Sputter is back... 88 L98 Automatic....HELP?
Thread Starter
Instructor
Joined: Jun 2003
Posts: 126
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From: Markham Ontario
Sputter is back... 88 L98 Automatic....HELP?
Okay....some months ago, I had what I thought was a fuel pump issue. Changed it and haven't have a problem since. NOW, it's back.
The shift light comes on and a small D with a circle around it in the center of the tach comes on.....at that point, it sputters and back fires.... Can't figure it out.
I've changed the fuel pump 2 months ago due to this problem and it was fine, until now.
Suggestions?
Fuel pressure it fine....had it tested...... anything else?
ECM perhaps?
The shift light comes on and a small D with a circle around it in the center of the tach comes on.....at that point, it sputters and back fires.... Can't figure it out.
I've changed the fuel pump 2 months ago due to this problem and it was fine, until now.
Suggestions?
Fuel pressure it fine....had it tested...... anything else?
ECM perhaps?
Team Owner
Joined: Jul 2003
Posts: 24,650
Likes: 8
When Iread the post it sounded like you had the Doug Nash 4+3, and that the car was asking you to shift into OverDrive....but you say it is an auto tranny...so I really am at a loss here....
possbily a short in the wiring harness. Possibly the harness was the same for the auto and manaul cars. and yours has a short in the unused manaul tranny wiring somewhere...
this is all a guess...because thats really weird.
possbily a short in the wiring harness. Possibly the harness was the same for the auto and manaul cars. and yours has a short in the unused manaul tranny wiring somewhere...
this is all a guess...because thats really weird.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
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From: seattle WA
I've had that same problem. 87 auto, while driving in D, sometimes the upshift light-the big arrow pointing up will flash, and sometimes the O with the D in it will flash-I know it's supposed to flash if the computer wants you to shift-for fuel economy. I also replaced my pump and filter-it came on a few times after-but seems to have gone away. I don't have any miss issues though.As a matter of fact-you and I talked via email about this-funny since my car came back from the body/paint shop it hasn't done this-and it's running great.
Last edited by rick lambert; Nov 3, 2004 at 09:56 AM.
Thread Starter
Instructor
Joined: Jun 2003
Posts: 126
Likes: 7
From: Markham Ontario
Okay, it still does this...replaced the ignition module, fuel pump and relay. Still.... the D with a circle comes on, and it starts sputtering.
Does Anyone have any suggestions as to what this may be?
Does Anyone have any suggestions as to what this may be?
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
First pull any stored codes; the answer may be in there.
I think the shift light comes on because the engine is losing power very near the shift point so the A4 isn't shifting quickly enough so the ECM is alerting you.
Put a fuel pressure gauge onto the Schraeder, lay it on the windshield under the wiper blade and monitor pressure when the problem occurs.
BTW, the FP relay only supplies power to the FP during the first 2sec that the ignition switch is turned on to prime the fuel rail. Thereafter the FP only receives power through the oil pressure switch on the stalk behind the intake base to the left of the dist.
I think the shift light comes on because the engine is losing power very near the shift point so the A4 isn't shifting quickly enough so the ECM is alerting you.
Put a fuel pressure gauge onto the Schraeder, lay it on the windshield under the wiper blade and monitor pressure when the problem occurs.
BTW, the FP relay only supplies power to the FP during the first 2sec that the ignition switch is turned on to prime the fuel rail. Thereafter the FP only receives power through the oil pressure switch on the stalk behind the intake base to the left of the dist.
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by 65Z01
BTW, the FP relay only supplies power to the FP during the first 2sec that the ignition switch is turned on to prime the fuel rail. Thereafter the FP only receives power through the oil pressure switch on the stalk behind the intake base to the left of the dist.
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Team Owner
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From: SE NY
Cruise-In II Veteran
CFI-EFI, thanks for the correction and I apologize for putting out incorrect info. I had read somewhere that only the oil pressure sw provided power to the FP, as a safety feature in the event of oil pressure failure. But my '88 GM Shop Manual confirmed your statement.
Sooo, I hooked a DMM across ALDL pins A & G to verify FP relay operatoin and got no voltage reading during cranking or running, not until just after I turned off the ignition key. This proves that the FP relay is indeed closed during cranking and normal engine operation. The ECM only turns off the FP relay if you don't start the engine within 2sec of turning on the ignition key.
Sooo, I hooked a DMM across ALDL pins A & G to verify FP relay operatoin and got no voltage reading during cranking or running, not until just after I turned off the ignition key. This proves that the FP relay is indeed closed during cranking and normal engine operation. The ECM only turns off the FP relay if you don't start the engine within 2sec of turning on the ignition key.
Race Director
Joined: Sep 2000
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From: The Top of Utah
Exactly! Many think that the oil pressure switch is a "safety" in case of a roll over or other loss of oil pressure. It isn't. It is a "safety" only in the event of a fuel pump relay failure. You and I both learned this the same way. A few years back, I made a statement consistent with the "common knowledge", and was corrected. I dug into my service manual to mount a comeback and learned I was wrong. Since then, I have burned out the priming circuit in my ECM. Knowing how it really works made my patch job much easier.
RACE ON!!!
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Thread Starter
Instructor
Joined: Jun 2003
Posts: 126
Likes: 7
From: Markham Ontario
Okay now, I am thinking it's a tranny issue. Since I've had the car, I've yet to touch the tranny. Perhaps the fluid needs to be flushed, and therefore, can't provide enough pressure to shift, therefore, sending an error code........Does this make sense at all??
Le Mans Master
Joined: Oct 2003
Posts: 6,130
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From: seattle WA
I'm more inclined to think engine component rather than tranny. Really don't know what cured my up shift light problem-like yours, but I didn't have a miss or sputtering. Hard for me to believe a tranny issue would cause it to back fire. Have you checked your injectors?
Burning Brakes
Joined: Aug 2001
Posts: 1,146
Likes: 9
From: Troy Ohio
Hey me too......
I get the same od light and the big arrow. This occurs occasionally when i'm cruising down the highway at speed. I know i am in overdrive but I cant figure out what is causing this. Speed and rpms look alright. The only thing different is mine does not sputter or run bad, stilll runs aok.
Advanced
Joined: May 2001
Posts: 82
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From: Trollhattan,Sweden
I´ve got an -88 w auto, had a similar problem four years ago. I suddenly had problem to start the car, when it started, the engine ran really bad, sputtering and backfiring. Funny about the shiftlight... it flashed when I was standing still. I drove to a workshop in a state of mild panic (I had owned the car a couple of months). They replaced the ECM, and everything was fine. If you have the possibility, switch ECM with another car to rule it out. (A friend of mine has a Firebird, last summer it ran bad when hot. We logged it, and discovered that it wouldn´t stay in closed loop for more than a minute or so. We replaced a lot of various sensors with no result. We put his ECM in the Corvette, and it showed the same problem. He replaced the ECM...voila´!)
Burning Brakes
Joined: Aug 2001
Posts: 1,146
Likes: 9
From: Troy Ohio
Yeah could be
The ecm may be the reason. I had to replace the ecm and I didnt see this problem for a long time. Now i see it once in awhile. My car has a history of eating ecms, about one every two years, says the previous owner (brother). This particular ecm is about 2 yrs old.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
WOW! sounds like the last few responses might be the answer. Like I said before I didn't have the sputter (miss) just the upshift light and it's probably coincidence-but because I had a temporarily stuck valve in the tranny (which they fixed with a hammer) I decided to have the transmission serviced (fluids, filters etc.) I haven't noticed the upshift light-of course I did the fuel pump and filter like you too. Has the tranny ever been serviced?
