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Mystery P0171 & P0174

Old 04-16-2015, 06:10 PM
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Join Date: Apr 2015
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Default Mystery P0171 & P0174

I bought a 1998 Rodeo, 4x4 V6 3.2L. While test driving the car I heard a rod knock. The dealer had a mechanic put in a salvaged engine. It runs great, but, shortly after I bought it, the check engine light came on.

It started with a P0101. I replaced the MAF sensor.

Then came the P0171.

I replaced the bank 1 HO2S (pre-cat). I've also replaced: IAT sensor, and the fuel pressure regulator. It's the 3-98 model so the regulator is a PR283.

Now I am getting P0171 and P174.

The HO2Ss are toggling. I tested for intake leaks by spraying air flow sensor cleaner all over the intake system while monitoring the toggling of the HO2Ss. No change was detected. I deliberately opened the intake system a little and sprayed some on the leak I created and saw the change right away.

I did a fuel pressure test where I jumped the pump relay with the engine off. It came up to 42 PSI immediately. With a hand vacuum pump, I can make it drop to about 32PSI.

The 4-98 has a PR223 regulator.

I'm wondering if the mechanic used the fuel rail from the one engine and the injectors from the other. The codes are consistent with low fuel pressure, and the PR283 (mine) is rated 44 PSI (according to the guy at JC Whitney) and the PR223 is rated 47PSI.

The scan tool said that the long term fuel trim is 23%, according to the factory manual, +/- 20% is within spec.

I'm considering getting the other style fuel rail from a salvage yard and trying that. I am of course interested in any other insights I can find before I spend any more money.

Incidentally, when I pinch the fuel return line, the pressure jumps to over 60PSI. I have not yet tried measuring flow, but, I'm going to do that next.

Thank you for any help that's out there. Other than this problem, it's really a cool car.
Old 04-20-2015, 10:29 AM
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Join Date: Apr 2015
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To clarify one thing, I have no idea what model car the salvaged engine came from. I don't know what parts were mixed/matched with it either. The check engine light came on the first time I was driving the car AFTER I signed the dealer paperwork.

OTOH, it runs fine, I just want to make the CEL go out.

I found a fuel rail from a 2001 and installed it over the weekend. The new rail uses the allegedly higher setpoint FPR. Well, it's still at the same pressure as before. Engine off, pump running, it hits a little over 40PSI.

I put the return line into a gas can and at the regulated pressure, it pumped about 1/2 gallon in a minute. I don't think it's the pump.

I bought the rail complete with injectors, but, I didn't change the injectors, I used the rail with my existing injectors, so, I can still try that.

I was wondering, is there's a way to find some higher flow injectors? The computer thinks the pulses it's outputting are too long. With a little more flow, that would change.
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