88 Trooper 2.3L engine, runs like a top from 3/4 full fuel tank, fill it full and it overfuels, black smokes, have to keep footfeet down to keep running when stopped. Drain 3 or 4 gallons out and runs good again. Even runs bad at severe angle.


You name it we have tried it, will hold constant 35-38psi fuel pressure, hit the gas and it will jump to 45psi. cold start fuel psi 45. Swapped fuel pump out of the tank, shortened the return tube, tested vacumn ports and routing, all sensors appear to be working,


I have a spare running trooper that we have swapped mass air flow, ecm, fuel pump from with no change, can't make the other run bad, can't make the one run good.


Any ideas, and no bull if you are the first to provide the fix, I will paypal you $50.

 

I would take your whole gas tank assembly fuel pump and all and swap it with your other one. Just a few bolts and hoses to hook up. If it changes anything you know the problem is in the tank, if not you know the problem is elsewhere.


Also did you check the fuel pressure when the tank is full compared to 3/4 full? Just curious.

 

already swapped complete fuel tank and pump, no change.


the fuel pressure is the same both ways, only difference in fuel pressure is at cold start up it will go as high as 45 psi then drop back to 38psi.

 

I believe the fuel regulator is vacuum operated, so it makes sense that the pressure is high until the engine generates some vacuum after starting. A great source for advice and parts is Jerry, who is around these forums once in a while. You can email him at Jlemond@bellsouth.net.I don'tthink he will mind. He is an Isuzu genius and sells his parts at his cost. I have bought my OEM parts from him many times, from brakes to engine parts. The best part is he has a proven track record. Hope this helps. Good luck.

 

thanks I will send him an e, I have had this trooper at a shop for several weeks and they have put quite a few miles on it and finally told me to take it home, they could not figure it out.

 

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Have you looked at the evap system sucking fuel through the carbon canister? when full could have enough vaccum to suck fuel that way
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yep, checked that, even when the tank is down almost to 3/4 you can get on a downward angle and it will start running bad. Air blows freely through the vent lines on the return as well.


I have even ran it with the fuel cap off and it still will bearly run, when it dies it is a b----h to get it started, only way to keep it running is keep giving it lots of throttle.
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try to disengage the fuel pump with pulling the fuse and see if it will run without the fuel pump running.
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check the canister and see if fuel is in it
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will give this a try, the fuel pressure is running within specs so far, and no fuel in the canister...