92 Pathy VG30E, tach jumping, timing irratic, running VERY poorly, HELP!

[danz]

Hello All! My name is Dan, and I need help!! heheh

I just want to say after doing some searching here the members are very helpful! So here is my situation, i prey you all can help...

My ride up the mountain is a 92 Pathfinder Auto w/ VG30E MPI.

The truck has been running with a lack of power for some time now... it also has a high idle sometimes. (an off and on will fix it sometimes)

A few days ago the driver tried to take the truck out of the parking lot of the bank and it died. started it back up, tried to move, it died again. The tach would be at 800rpm then JUMP right to 4,000rpm once the throttle is pressed.

It starts, (usually after the 2nd try cranking it) and it sounds like its running on 4 cyl's or the timing is off a tooth.

The truck limped back to the shop where we were able to put the MODIS/Snap-on box on it, which gave us a CAS error. we replaced the CAS in the dizzy, reset the codes, and still get the same error code, again! we tested the CAS with an alternative method which involves spinning it with the power connected and it checked out.

we attempted to see what the timing was at, and the timing marks would jump around. It was impossible to get a consistent reading off the crank. (this to me was very strange... seems like the ECU is trying to make adjustments and is being confused by something???) is there a way to disable the ECU from altering timing values?

we threw in some new bkr6ey's, replaced the rotor, cleaned the cap, still runs the same. i am convinced this is an ignition issue because of how the tach is acting. perhaps a faulty ECU? i sure hope not. i wonder how to test for this?

I am dying for ideas on how to get this thing running.

to do today:remove timing cover, ensure belt hasn't jumpedremove plug wires 1 at a time and check for change in operation


Modified by danz at 3:21 PM 1/8/2009

[MinisterofDOOM]

The only automatic timing adjustment the VG30E had was for knock prevention. No variable timing or anything high-tech.

to do today:remove timing cover, ensure belt hasn't jumpedremove plug wires 1 at a time and check for change in operation

Those would be my next steps. When was the belt last replaced? Those older belts had a very short 60,000 mile replacement interval. If it's a newer belt it may be good for 90 or 110k. It's possible there's been some stretching in the belt.

But your diagnosis of ignition system sounds more likely to me. Either not getting spark or not getting fuel. The plug-pulling test should tell us a lot.

[danz]

The only automatic timing adjustment the VG30E had was for knock prevention. No variable timing or anything high-tech.

But your diagnosis of ignition system sounds more likely to me. Either not getting spark or not getting fuel. The plug-pulling test should tell us a lot.

i was more referring to pure ignition timing control, like any ecu would do if it say high coolant temps, higher air flow, etc. good info none the less

update;we had a friend with a known working pathfinder come by. we swapped his ECU into the truck and it started GREAT, then died after 5 seconds or so. started it back up and it ran just like it did before. this is where it gets interesting.

we put the "bad" ecu in the "good" truck, and it ran fine. we then took the "bad" ecu and put it back into the "bad" truck, and it ran GREAT!! WTH?!

so now we have a truck that runs good, but could be completely unreliable. not your ideal mountain truck.

the only thing i can think might have caused this is a loose/poor connection somewhere in the ignition system, perhaps at the ECU. we are going to do the screw driver test and start tapping on things to see if we can re-produce the poor running conditions.

:

[danz]

truck made it up the mountain and back down with substantially more power. i credit this to new plugs.

but its running great, and all we did was put a different know working ECU into the truck, and put the stock ECU in a known good truck, then put the stock ecu back in the "questionable" truck.

all in all the inconstancy of it all makes me think its wiring related. we may never know.