My 90 GS-X Falls on its face after 4000 RPMS

Ok I just bought a 1990 GS-X Galant and it has a real bad problem with acceleration under load. If the car is sitting out of gear in the driveway I can free rev it to red line no problem but once I start to drive it once I get around 3500-4000 rpms it starts to bog and if I floor it then it dies all together, it feels like the fuel is getting completely cut off. It starts fine every time, the idle is perfect but under load it really craps out. I;m new to the Mitsubishi world but I am very familiar with fuel injection. Is there something in the TPS that increases voltage to the fuel pump that could be off?

Any help would be greatly appreciated.

So far I have only replaced the plugs, valve cover gasket and I did a thourough check for bad vaccume lines.

Also I can really hear the fuel pump whine when its running, the tank and pump are out of a VR-4 so I don't know if there is enough voltage getting to the pump or what.

Hard to say. How are the plug wires? Does it misfire or completely cut out? Could try changing the fuel filter, coudl be clogged. If the pump is out of a VR4, is it stock or aftermarket? Could be a bad injector or just a clogged injector.

You are going to use a lot more fuel under load vs free reving at idle. If its not an issue with the plugs/wires, it has to be a fuel problem. You could try running injector cleaner through the gas tank(some people think it works, some people think it causes other issues). If your going to run the injector cleaner, do it before you replace the fuel filter as the injector cleaner will bring up the crud at the bottum of the tank.

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Originally Posted by seth98esT

Hard to say. How are the plug wires? Does it misfire or completely cut out? Could try changing the fuel filter, coudl be clogged. If the pump is out of a VR4, is it stock or aftermarket? Could be a bad injector or just a clogged injector.

You are going to use a lot more fuel under load vs free reving at idle. If its not an issue with the plugs/wires, it has to be a fuel problem. You could try running injector cleaner through the gas tank(some people think it works, some people think it causes other issues). If your going to run the injector cleaner, do it before you replace the fuel filter as the injector cleaner will bring up the crud at the bottum of the tank.

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It completely dies at WOT, the car still has power, lights and what not but the fuel is just cut off. If I feather the gas I can get the rpms higher than 4000 but its really strugling to get there.

I'll check the wires but I really think its a fuel issue

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Originally Posted by MaineGSX

It completely dies at WOT, the car still has power, lights and what not but the fuel is just cut off. If I feather the gas I can get the rpms higher than 4000 but its really strugling to get there.

I'll check the wires but I really think its a fuel issue

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Off topic, where are u in Maine, I go to UMO

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Originally Posted by MaineGSX

It completely dies at WOT, the car still has power, lights and what not but the fuel is just cut off. If I feather the gas I can get the rpms higher than 4000 but its really strugling to get there.

I'll check the wires but I really think its a fuel issue

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I agree. Its looking for a certain a/f ratio. If its not getting that it will idle like garbage or die all together like you said. At higher rpm's it needs more fuel. I can't give much advise at what to look for, but I would care to guess its the fuel pump or injectors. Your fuel filter would have to be really bad for it to cause it to die but its worth a look I suppose.

check your timing, and what everyone else said too.

I'm thinking its the fuel pump, I mean this thing is super loud. I checked voltage to it and its getting full BAT voltage but it whines like crazy. I also changed my fuel filter and it did nothing but it looked like the original so I was going to do it anyways. I live in Brownville wich is about 30 miles North of Orono.

What should the pump put out for fuel pressure?

And is there any bench test for the MAF?

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Originally Posted by MaineGSX

I'm thinking its the fuel pump, I mean this thing is super loud. I checked voltage to it and its getting full BAT voltage but it whines like crazy. I also changed my fuel filter and it did nothing but it looked like the original so I was going to do it anyways. I live in Brownville wich is about 30 miles North of Orono.

What should the pump put out for fuel pressure?

And is there any bench test for the MAF?

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I know stock 1g 4b63t fuel pressure should be 38psi with vacuum and 43psi without. Im sure its a bit higher with an NA motor?

interesting topic. im from manila, and this problem is not unusual with 4g63's. if you got your car 2nd hand, and you dont know the history, you might want to check the ecu. the 4g63 ecu has a notorious reputation for screwing up with age. while you can repair an ecu, some people just scour the junk shops for a replacement. we've seen this problem many times before, and sometimes, the wrong ecu was mounted. double check the ecu code just to be sure. is your fuel regulator still stock? grounds intact? pump okay? hope you solve your fuelling soon issue buddy.

Very good point. The majority of 1g ECUs were prone to leaking capacitors which damaged the board of the ECU. My 90 Talon had leaky capacitors and caused me not to be able to boost. In the winter it didnt screw up as much but once the car was warm the car would hesitate under boost. THe stock boost gauge would automatically start to fluctuate and the car would jerk really bad.

Depending on what part of the ECU gets corroded the issues will vary. Definitely something worth checking out.

I figured it out, I had a bad seal betveen the fuel pump outlet and the hard line thats inside the tank. The PO put a Walbro pump in the tank and it wasn't in right.