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Possible limp mode, crank position sensor


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I somehow have been roped into driving my buddies 93 vg30 manual from portland to colorado, but first it needs to instill some faith in me that it'll make it that far. From a cold start, it drives and pulls like a champ for around 15 minutes, when it then feels like it goes into limp mode. Won't rev past 2500-3k, and surges and sputters hard once it's in that range. Only code is for a knock sensor, but in the maf/crankshaft/ignition check, the ecu says that the crankshaft position sensor needs looked at.

 

All this feels like a maf to me, but the (aftermarket) thing looks brand new inside and out. Pulled and cleaned it, as well as checking continuity from the plug harness to the ecu, without issue. The plug also has good power and ground, and the signal wire isn't giving me crazy voltage when revved. And yes, the plug and pins are tight/straight. 

Replaced fuel filter and ran some injector cleaner though with some small results, but nothing really fixed.

 

Where is the ckps located on these rigs? I keep seeing differing info on between the interwebs and fsm that it's part of the dizzy. Little unsure why it the ecu doesn't give me an outright code 11, but does in the deeper menu.

 

What else should I check? I'm not a nissan guy, but from my couple days of banging my head I'm seeing that the knock sensor isn't really worth the trouble, nor would it throw the truck into limp mode. Until then, I'll keep working away at these front cv axles.

 

Thanks in advanced

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I had a 88 V6 and mine was located inside the distributor at the very bottom of it. It's about the size of your palm and it's black plastic with one plug and what looks like a small mini CD that spins. Very easy to replace. I'm not sure if that will be the same on the 93 but if the part is the same for diff year models that will tell u. Btw I replaced mine and I was wrong it needed a timing belt. Those have to be replaced every 60k. If it skips or jumps your done. Interference engine keeps turning and will bend a valve or worse

Sent from my moto g(7) optimo maxx(XT1955DL) using Tapatalk

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Yep, the cam and crank sensors are combined and mounted under a dust cover in the distributor. It is an optical unit that uses a rotor plate that has 6 slots with one larger one for the crank sense and 360 tiny ones on the edge of the rotor for the cam sensor. Generally it is about $20 more for a complete distributor than just the sensor assembly. 

 

Seems like it is working fine until it goes into closed loop. It is possible the problem is a failing O2 sensor that is reading wrong. I don't recall exactly which mode you can put the ECU into to monitor the O2 sensor switching, but that info is easily found.

Another possibility is a bad engine coolant temperature sensor. If it is giving incorrect readings, the engine will not be happy. 

Try checking the spark strength when engine is cold vs warmed up. If the coil is breaking down or the distributor is starting to fail, you might be getting a weaker spark when everything is warmed up. 

 

Those are the best I have off the top of my head when I am supposed to be asleep. 

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Thanks for the leads everybody. After a couple days replacing most of the front end suspension, I'm back looking at this issue. The engine coolant temp is interesting, the needle doesn't raise much past the halfway point between cold and vertical. I'll look more into that one. I'll run the o2 sensor tests as well.

Running though the flow chart for the crankshaft position sensor, I'm not seeing battery voltage (only ~55mV) at the harness plug when the key is on, but there is continuity from the plug to the ECCS relay. The fsm says to check F52-M94 plug, but I can't find that one either. The fact that it's getting some voltage, but not full voltage is strange to me. 

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For any unfortunate soul reading this in the future, for me my issue was solved by simply cleaning the crankshaft sensor in the distributor. I ended up replacing (in total,) the fuel filter, water coolant temp sensor, and all 6 plugs before digging into the dizzy. But after a broken rotor, bolt, and compressed air, it runs like a top. 

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Good to know. However, was the dust red or grey in there? That part of the distributor is supposed to be sealed and grey or red "dust" is usually an indicator that the shaft bearings are starting to fail. A problem I have seen several times in R50 distributors, though I haven't seen it in WD21's that I can recall. 

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On 8/17/2020 at 10:53 PM, Mr_Reverse said:

Good to know. However, was the dust red or grey in there? That part of the distributor is supposed to be sealed and grey or red "dust" is usually an indicator that the shaft bearings are starting to fail. A problem I have seen several times in R50 distributors, though I haven't seen it in WD21's that I can recall. 

I've seen it in many Xterras (also vg33) but never a wd21. They must have changed bearing suppliers for the newer ones.

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Since it only happens once warm, I'd look in to the O2 sensor or the coolant temp sensor.  There is a test mode on the ECM for O2 sensor response.  You can find a description online somewhere but the jist is once in the mode the two LED's should blink together, and do it rather rapidly.  faster than you can click a bic pen. If it's slower than you can click, or the LEDs are not in sync, replace the O2 sensor.

 

have you inspected the wiring for the knock sensor?  Not usually something to cause a symptom like you're describing and OBD1 can be aggravatingly fuzzy when setting a code. It'll set the knock sensor but it'll be because the air flow sensor isn't reading right and causing the mixture to be off or some such BS.

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