Major misfire

[MettlerJa]

My apologies if this topic has been covered, I did try to search the old posts. I am a new Quest owner (wanted one for years) and I just recently bought a 98 with a disclosed issue, knowing I would need to make repairs. So, here it is:
*Red hot catalytic converter
*When cold, starts and idles fine
*Soon after, starts misfiring/sputtering
*When at running temp, misfires really bad
*New distributor cap, new rotor, new fuel filter
*167,000 miles
*Every few seconds, the speedometer drops in and out

When I bought it, the owner showed me paperwork from their local mechanic who stated that the front cat needed to be replaced in order to solve this problem. So, I did. No change. I checked a couple spark plugs, and they could stand to be replaced, but certainly did not appear to be completely wasted. I have more than several ideas (ignition coil, fuel pump, MAF, EGR valve, back pressure hose - BTP, timing is off, etc..) but, I have a feeling there is a common issue here. If anyone has any insight, I would love to hear from you. Much thanks in advance, it is greatly appreciated!

[MettlerJa]

UPDATE: I finally got a CEL on today. Scanned the code and got a P0325 - Knock sensor. Also, about 2 hours ago, I took it out for another test drive after fixing the vacuum line between the EGR and modulator. It died about 5 minutes into it. Once I got it started again, still misfiring like crazy, I got on the throttle a little more trying to make it at least get uphill, and WHAM! All of a sudden it started driving and running like it was new again, out of nowhere. 30 minutes later, back to the misfiring again. So, another question: Could my knock sensor be the problem, and just happen to want to work again for a few minutes, or is this something that should not have happened, because once that sensor is dead, it's dead? If so, I would just go get the sensor. However, if that IS the situation, I would think there is more of a connectivity problem here, than the sensor itself. Although there are no responses to this yet, I would still love to hear what anyone else has to say, before I remove both manifolds to get to the sensor.

[ricebike]

i have the same gen quest, but my misfire problem isn't that bad ...yet

yeap, i get the ocaasionally knock sensor code too, but it doesn't trigger my CEL at all.

did you remove the cap/rotor and inspect the distributor as well? i read about oil going up that shaft and other problems.

when your vehicle reaches operating temps, it changes to" closed loop mode" and some input sensor is throwing your engine in a funk. maybe replacing the knock sensor may or may not help. clear the codes and see if it comes back.

The P0325 code means that the Knock Sensor is not working properly. Problems with the knock sensor will not cause an engine performance problems.

Possible causes
- Faulty knock sensor
- Knock sensor circuit poor electrical connection
- Knock sensor harness is open or shorted
- Faulty Engine Control Module (ECM)


Read more: http://engine-codes.com/p0325_nissan.html#ixzz3n2eRIDHP

mind his accent, just for illustrative purposes on how to get to that sensor; he corrected himself to get the unit with the OEM plug already wired to it to avoid any issues in the future, so don't get the pigtail-cut/your/own type

you can fool the system by disconnecting the o2 sensors, thus forcing the system to run "open loop mode" but that's at a cost of lower fuel mileage, because you're forcing the system to run off the factory program in the ECU. CEL will stay lit, but you can rule out that the injectors/plugs/wiring/rotor/cap are working OK

red cat can also mean one of your injectors are leaking too much fuel?

another thing; when was the last timing belt change? i know for a fact that we have non-interference engines due to the yahoo members providing hard evidence that the heads were modified via the joint-venture with ford/mercury so we won't have catastrophic failure when the belt snaps. did the previous owner did the whole set, including the tensioners?

as for the speedometer dropping in/out, it may be a VSS that's mounted to the trans that went out for me. either that or the wiring to that sensor is going. I removed the sensor first to do a visual/electrical test on mine & found out my sensor is seized i guess from lack of lube to the spinning bearing or something... <shrugs>

[ricebike]

to add looks like others are replacing the sub harness too?!? and they confirmed that having a knock sensor code wouldn't turn on your CEL or cause misfiring issues... good luck & keep us updated so we can learn from each other

http://x.nissanhelp.com/forums/quest/14 ... p0325.html

scroll to page 2 and the OP found out that it was an open wire to one of his o2 sensors that was causing his misfiring problem, eventhough it didn't set a code for the o2 sensor

[MettlerJa]

I'm actually going to disconnect the 02 sensors this afternoon and see what happens in an open loop. I'm doing this before blowing out the EGR valve and cleaning the fuel injectors. The distributor is in great shape and really clean. I've been slowly doing things one by one, easiest first, simply because I get about one hour a day to work on it. I will let everyone know what happens from here .... thank you!

[MettlerJa]

No difference was made when I disconnected the 02 sensors. So, I am onto the EGR valve and fuel injectors next.

[ricebike]

Yup, u have to chase a mechanical condition, since I was reading your original post saying it was fine when cold/ running in open loop mode. How worn are the platinum plugs? And did the previous owner changed that timing belt/water pump?

Vss is the easier fix... Maybe check for intake manifold leak as well??

My bad about that knock sensor bid/ he was relocating it , but its weird that most forums says the knock sensor shouldn't have turn on the CEL... It doesn't on mine...

[MettlerJa]

*Plugs are new
*I would not know when the timing belt was changed, that information was not available
*VSS is now brand new
Next, I am going to clean the EGR valve. I need to research more on testing the intake manifold, but plan on that as well.

[emespenn]

Okay, here it is 6 months later.... What happened? What was it? Am I the only one who is experiencing these very same problems? I'm running out of resources. Can anyone help? Please?