Yesterday while i was driving my car randomly shut off. So i pulled over put it in park and restarted it. It ran fine for about 2 minutes and then cut off on me again. This time refusing to restart period. This morning I went out and cranked her over and she fired up but will not idle. I have to keep my foot on the gas and she will rev and purr like a kitten on steroids. But she will not idle.

Also when i let her stall out the fuel pump re primes itself without me touching the key. So am I correct in assuming its my fuel pump.
(If so what is a rough time estimate on dropping the tank.)

On a side note is it possible its the oil pressure cut off switch)

 

The oil pressure switch is backup power, not a safety switch. It will provide power to the fuel pump when oil pressure is greater than about 7 psi, if the fuel pump relay is not already.

The pump will prime when you first turn on the key, and will also continue to run for about 3 seconds if the engine stalls for any reason other than the key being turned off.

Check your fuel pressure before just condemning the pump out of hand.

 

I have no way to check fuel pressure. It is to my knowledge that if the oil pressure switch reads to low it shuts the fuel pump off. But idk for sure. This car is my DD so I was looking for some ideas so I don't just go throwing money at the car which I don't have.

 

No. The oil pressure switch does nothing of the sort. Yank your fuel pump relay, and try and start you motor. Be warned, you will have to crank until oil pressure starts coming up. You will know exactly when it does too, as at that point, the fuel pump will kick on, and the engine will start.

You could drain all the oil out of your motor, and so long as the fuel pump relay was working, the engine would run until it seized. It simply doesn't care there isn't any oil pressure.

Wanna test the theory, without sacrificing your engine? Unplug the oil pressure sensor. The engine will still start right up, and run just fine.

 

Ploegi, is correct. When doing my tpi swap, I had to learn all the circuits and functions. The oil pressure switch is wired in parallel. When the motor is cranking and oil pressure reaches a predetermined point, the switch closes and the fuel pump runs. That way, if the fuel pump relay fails, the engine will still start once the oil pressure reaches about 6 psi. I'm not sure of the exact pressure at which this occurs.

 

So I had determined my iac was bad and once I replaced it. The car idled fine and was going amazing on the test drive until the end. It shut off when I slowed down again and refuses to restart. It will start on ether and I can keep it running with throttle. But the moment the rpms hit a certain level it shuts off it dies. It doesn't try to stay alive at all even opening the throttle. It is like all power is yanked from the engine.

Obviously something is heating up and just stopping. If it was the injectors in theory I wouldn't be able to keep it running by increasing the rpms. ( I would think it would be the same with the fuel pump)"I have checked the fuse by the battery.

I'm not sure what it is guys. I'm at a loss it's my DD.

 

What does fuel pressure look like?

 

I dont know I have no way to get to the store to buy a tester. I plan on getting one when I can.

Maybe I'm just thinking wrong but if it didn't have fuel pressure to run at low rpm how would it at high rpm?

 

At higher rpm, the O2 sensor has the most control over fuel mixture, at idle..... injector pulse-width is determined from tables..... so, if fuel pressure were low, it would be insufficient to idle the engine......

It's one of those things you check just to be sure.

If the car won't start, check and see if you are getting spark.

 

I just had a similar experience.. It progressively got worse over the course of 2 weeks.. Simple cough, then it would die but fire back up. Sometimes it would fire and run as long as I kept some throttle open... Sometimes not... I replaced the ICM, Pulse Coil, Fuel pump relay even the fuel pump... Each time it would run just long enough for me to think I'd pinned it down. Then it died,,, dead nothing.
Turns out it was a wonky ECM, the main computer was just erratic.


I'd also look at the FPR...

 

DemonYusuke, if this is your '91 and it still has the stock injectors, they are likely bad. Warm up the engine and measure the resistance of each injector. Those that are under 12 ohms are bad.

RBob.

 

They are not the original injectors. I even just replaced one that was bad. I will ohm the injectors just in case.

I can get the car started after it has been sitting but it will die at idle after a few minutes if I don't hold it open. After that it takes ether to start it.

I wish there was a easy way for me to test my ecm. It has given me a code 42 since I have had the car and I have replaced everything involved but the ecm

 

Okay so I got the fuel pressure tester.

it reads 42 on first prime but it quickly drops to 35.

on cranking its 42 and running its 35 and very jumpy when i rev it.

I will have a video link soon.

 

Link to the video

 

Im not sure why it would lose fuel pressure after prime, without me starting it? This was one a few rare times it would stay idling for more then 2 seconds.

 

Does it run any better if you disconnect the vacuum line from the fuel pressure regulator? (and plug it.....)

 

I will check tomorrow

 

Okay When i plugged the vacuum line it gives me a solid 42 43 psi while its idling but it still randomly shuts off after 10 15 seconds or so. the Fuel psi doesnt drop either.

 

With it dying while having sufficient fuel pressure to run, would that lean more towards the ecm shutting it off, or vats possibly icm?

 

VATS shouldn't do that... I'd swap the ICM $45 out... If that doesn't do it, then the ECM $100

 

I don't know what it is, I'm about fed up with this stupid efi crap. If a ar is getting fuel air and spark it should run. Bit mine is not it is so dumb. If I don't figure out something soon I'm just gonna sell it.

 

Will it restart immediately after it quits?

 

OK, as even replacement Multec's are going to fail.

Try another ECM, be sure to retain the MEMCAL from the one you have. A quick test of the ECM is to rap on it while the engine is running. If the way the engine runs changes the ECM is bad.

RBob.

 

Changing the ECM is one of the least expensive, cleanest, easiest to do... Just make sure you use some sort of non marring plastic pry to separate the plug from the box as you hold the locks open... And be gentle when you swap the PROM. 25 year old plastic isn't very forgiving.
I wouldn't sell it for a song and let someone else fix it for $100...

 

Sometimes it will other times it won't start for 2 hours or more. But once it is started it dies at closed loop. I checked my o2 sensor and tried a replacement with no luck.

My injectors are bosch not multecs. All the injectors ohmed where they should.

The only thing I can think to do is buy an aldl cable and hook it up to my laptop and see what is happening myself. I'm not good at reading the data but I know plenty of people on this forum can help. I will try pulling the ecm and reseating the prom and checking the connections.

I don't plan on selling my car I love my car but I hate the stock efi.

 

So interesting development, I restarted it after disconnecting the 02 sensor. It died at closed loop but I restarted it and held throttle until closed loop activated I then let it idle Down and to my surprise it idled and did so for over 5 minutes. I then hit the throttle and let it idle down again and it died. I restarted it again and it idled fine until I hit throttle and let it idle down again. This time it won't restart again.

I'm not sure what's going on once again lol.

 

It shouldn't be able to go into closed loop with the O2 sensor disconnected......

I think plugging in, and monitoring the engine till it does it trick has the potential to be very enlightening.

 

I plan on it just have to wait until payday then wait for shipping

 

subscribing..

 

I ordered the cable just waiting for it to arrive.

 

Still waiting for my cable to arrive it's been over a week.

 

I got the cable finally. I work all week so I should have the results sometime this weekend

 

Why do you think it is fuel related and not spark? Bad coil, bad sensor?

 

Okay guys its been awhile but here is a really crappy video of some of the data tables. Tells me my 02 is bad but for some reason the computer see's my timing at 21 when its set to 8.

 

Heres a different look thats easier to read. This is when it shut off.

 

Just to clear a few of the stooped questions out of the way......
1. The 6-8 Degrees BTDC was set with the EST disconnected?
2. No chance your Harmonic balancer has slipped?
3. You don't have the Fan coolant sensor plug swapped for the detonation sensor?

I found the ACDelco O2 sensor is better than the Bosch...

Also, How did you get all of those parameters up on TunerPro? I can only get a few?

 

1. Yes
2. It appears that it has
3. No

$8D Bin and data stream file from tunerpro website. Along with a xdf file from code59 website is what I'm running.