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losing power after 4000 rpm

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iron bird

10+ Year Contributor
166
0
Nov 7, 2008
Beaver Falls, Pennsylvania
i have a 92 gsx 6 bolt and im stumed on what else to try. First im running 9 psi wastegate routed straight to j pipe. the car runs perfect to 4000 rpm then just no more power. i did a boost leak test and fixed my only leak at the throttle body seals. im running 93 octane gas. everything is stock except for maf translator. compression is 160psi in every cylinder. replacing fuel filter tomorrow any other suggestions?
 
Did you have any recent shorts or anything? Check your ecu. Make sure that are no burn marks on the board. That will cause this problem. You my have a timing issue as well?

You need a little more info on what happen right before your car started having this problem
 
noticed after my alternator went bad. but im gonna check timing i just got the car and it has new timing belt and water pump it could have been doing this before and i just didnt notice like i said i just got the car and really never got on it before alternator went.
 
put stock maf on and now pulls to around 5000 rpm, but now i have a horrible stutter when first started and cold gonna try another boost leak test suggestions?
 
What spark plugs are you running? The NGK BPR6ES gapped at .028 is recommended. You shouldn't Boost the car until its warmed up at least not full boost. Do you have the same problem when its warm? Another thing to check is your TPS TPS Adjustment. Have you checked your ECU?
 
Last edited:
Do you have anything to log with? Sounds like timeing is being pulled. Try to find a good 1g maf and install it without the translater.

+1

We need to know a little more about what's going on. Is it more of a misfire, or does it feel like it's pulling timing and there's just no power? Check your plugs and wires. Weak ignition could be causing you to blow out spark when you're boosting.
 
there was a guy with a similar problem who had his ecu checked out by a shop. his culprit was leaking caps. take a look at your ecu and see if you can find any brown or black burn marks on the board.
 
Plugs are brand new bpr6es and new Ngk wires. Going to pull ecu and check tps today. Car only does when cold I'm not trying to boost and when I boost the car pulls to 5000 rpm then feels like your free reving it.
 
its defanitly not the clutch that was my besat way of explaining it. it pulls to 5000 rpm then pulls no more.
 
Ok, I understand. What where the results of your second BLT? This is kind of tough without seeing a log. If you have checked out everything that has already been mentioned and all is good the next thing would be your knock sensor. It sounds like its pulling timeing at 5000 so the ECU is seeing knock. You say its only doing this when its cold so when its warm it pulls to redline?
 
no it the same cold or hot. its stuttering really bad and has no power at all for the first 5 mins of driving with led me to believe a boost leak and it running fine once the computer compensates for the leak. testing tonight hopefully didnt get a chance yesterday.
 
just did a BLT and my TB shaft seals are leaking ordering some tonight
 
A restriction in the fuel system or weak fuel pump will cause a lean detonation and therefor create knock that results in retarded timing levels. So take that into consideration as you try to monitor your knock signal for diagnostic help. These are all good places to look for the culprit causing this issue. I am just saying to watch closely because sometimes one issue can cause two or three other things to look or act a little weird. Good luck and let us know what you find?
 
I agree with the possibility of a fuel delivery problem i.e. fuel pump,FPR, fuel filter. The filter should be replaced and the fuel pump rewired. Once the boost leaks are fixed we will see what happens. check this out Dataloggers if you get and extra 100 bucks it is one of the best investments you will make for your car.
 
fixed tb seals and now leaking at injectors could this cause a lean situation?
 
a leak there will be rich when in boost and lean in vacuum. both rich or lean can cause knock.
 
starting to sound like my problem is these dumb leaks! Stoping at napa tomorrow to get the injector rebuild kits then we will find where ever else i am leaking from ### i guarantee somewhere.
 
Sounds like you are on the right track. Anothe place to look is the connections to the SMIC the in and out of the IC are known to corrode. You can use some J.B.Weld to fill any pitting in the IC.
 
Replace your spark plugs if you haven't done so. Make sure there is no white build up on any of them too. I had a similar problem and replacing the sparks fixed it.
 
spark plugs are new my lower rpm sputter is fixed the stock maf I got was bad. tb hood, and injector seals good. still dying up top though??
 
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