What would cause this???
Thread Starter
Racer
Joined: Nov 2006
Posts: 420
Likes: 0
From: Sierra Madre California
What would cause this???
I'm a bit baffled. In the last couple of days my '88 has been exhibiting strange behavior. At idle and the first 25% of gas pedal it seems to run fine, but when I when I put my foot in it, it completely flattens out and won't accelerate at all; even missing a bit. When I let off of the gas, it seems to run OK again. Has anyone else experienced this? I would be very appreciative of any guidance.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
I would check your fuel pressure while running first..If you have a pressure gauge screw it to the fuel rail and lay it flat against the windshield so you can check the pressure while driving. Watch the gauge while you run through the rpm trouble area and see what readings you get...If its not the fuel pressure then you have to start testing to find out if this is being caused by fuel or spark. It could be quite a few different things causing this and you have to test to find out which one it is..This is where a factory service manual really comes in handy.....WW
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Thread Starter
Racer
Joined: Nov 2006
Posts: 420
Likes: 0
From: Sierra Madre California
OK, I bought a fuel pressure tester, connected it, and taped it to the windshield. Idle pressure is right at 38. When I got on it hard it still flattened out and started to miss & buck again, but at no time did the pressure gauge go below 30. With 24# injectors, I would think that this should be enough. When I let off the gas and drive gently, all seems normal. I've been assuming that it is a fuel delivery issue, but maybe it's a spark problem. I couldn't find anything in the FSM that addresses this symptom. Any ideas? This has me stumped.
Pro
Joined: Mar 2000
Posts: 658
Likes: 7
From: Perth Amboy New Jersey
OK, I bought a fuel pressure tester, connected it, and taped it to the windshield. Idle pressure is right at 38. When I got on it hard it still flattened out and started to miss & buck again, but at no time did the pressure gauge go below 30. With 24# injectors, I would think that this should be enough. When I let off the gas and drive gently, all seems normal. I've been assuming that it is a fuel delivery issue, but maybe it's a spark problem. I couldn't find anything in the FSM that addresses this symptom. Any ideas? This has me stumped.
Burning Brakes
Joined: Jun 2003
Posts: 1,079
Likes: 1
From: Niagara Falls ON
How old is your air filter? Poor air flow will cause the engine to run rich
If your fuel and air filters are old it can't hurt to change them. The cost of these are good insurance anyways.
Do you have a digital multi-meter to test the TPS?
Check and test anything that you can...that is the cheapest way.
If your fuel and air filters are old it can't hurt to change them. The cost of these are good insurance anyways.
Do you have a digital multi-meter to test the TPS?
Check and test anything that you can...that is the cheapest way.
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
another possibility could be the spark plug boots have backed away from the plugs, at idle and low power the arching is Sufficient to keep the engine running, under a load it's a whole differant story..
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
OK, I bought a fuel pressure tester, connected it, and taped it to the windshield. Idle pressure is right at 38. When I got on it hard it still flattened out and started to miss & buck again, but at no time did the pressure gauge go below 30. With 24# injectors, I would think that this should be enough. When I let off the gas and drive gently, all seems normal. I've been assuming that it is a fuel delivery issue, but maybe it's a spark problem. I couldn't find anything in the FSM that addresses this symptom. Any ideas? This has me stumped.
Dave
Team Owner
Joined: Jan 2003
Posts: 20,320
Likes: 248
From: Summerland B.C. Canada
If the FP at idle is 38 that would make sense as I had thought it should be 45 with key on engine off or the vac line to regulator disconnected with engine running. If you went down in pressure when you got on it you found the problem or one of them at least, the fuel pressure should have gone up to 45 psi not down to 30 psi. There may be other problems with ignition or other sensors but this is not right as you describe it.
Dave
Dave
Thread Starter
Racer
Joined: Nov 2006
Posts: 420
Likes: 0
From: Sierra Madre California
I relieved the fuel rail pressure via the schraeder valve, and turned the key on. Shouldn't I hear the fuel pump chattering to rebuild the pressure? I hear nothing. Does this tell me anything?
Burning Brakes
Joined: Mar 2006
Posts: 891
Likes: 18
From: Dayton Ohio
You might be better off trying a fuel filter change if it hasn't been done in a long time. Other than that I wouldn't start throwing parts at it unless you can get some data. Fuel pressure reading is a good start but if you can connect to your ECM and record data it will probably tell you where to concentrate your efforts.
Matt
Thread Starter
Racer
Joined: Nov 2006
Posts: 420
Likes: 0
From: Sierra Madre California
Yes, your point is well taken; I don't have the dough to get caught up into the "throw parts at the problem" cycle. Am I wrong in my assumption that I should be able to hear the fuel pump re-charging the fuel rail pressure? It seems to me that I used to ba able to hear it. What's making this particularly frustrating is that I have Turbolink 4.0, which would possibly tell me a lot if I could get it working. The problem is that it requires a serial port connection, which my laptop does not have. I bought the USB to Serial convertor cable that Ken Mosher (creator of Turbolink) recommends, but can't get it to connect. If anyone has any insight into this, it would be really helpful. Perhaps I should start a new thread to see if anyone has any insight into this Turbolonk issue.
Last edited by jesredvette; Jan 2, 2012 at 09:36 PM.