1990 missing 1500-2000rpm
Thread Starter
Racer
Joined: Jun 2011
Posts: 497
Likes: 1
1990 missing 1500-2000rpm
So when I bought the car I was told it was the injectors. I believed him because they were the multec stock. So I replaced them and the replaced them again with boschs. After a plug change and injector change its still doing it.
I've tried to do some reading on this problem, but needed to replace my heater core (NEVER AGAIN!!!) and my clutch master so for a few weeks the miss problem was put behind some other priorities, as I don't drive it but occasionally.
I've read that the pigtails could short out or possibly a weak head gasket could be the culprit.
Im not throwing any codes and its extremely aggravating. Where should I start?
(1990 6sp z51)
I've tried to do some reading on this problem, but needed to replace my heater core (NEVER AGAIN!!!) and my clutch master so for a few weeks the miss problem was put behind some other priorities, as I don't drive it but occasionally.
I've read that the pigtails could short out or possibly a weak head gasket could be the culprit.
Im not throwing any codes and its extremely aggravating. Where should I start?
(1990 6sp z51)
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
Its worth the time and trouble to go thru the electrical harness. I've solved many misfires by simply cleaning the jumper post wires that supply power to the harness,. ECM and all eng accessories.
Make sure all grounds are clean and tight. The most important are the set of 5 on a bolt near or above the oil filter. On the block or the bellhousing.
Go thru the dist and make sure the small pins & plugs inside are good and there are no pinched wires inside the dist cap. Make sure the ICM is bedded in heat sink grease.
if all that is done and it still has a misfire, I'd change out the ICM after following the FSM flow chart for this problem. The FSM is never wrong if you do as it ask.
Make sure all grounds are clean and tight. The most important are the set of 5 on a bolt near or above the oil filter. On the block or the bellhousing.
Go thru the dist and make sure the small pins & plugs inside are good and there are no pinched wires inside the dist cap. Make sure the ICM is bedded in heat sink grease.
if all that is done and it still has a misfire, I'd change out the ICM after following the FSM flow chart for this problem. The FSM is never wrong if you do as it ask.
Thread Starter
Racer
Joined: Jun 2011
Posts: 497
Likes: 1
Update. I noticed today it is running rich (haven't ran for this long in a bit) but it is noticeable. Seems to only miss under slight load. When im about 1/4+ into the throttle there is no miss. When im completely off the throttle there is no miss. When im at a slight cruise throttle (3-6th gear) there is the miss.
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
Is your cooling system acting normal?
When I fought my 1500-2000 miss it turned out to be a leaking head gasket..
Make sure you check your Spark plug connections closely, I've had these back off in the past, and cause a miss. If you remove the boot and look inside of it and find a grey powder build up this could indicate an arcing. You can also mist the wires while the engine is running in a dark garage and look for any arcing.
just a few...
When I fought my 1500-2000 miss it turned out to be a leaking head gasket..
Make sure you check your Spark plug connections closely, I've had these back off in the past, and cause a miss. If you remove the boot and look inside of it and find a grey powder build up this could indicate an arcing. You can also mist the wires while the engine is running in a dark garage and look for any arcing.
just a few...
Burning Brakes
Joined: Jun 2003
Posts: 849
Likes: 1
From: dubuque iowa
I have always belived in keeping diagnostics simple as possible which is to simplify as much as possible ignoring that its fuel injected and computerised and work your way up through the basics first before diving into the more complex extreams.
now thinking back to basics it seems to me that the rule was that plugs could cause a miss but at idle or all the time and that it is bad plug wires that miss under load.
would be nice if you could test this in a stationary spot, can you put it under enough load just putting it in drive with the brakes held tight and slowly pushing the gas? if so would be easy to test the firing of each wire one by one then move on with diognostics from there..
just my 2cents
now thinking back to basics it seems to me that the rule was that plugs could cause a miss but at idle or all the time and that it is bad plug wires that miss under load.
would be nice if you could test this in a stationary spot, can you put it under enough load just putting it in drive with the brakes held tight and slowly pushing the gas? if so would be easy to test the firing of each wire one by one then move on with diognostics from there..
just my 2cents
Thread Starter
Racer
Joined: Jun 2011
Posts: 497
Likes: 1
So I replaced my Coil, cap and rotor and it ran great... for about twenty miles. Then it started missing again, only under slight load. I did a pressure test. 44lbs key turned. 36-37 at idle. So im gonna swap out plugs then update.
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Thread Starter
Racer
Joined: Jun 2011
Posts: 497
Likes: 1
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