I bought a 91 4runner, supposedly a rebuilt 3vze in it (some paperwork to prove) but hasnt run well since rebuild, almost 10 years ago. I have been researching relentlessly about what causes this and the fixes. So far i have replaced all related relays (efi, cor, etc), ive replaced all fuses in engine bay, and checked the fuses in the drivers kick panel, which were all good. I tried a different ecu, checked voltage to ecu and it was good. Ive replaced ignitor, dizzy, wires, checked voltage at coil, checked voltage going to dizzy, etc. Which were all fine. Recently found a thread on here about how the maf could be the issue, i popped mine open and it was fine. I have an extra that i know is good, tried it anyways, and it made no difference. None of which has made the fuel pump prime or run at all when the key is turned. When jumping the fuel pump, the vehicle starts right up, but runs poorly. Once revved up past 2k, the check engine light comes on and gives code 52.

My thoughts are the injectors aren't receiving correct voltage and causing the knock sensor to trip, but I still am at a loss as to why the fuel pump will not run unless jumped.

 

Because ... it's not supposed to. (So much for 10 years of relentless searching.) The fuel pump starts when the key is turned to STArt, and kept running when the VAF (not MAF - different technology) detects air flow. Here's everything I know about the VAF-COR circuit https://www.yotatech.com/forums/f116...-quits-312747/ , but I don't think that has anything to do with your issue.

Hmm. What a mystery. If only the CEL codes told you exactly what the problem is! And if the FSM told you that code 52 triggers massively retarded timing.

Your ECM is not receiving a signal from the Knock sensor. It doesn't means it's knocking, or not knocking, or anything to do with your injectors or bus voltage. It means the ECM doesn't know what the knock sensor is doing. The most likely cause is a problem with the "pigtail" from the knock sensor to a connector outside of the head. It's a shielded cable in a hellish environment. Alas, you have to remove the upper (plenum) and lower intake manifold to get to it. It's very unlikely to be the sensor itself (they're built like a brick), but for $100 (RockAuto) I think I'd replace it too.

But I won't lie; a lot of people have trouble finally eliminating that code.

Good luck.



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