Need help with 1990 with terrible miss
Thread Starter
Le Mans Master
Joined: Aug 2000
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From: Airport Cruise-in 1 Veteran Airport Cruise-in 2 Veteran
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Need help with 1990 with terrible miss
Hi Folks,
I have a friend with a 1990 that has me stumped and I need your help BADLY! All was good until he got on the gas. He says he got on the throttle hard and it started to run like crap. It idles rough like he has a miss and stays that way throughout the driving range. Codes 21 and 34 popped up. I thought maybe he needs a prom upgrade due to his mods but he reminded me that it was running fine before. It just happened all of a sudden.
He's done plugs, wires, cap, rotor and fuel filter and has not cleared the problem. We tested the TPS and get no reading. We even checked a few other TPS's that I have in my little Dr. bag and none of them had a reading. He tested the wire from the TPS to the ECM and it checks OK. I checked all the vacuum lines and everything appears to be fine. Nothing seems to be unplugged. No codes have stored since the original ones were erased.
What else should we look for? Any help would be very appreciated! :blueangel:
-John
I have a friend with a 1990 that has me stumped and I need your help BADLY! All was good until he got on the gas. He says he got on the throttle hard and it started to run like crap. It idles rough like he has a miss and stays that way throughout the driving range. Codes 21 and 34 popped up. I thought maybe he needs a prom upgrade due to his mods but he reminded me that it was running fine before. It just happened all of a sudden.
He's done plugs, wires, cap, rotor and fuel filter and has not cleared the problem. We tested the TPS and get no reading. We even checked a few other TPS's that I have in my little Dr. bag and none of them had a reading. He tested the wire from the TPS to the ECM and it checks OK. I checked all the vacuum lines and everything appears to be fine. Nothing seems to be unplugged. No codes have stored since the original ones were erased.
What else should we look for? Any help would be very appreciated! :blueangel:
-John
Team Owner
Joined: Dec 2000
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From: SE NY
Cruise-In II Veteran
Re: Need help with 1990 with terrible miss (War Machine)
The Code 21 (TPS too high when air flow is less than 15gm/sec) combined with Code 34 (MAP signal too high when TPS greater than 1.5Vdc) might point to a bad MAP sensor.
A scan tool would tell the story.
A scan tool would tell the story.
Team Owner
Joined: Oct 2000
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St. Jude Donor '08-'10
Re: Need help with 1990 with terrible miss (War Machine)
Make sure that the bolt that holds the distributor from turning is tight. If the bolt loose and you get on the gas hard it can turn a little at a time and you know the rest of the story.
Thread Starter
Le Mans Master
Joined: Aug 2000
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From: Airport Cruise-in 1 Veteran Airport Cruise-in 2 Veteran
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(65Z01)
Thanks! We'll check into that. :)
joecaver, we haven't done the timing yet due to the TPS reading 0.00. Will we still be able to accurately set the timing like that?
joecaver, we haven't done the timing yet due to the TPS reading 0.00. Will we still be able to accurately set the timing like that?
Melting Slicks
Joined: Apr 2002
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From: down that one road next to that big tree
Re: (65Z01) (War Machine)
corvette0096 has a spare map sensor if you need one, also keep an eye on your plug wires, more misfires come from leaky wires that are gummed up with oil
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Le Mans Master
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From: Airport Cruise-in 1 Veteran Airport Cruise-in 2 Veteran
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Thanks again for the help. Well here's an update. We set the timing, checked the TPS again and the MAP, both seem to be fine. I think his code 21 is from that silly throttle performance switch. :crazy: We decided to change out the ECM and it ran worse. We're beginning to think it's the fuel pump by the way it was bucking back and forth. I don't really know what a failing fuel pump is like on a C4 so I could be wrong.
Thread Starter
Le Mans Master
Joined: Aug 2000
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From: Airport Cruise-in 1 Veteran Airport Cruise-in 2 Veteran
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Re: (War Machine)
Thanks for the suggestions! :cheers:
It turned out to be one fuel injector stuck open. Also it is that doggone throttle performance switch that set a code 21. I really wish the parts folks would stop selling that thing. :mad
It turned out to be one fuel injector stuck open. Also it is that doggone throttle performance switch that set a code 21. I really wish the parts folks would stop selling that thing. :mad
