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Bad hesitation issue, I still cant figure it out

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Novablue454

15+ Year Contributor
166
0
Oct 21, 2006
Arvada, Colorado
So I figured i'd post in the problem diagnosis thread. So if you dont know, heres the deal. My talon is having some issues with hesitation upon acceleration. Its a 90 turbo AWD. The mods are a Hallman MBC, an Apex'i SAFC II, an Apex'i N1 catback, a TurboXs RFL BOV (recirculated), a Walbro 255, and an Aeromotive FPR.

Upon acceleration between 2500 and 4500 rpm, I can hear the car start to studder and feel it stop pulling as hard. It does it more often at part trottle, but occasionaly under full. If anyone is familar with vaporlock, it feels almost like that.

The problems started right after I got my car back from 9 second racing. I installed the fuel pump, the BOV, and the exhaust myself, but had some issues with the SAFC. On the way to the shop it drove fine, it was just idling at 2000rpm (i assumed because of injector overrun, as this was before the FPR). They finished installing the SAFC, and put on the MBC. It ran fine for a few days, untill one day I did a full throttle 1st-2nd-3rd-4th pull, and then it just lost all power and could barely drive home. I got it home, and replaced all the plugs with NGKBPR6ES. I performed a boost leak test, and found that the injector insulaters were leaking, as was the BISS o-ring (i believe) and the little plastic piece under the thermostat housing. I replaced the injector seals with the Home Depot ones, and I did a smalled version of the vacumn line elimination consisting off all the lines off the throttle body.

The MBC is set all the way down at 10psi, but at the time that everything went haywire it was at 16psi. Now if I try to turn up the boost any, it just studders worse and still wont go past 10psi.

The car is running alot better now, but its still studdering quite a bit. Im starting to lean towards the SAFC, as the engine RPMs that it reads are around 3700, when the car is at redline.

Does anyone have any other ideas or suggestions?
Thanks in advance.
 
ive only had the car about two months, so ive never changed it. Nor do I know if its ever been changed.
 
Novablue -
A Pocketlogger ($125 for the software & cable and about $30 for a cheap PDA) is the best investment you can make if you plan on doing your own troubleshooting, tuning, and wrenching on your own car.
How did you dial in your SAFC without knowing what your fuel trims were doing?

Go to pocketlogger.com or the classifieds for the software & cable. Ebay is good for a cheap PDA.
 
ok i got a Palm m100 off ebay and a cable and software from obdloggers.com It was $60 total. It wont be here for a while though. And I havent tuned the safc. its just installed. What does the sensor located on top of the air canister do?
 
oh. its the boost control solenoid. I know that. but does disconnecting the vacumn lines mess anything up?
 
If i'm reading it correctly it was running fine even after you got the car back from the shop,from reading your first post, you said it was driving fine up untill u did some full boost runs,so the only variable that changed was a few pulls at full boost.I wouldn't go changing your afc settings just yet as that was not the problem before hand.Common problems with full boost runs are couplings,hoses popping off,bursting seals, and gaskets.
 
The rpm problem wouldn't be caused by the SAFC since it just reads the signal. For now, you don't need to tune the SAFC, since you aren't running larger injectors. I would verify all your settings on the SAFC, just in case. It "should" store the settings, but you never know.

Being that you have a 1g, I would pull the ECU and crack it open. Look for anything burnt or a funny smell. Next thing is to check your knock sensor, which is a common problem on 1g's. Check it for "goo leakage" and make sure it isn't overtightened. It could be that the power loss you are experiencing at WOT is a result of the ECU jacking your timing.

We can diagnose this problem more efficiently when you get your logger, but that will give you something to do until it arrives. :thumb:
 
well i set the safc to a 2 cylinder car and now it runs perfect at stock boos with no MBC, but when i try to increse the boost and install the MBC, it studders out at 10psi.
 
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