Fuel delivery problem?

[prariedom]

Okay, I'm totally stumped and running out of ideas and money here!

 

Basically, the best I'm getting is the engine (3.1) in my '90 Lumina starts for about 2 seconds, then either dies outright, or kinda diesels and shakes hard, then stalls. Starter fluid or carb cleaner helps a little. Two months ago she wasn't running at all and at that time I had to replace the crumbling plug wires and old plugs with 8mm GM wires and platinum plugs; I was able to verify that the coil packs and ignition module were within specs and functioning, there appears to be a nice bright steady spark. I was verifying that the injectors were getting signal from the ECM with a noid light when it started running...for about a month it would run, but hesitated then jerked and took off when you started from a stop, otherwise it seemed to have good acceleration. On the other hand, I found and repaired a huge vacuum leak on the line that goes to the HVAC/Cruise/etc. but it still acted like it leaks; if you ran at a steady rpm (like highway cruising) the brakes would act like they had no vacuum, be flat. The night before Thanksgiving, my wife and I were out for dinner and it would not restart. The next day it started, only made it 1/2 mile, and died.

 

Since then, I checked the wiring harness and have not yet found problems; changed the fuel filter, replaced the MAP sensor (still getting codes 33 and 34, no MAF sensor on this car); and I have 40 lbs at the fuel rail, able to pump 1 pint in 25 seconds (30 is minimum), so I know I have enough fuel.

 

With a vacuum pump, I can pump the system to 50 psi and it holds indefinitely. With the vacuum gauge installed and a fuel pressure gauge at the rail, I get 15 lbs pressure initially but then it drops to 2-3 pounds once the motor starts dieseling; the fuel gauge starts at 40 psi, drops a smidge when it first runs, then the needle vibrates rapidly when the dieseling begins; when the motor stalls the pressure actually goes up to 46psi.

 

This car had the motor itself replaced at 36k with a 1994, the electronics appear to be origional, and it supposedly has 87k, an old couples car. Of course I can't check the EGR, it's digital.

 

Any help?

 

Bruce

[mfewtrail]

The fuel pressure readings you mentioned sound normal to me. Both of the codes you mentioned for the MAP sensor can be triggered by a bad ECM(engine control module). Here's a diagnostic flowchart for one of the MAP sensor codes, it should help you rule out the ECM.

 

[White93z34]

i'd say your fuel pump is dieing, you should get alot more then 15 psi. and on a 1990 i believe you should be useing a vaccum EGR, not a digital.

[mfewtrail]

i'd say your fuel pump is dieing, you should get alot more then 15 psi. and on a 1990 i believe you should be useing a vaccum EGR, not a digital.

 

I'm pretty sure he meant to type "15 in.hg"(vacuum) there, not psi...look at the other "psi" readings in comparison.

[Robby1870]

i'd say your fuel pump is dieing, you should get alot more then 15 psi. and on a 1990 i believe you should be useing a vaccum EGR, not a digital.

 

That depends. My STE has a digital EGR, but I think TGP's in 90 had vacuum EGRs? Maybe 90 was a crossover year for EGRs?

[gimper]

Yea 90 had both vacuum and digital EGR. Don't know if its car specific or if it's VIN related i.e. when during the year the car was made. My service manual for my 90 International doesn't mention a vacuum one while my wifes 90 TGP has a vacuum egr. Looking at parts for the EGR during 90 and you always get to choose between vacuum or digital. Looking at the diagnostic data stream and it looks like it changed half way through the 90 model run.... go figure...

 

Cheers Gimper

[prariedom]

Hmm. Sounds like I need to hunt someone down with a scan tool. MAP sensor A-C is 5vdc, but b-c is only 3.5 vdc at the start, dropping to 1.5 vdc - much lower than the chart. I might see if I can get the kids next door to let me tear apart their Lumina and borrow the ECM, to see if the problem clears up before I go out and buy one - the wife is a motorhead like me, they got this Lumina because she wrecked her '69 Chevelle on the way here from Florida (new job). It's a '91-'94, but I think it should work.

 

Definitely a digital EGR, same as the one my Corsica had, you can't just play with the vacuum diaphragm to see if it's working. I also tried swapping out the relay today, no dice; it still runs two seconds before it begins to freak out or stall out. I don't have a tach but I'd guess I'm turning around 200 rpm before it stalls, and if you try to give it any throttle, it dies outright. I noted the wiring to the MAP sensor is shared with the TPS, which appears to act up - so perhaps that's a clue.

 

Hey, I like old cars, they're just as enjoyable as a new one, and much cheaper. Besides, there's the pride that comes from resurrecting a car, and the respect you get from people who know you can do it

 

Chevys we've owned between us and our family-

 

'65 Impala SS, 69 Impala, (3) '69 El Caminos, '70 Chevelle, '74 Vega GT Wagon, '75 Vega (231 V6), '74 Impala, '75 El Camino, '77 El Camino, '79 Malibu wagon, '87 Celebrity 4 door 2.5, (3) Celeb Euro wagons 2.8, '94 Corsica 3.1, '94 Caprice LT1

 

Also: '90 Regal, '78 Cutlass Calais (403 V8), '86 Ciera wagon 2.5; a '65, '70, '73, '77, '84, '94 Olds 98's, '84 Delta, (2) 1990 S10s

 

Cheers! Thanks for the help. I'll keep updated.

 

Bruce