I'm having problems with my car it keeps reving up between 2 1/2 and 3 grand and sounds like its cutting out but it only does it on the freeway and not all the time. It also revs up to a grand then dies when I'm just idling. Can anyone help me figure this out? Thanks
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1988 740 Turbo
Started by Big Jx253x, Nov 11 2009 08:33 AM
5 replies to this topic
#1
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Posted 11 November 2009 - 08:33 AM
#2
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Posted 12 November 2009 - 05:02 AM
Well it doesn't sound like anything I've heard of before, not sure how it could rev up & down without diver induced throttle oscillation while in gear and cruising down the highway, though I have seen cruise control do that when there is a cruise related vacuum leak.
Odds are it is some sort of intake leak, or a possible fault related to the IAC, maybe a bad or loose IAC hose. You might also inspect the wiring for the distributor, maybe some sort of a fault with the hall sensor.
You might read through some of these:
http://www.brickboar...nceSymptoms.htm
and see if anything fits your symptoms.
Odds are it is some sort of intake leak, or a possible fault related to the IAC, maybe a bad or loose IAC hose. You might also inspect the wiring for the distributor, maybe some sort of a fault with the hall sensor.
You might read through some of these:
http://www.brickboar...nceSymptoms.htm
and see if anything fits your symptoms.
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Posted 17 November 2009 - 07:41 AM
Now its gotten to the point to where I can barely hit 60 and all it does is backfire.
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Posted 17 November 2009 - 08:36 PM
If the backfire is from the intake/engine compartment, odds are you are running too lean due to an intake leak somewhere between the MAF sensor and the clyinder head. If the backfire is from the exhaust (like gun shots), odds are you have some sort of ignition system failure, which could be timing belt related.
You might want to check your timing belt marks.
http://www.threefatt...TimingMarks.htm
Line up the crank to TDC, pull the fan off the water pump, walk the pump pulley forward off the pump, no need to loosen the fan belts. Then pull the top timing belt cover, use a flash light to look down inside the lower cover to verify the crank timing mark.
You might want to check your timing belt marks.
http://www.threefatt...TimingMarks.htm
Line up the crank to TDC, pull the fan off the water pump, walk the pump pulley forward off the pump, no need to loosen the fan belts. Then pull the top timing belt cover, use a flash light to look down inside the lower cover to verify the crank timing mark.
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Posted 20 November 2009 - 09:59 AM
Ok thanks it is an exhaust backfire. I'm going to check the timing in the morning. The other day I went to drive it and it was running fine then died after about 10 min of driving. It wouldn't start again it would just turn over. I checked for spark and wasn't getting any after messing with it for aabout a half hour I was calling it quits so I could go to work and decided to try it one more time to try to get it home and it started right up and drove home. could it be a coil?
#6
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Posted 20 November 2009 - 10:54 PM
The most common possibilities would be either the radio suppression relay (RSR), or it could be a failing ignition module.
The RSR is fairly easy to test, normally there is an identical relay right next to it that is for the radiator electric pusher fan, just swap the relays. You might pop the cover off the relay and look for any cracked or failed solder joints and re-solder them. Otherwise it's a simple single pole single throw relay, any standard generic automotive type relay will work in it's place, although you would want to change the socket to a matching generic socket.
The ignition module is the same part as used on all '89+ 240s, 740s(non regina), 940s(non regina), as well as earlier 740s going back to '85 IINM, so finding a used one shouldn't be a stretch.
Otherwise it may be a failure with the wiring to the distributor, another common failure point. Or a possible fault with the hall sensor in the distributor.
The RSR is fairly easy to test, normally there is an identical relay right next to it that is for the radiator electric pusher fan, just swap the relays. You might pop the cover off the relay and look for any cracked or failed solder joints and re-solder them. Otherwise it's a simple single pole single throw relay, any standard generic automotive type relay will work in it's place, although you would want to change the socket to a matching generic socket.
The ignition module is the same part as used on all '89+ 240s, 740s(non regina), 940s(non regina), as well as earlier 740s going back to '85 IINM, so finding a used one shouldn't be a stretch.
Otherwise it may be a failure with the wiring to the distributor, another common failure point. Or a possible fault with the hall sensor in the distributor.
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