92 pathfinder running rough

[Kensai]

A few weeks ago my '92 started running rough. When revving below 3500 or so rpm it's running like it has a vacuum leak, bogging down like you're in too high of gear when trying to accelerate. at this point it was idling under 500 and had no power when driving. I did a quick look through the vacuum hoses and found the large L shaped hose that runs from the main intake hose into the metal line that disappears under the intake plinth had a large crack in it. I replaced this hose and it helped but it is still stuttering when trying to accelerate and it just doesn't have the power it should.

So far, I have gone through every vacuum line I can find, and have found no other broken hoses but have replaced most of the small ones as well as the brake booster line. I have also done a spark test and it seems like all cylinders are firing alright. I checked the PCV valve and it was pretty dirty. My local parts store doesn't carry them so I cleaned the old valve (seems to move freely) and have a new one on order. I have cleaned the connectors on all the sensors I could find around the vacuum lines. I have tried unplugging the MAF, as well as the other two sensors that looked vacuum related (the one on top of the "tower" near the rear of the engine as well as the one on the little box that has 3 vacuum lines running to it under the throttle). The only one that seems to effect anything if you unplug it while the car is running is the MAF, so I'm not sure if the other two are working at all or not.

 

Today I checked my ECU mode 3 codes. It came back with 12 (MAF) and 34 (knock sensor). I cleaned my MAF and checked the wires again and that didn't change anything.

 

I'm not sure where to go from here. As if I wasn't stressed enough about this my registration came today with the dreaded EMISSIONS TEST REQUIRED stamp.

[Slartibartfast]

The knock code is probably because it's running funny. Not uncommon for it to crop up with other codes. As for the MAF, the grounds on them go bad sometimes. How's the connector look? You might try running an extra ground wire.

[Kensai]

I've checked the MAF and it's connectors a couple times. They seem to be working fine. If I unplug the MAF while idling the car dies.


Reading in the diagnostic guide pdf, it says that the knock sensor will make the computer retard the ignition. I have a pretty serious exhaust leak on the last port of the passenger side manifold, so I'm curious as to whether this might be causing the knock sensor and possible ignition retardation. Both studs are broken on that port so I plan to extract them and get that fixed up this weekend.

 

Does anyone know if there is a way to unplug the knock sensor without getting to the plug on the sensor itself? It would be nice to be able to test the car sans sensor without having to get to the actual sensor.

[Slartibartfast]

I've heard of knock sensors going off for things like loose heat shields but not for exhaust leaks. If the leak is bad enough, I guess it's possible that your oxygen sensor could be confused. If the leak got much worse at the same time that it lost power, this might make sense.

As for disconnecting the knock sensor without pulling the manifold, all I can think of is removing the relevant wire from the ECU plug. I remember someone talking about re-pinning that plug to use a different ECU so it should be possible to pop the connector out, then put it back, without cutting wires. I would also be very surprised if the knock sensor was retarding timing enough to make it idle that low.

Thinking about this I have two dumb suggestions. One is that the timing could be wrong (loose distributor moving around on its own or the timing belt jumped a tooth). The other is that the EGR valve could be stuck. You can check timing with a light (though it won't be the 15° you're looking for until it's warmed up) and see if the distributor will turn in the head by hand. For the EGR valve, it's got that diaphragm you can see from underneath. If you push that diaphragm up, it opens the EGR valve, which should at least drop the idle. If it doesn't change the idle, or you can't get it to move, it could be that your EGR valve is either stuck inside or getting vacuum when it shouldn't.

[Kensai]

I'll have a look at the EGR and check the distributor for looseness today when I'm fooling with the exhaust stuff. I have a loose heat shield on the passengers side because of few of its bolts are broken off. I've fooled with the EGR a bit, and adding vacuum kills the engine. Does that mean it's working properly?

 

 

 

Also off topic but I love your Triumph project car Slartibartfast. My first car was a Triumph Stag and most my mechanic experience comes from working on the MG I've had for the last 9 years and all my dad's old British cars.

[Dannyg]

I am having same issues. What was the problem? Was it the knock sensor?