Dickinson County Comanche Posted May 23, 2022 Share Posted May 23, 2022 I’m at a loss here, I recently acquired a 2.5L 86’ for cheap that hadn’t run in a while and was missing its transmission. I’m happy to say it runs and drives now, but like absolute garbage. It’ll sit and idle, smooth, all day long. But if you try and rev it (above ~1000rpm or so) it will sputter and begin to backfire through the intake. It won’t die though, although the popping does get noticeably more stronger. I indexed the distributor 2 teeth back and it allowed a little throttle to be applied, but it’ll backfire through the exhaust instead of the intake. Here’s what I’ve checked so far: - Distributor timing - Compression ( #1 I didn’t check because it’s hidden behind the A/C compressor, #2 135psi, #3 140psi, #4 135psi) -CPS voltage -exhaust blockage (ran bad with exhaust not hooked up) I haven’t tested fuel pressure but I think it would be ok. New fuel pump and fuel filter were just put in so maybe a blockage in the line? I also have very little vacuum at idle, there’s some for the brake booster but none anywhere else and none of the dash vents work. It also does have a “high altitude” CPS in it for some reason so would that maybe cause it? I have an extra CPS for a 4.0 that I can toss in if it’ll work or not. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 23, 2022 Share Posted May 23, 2022 TPS adjusted? MAP readings up to spec? Vac lines secure and not damaged? Coolant normal? O2 working? Link to comment Share on other sites More sharing options...
fiatslug87 Posted May 23, 2022 Share Posted May 23, 2022 Could a stuck open EGR cause these symptoms? Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted May 23, 2022 Author Share Posted May 23, 2022 1 hour ago, eaglescout526 said: TPS adjusted? MAP readings up to spec? Vac lines secure and not damaged? Coolant normal? O2 working? I’ve checked the MAP with another I know is good and it’s made no difference. Coolant was good and it had no extra pressure or exhaust smell. Vac lines have been checked and I do not hear any leaking like I would. I haven’t adjusted the tps but I did plug in a good one on a TB I have laying around and it didn’t have any difference. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted May 23, 2022 Author Share Posted May 23, 2022 1 hour ago, fiatslug87 said: Could a stuck open EGR cause these symptoms? It definitely could. I’ll have to check it in the morning and see. Link to comment Share on other sites More sharing options...
gvthnks Posted May 23, 2022 Share Posted May 23, 2022 what do the spark plugs look like? Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted May 23, 2022 Author Share Posted May 23, 2022 1 hour ago, gvthnks said: what do the spark plugs look like? They looked good although maybe just a skosh toward the lean side. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted May 23, 2022 Author Share Posted May 23, 2022 10 hours ago, fiatslug87 said: Could a stuck open EGR cause these symptoms? EGR is bad but it was stuck closed. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 23, 2022 Share Posted May 23, 2022 That’ll do it. The solenoid will pull vac to open the EGR and if it can it’ll struggle to run. Link to comment Share on other sites More sharing options...
gvthnks Posted May 23, 2022 Share Posted May 23, 2022 3 hours ago, Dickinson County Comanche said: They looked good although maybe just a skosh toward the lean side. many a day, I've had this exact issue with an engine only to find out that under a load, the spark plugs, or ignition wires were leaking fire and it simply wouldn't rev. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted May 23, 2022 Author Share Posted May 23, 2022 3 hours ago, gvthnks said: many a day, I've had this exact issue with an engine only to find out that under a load, the spark plugs, or ignition wires were leaking fire and it simply wouldn't rev. The cap and rotor were kinda worn, I have new ones coming in tomorrow Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted May 24, 2022 Author Share Posted May 24, 2022 8 hours ago, Dickinson County Comanche said: The cap and rotor were kinda worn, I have new ones coming in tomorrow Hopefully this is it. I threw a spark tester on it and it loses spark then misfires, it doesn’t do it however when it’s idling so hopefully it’s just the cap and rotor being worn out. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted May 24, 2022 Author Share Posted May 24, 2022 New cap and rotor have done nothing. I tested the good ICM and coil from my 89 4.0 and it did nothing. It has very hit-or-miss spark at anything above basically idle. I’ve put in 2 CPS’s and neither of them have improved it any. I’m genuinely at a loss here. Distributor is in time, good plug wires, and all of the plugs have been gapped (minus cylinder 1, but I can verify that it’s firing) to spec. Distributor doesn’t have a major amount of play, and is on the correct tooth of the cam. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted May 24, 2022 Author Share Posted May 24, 2022 We’re talking a very low rpm here too, it’ll lose spark when the engine high-idles to warm up. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted May 24, 2022 Author Share Posted May 24, 2022 IMG_9194.MOV Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 24, 2022 Share Posted May 24, 2022 Mind posting a pic of the engine bay? Maybe I can see if something is out place. I also recommend a TPS adjustment just to rule it out as if it’s reading the position to dump more fuel in than what the engine can keep up with for the air ratio, it can throw things out of wack, and verify the fuel system is working properly like with pressure, no bad injector gaskets and fuel pump. I had the filter come off in the tank once and it made driving rough for me with loss of power. Has the fuel filter been replaced recently? Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted May 24, 2022 Author Share Posted May 24, 2022 34 minutes ago, eaglescout526 said: Mind posting a pic of the engine bay? Maybe I can see if something is out place. I also recommend a TPS adjustment just to rule it out as if it’s reading the position to dump more fuel in than what the engine can keep up with for the air ratio, it can throw things out of wack, and verify the fuel system is working properly like with pressure, no bad injector gaskets and fuel pump. I had the filter come off in the tank once and it made driving rough for me with loss of power. Has the fuel filter been replaced recently? The whole fuel system has been gone through. I have verified already that it is not something to do with the fuel system as it doesn’t rev even with me bottle feeding it gas down the TB. It has to be spark-related somehow as it is hit-or-miss when it revs up. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 24, 2022 Share Posted May 24, 2022 All terminals and contacts related to the spark system has been cleaned and shiny right? Could also be having an intermittent injector issue. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted May 24, 2022 Author Share Posted May 24, 2022 51 minutes ago, eaglescout526 said: All terminals and contacts related to the spark system has been cleaned and shiny right? Could also be having an intermittent injector issue. I just cleaned the main block ground to no avail. All of the grounds check out ok as well and they seem to be getting proper voltage (~12.01V or so) Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 24, 2022 Share Posted May 24, 2022 How do the connections on the starter relay look? We can always do a run down of the sensors to make sure they are supposed to be at their proper values. Link to comment Share on other sites More sharing options...
Ωhm Posted May 24, 2022 Share Posted May 24, 2022 Take that air bonnet (aka ADAPTER, Air Intake) off at the throttle body and make sure you're not starving on air. Look/make sure the throttle plate is moving. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted May 24, 2022 Author Share Posted May 24, 2022 1 hour ago, eaglescout526 said: How do the connections on the starter relay look? We can always do a run down of the sensors to make sure they are supposed to be at their proper values. I’ve checked every connection I can and they all seem ok. Which sensors should I try first? Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted May 24, 2022 Author Share Posted May 24, 2022 36 minutes ago, Ωhm said: Take that air bonnet (aka ADAPTER, Air Intake) off at the throttle body and make sure you're not starving on air. Look/make sure the throttle plate is moving. It’s something to do with ignition. It runs just as bad with the air intake on as it does when it’s off. I appreciate the help though. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 24, 2022 Share Posted May 24, 2022 Well we can check the injector and make sure it’s resistance is correct. Since it’s an 86 it’s gonna have a wide open throttle WOT switch, make sure that’s not stuck, EGR solenoid and TPS to start. You said the CPS is outputting correct voltage so we will leave it alone for now. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted May 24, 2022 Author Share Posted May 24, 2022 22 minutes ago, eaglescout526 said: Well we can check the injector and make sure it’s resistance is correct. Since it’s an 86 it’s gonna have a wide open throttle WOT switch, make sure that’s not stuck, EGR solenoid and TPS to start. You said the CPS is outputting correct voltage so we will leave it alone for now. I actually just tried to probe the CPS for the correct voltage and I got nothing. Could it be that the flywheel got a little bit rusty due to sitting out exposed when there was no transmission on it? Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now