for 60 seconds, by doing a KOEO. Next thing to do is a balance test with a code reader. The balance test is done after a KOER test, wait for last code, then goose the throttle.
 
Similar occurance happened to me on previous cars. (Not SC's)
One time it was simply a plugged fuel filter.
The other time it was the gas pressure regulator on the fuel rail.
 
I went out and worked on it some tonite. Here is what I found:

After running the fuel pump for 10 seconds, the pressure stayed up to 37-38 lbs for 60 seconds. So that should rule out an open injector, and one symptom of a bad regulator.

Took it out on a drive with the guage hooked up and pressure increased nicely lb for lb with boost, all the way up to 50lbs at 10lbs boost. That should rule out another symptom of the regulator or pump or filter.

I changed the filter anyway becuase it prolly needed it.

I then ran a KOER test, and it pruduced a 41, which reads to be Oxygen Sensor indicating system lean, right side.

Could a bad O2 sensor make a car run this poorly, or is there something else causing the O2 to malfunction??

Thomas
 
Thomas A said:
When you accelerate at all, at any amount, it just stumbles, backfires, and tries to die. It's totally undriveable. But as soon as you let off of the gas, it runs perfect.
I recently replaced the DIS and CAM sensors, and have checked the wires several times.
Click to expand...
Have you checked for vaccuum leaks? Especially if you've had the IC tubes or the SC top off the car, or done anything with the MAF.
 
I know for sure that it isn't a vac leak. It's totally different from that. I'm going to do a balance test tonite and see what I find out.

Thomas
 
Alright, I did a balance test tonite and came up with a problem on #2 and #3. I checked the resistance on the two injectors and they were fine. If it was a bad ground, then all three should of been failing. So, I thought it might be either a bad injector harness or a bad PCM. So I then checked resistance on the harness connectors and they were alright also. So, I don't have any idea where to go from here??? HELP!!!

Thomas
 
Thomas its possable that those 2 injectors are sticking closed. I dont mean totaly shut closed or not working at all. I mean the pintles action may be rough and sticky causing them not to react quick enough to the signals from the ECU. That would cause the engine to run lean on that bank.
 
I went out and unplugged the #2 injector, and it ran just the same. That says to me that the injectors on #2 and #3 aren't doing a darn thing. Sounds like it's time to change the injectors.

Thomas
 
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Thomas, looks like you are narrowing it down. If #2 and #3 are next to each other, see if the connectors are mixed up.

Also make sure the EEC is securely tightened. How was the EEC messed with, as stated in an earlier post? Does the EEC match the same year SC. On different year SC's the injector pins are different on the EEC.

Also see if you are getting around 5+ volts with a KOEO at the connectors. To check for ground is little harder, since the EEC fires the injectors by using grounding them. YOu can check by having someone crank it and check for a signal with a volmeter or a 12 volt test light.
 
I looked through the EVTM and made sure that the correct injector plugs where on the correct injectors. I also double checked the EEC and the ground to make sure they were good. The EEC was pulled from the same car as the engine and wiring harness, so that should be fine. I really do appreciate your replies. You've helped me out quite a bit. It's nice to be able to bounce ideas around and get good input.

Thomas
 
Well now WHoa there Thomas, I did'nt realize the engine,EEC ans wiring harness was transplanted from another car. That puts a whole new twist on things. I dont know if you have ever had this combo working right before or this is the first time your trying to get the bugs out of it.
You might want to backprobe each one of those 2 injectors while the motor is running to see if there is a signal getting to those injectors before you go buy new injectors.
 
Thomas,

Don't buy new injectors, I've got a good set of 30# injectors off a 93 SC....let me know if you want me to ship you a couple.

David
 
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