nmchuck

I have a 1994 2wd 4Runner that loses power when it goes into closed loop after warming up. It runs good and has power when cold (well as much as can be expected from the 3.0) but once it warms up it struggles to get any speed at all. Is there a way to determine which sensor is triggering the timing to be retarded? There never is a check engine code stored, and I have swapped several sensor from my good running 1994 3.0 pickup without improvement. this includes the O2 sensor, VAFM, engine coolant temp sensor, TPS (new one installed and adjusted to FSM spec), even swapped the distributor.

I am wondering if the knock sensor is triggering the timing to retard, but no codes are present. I have checked timing, fuel pressure, replaced fuel filter and switched fuel pressure regulator too. I have searched this site and others extensively, but have not come across any real solutions. I am at wits end and could use the help from YT gurus!

nmchuck

Anyone have ideas? The symptoms remain. At times you can fell it surging during acceleration like it wants to clean up and run, but it never really does. I can shift to neutral, shut off motor and re-start and it will improve momentarily.

mholme

Have you verified with a timing light that there is a change in timing? Where is your timing currently set?

nmchuck

It is currently set at 12 degrees, good idea to check again to see if the jumper wire actually changes the timing. Will verify that tomorrow, was planning to try a different ecu I have access to just to see if that makes any difference as well.

Thanks for for your idea!

millball

Are you sure it's going into closed loop?? How do you know??

Only the most sophisticated scanners of that time can read Toyota OBD-1. Snap-On MT-2500 was one.

As asked above, does the timing light show ignition timing advance on reving the engine??

nmchuck

I believe it is because it starts running differently as soon as the engine is warm enough to allow the transmission to shift into overdrive. My logic is that the ECT sensor is telling the ECM that it is now warm and triggers the system into closed loop. It immediately starts to perform differently. The transmission shift points change (shifts earlier) and the engine is very sluggish. The timing is set at 12 degrees and does advance as engine revs up.

Since my last post I have tried a different ECM, switched out the VAFM and checked all vacuum lines again. I also checked the TPS again and set it to the specs in the FSM. Unfortunately these did not change anything on the performance of the truck.

Kind of running out of things to try, any ideas would be appreciated.

thook

you know it only goes into closed loop under certain performance conditions, right? i mean, it won't go into CL, of course, until the engine is at operating temp and the O2 sensor has heated. but, under acceleration/heavy loading it's in open loop. it's in closed loop just when cruising or idle. so, if it's losing power in all conditions at operating temp something else is going on.

i wonder if you're having egr valve issues...hmm