br2an Posted September 9, 2004 Share Posted September 9, 2004 (edited) (note: I've posted this on another site but thought I would try here as well.) Just wondering if anyone has come across this before. 1993 SE v-6 Pathfinder, 105,000 km (60,000 miles) It has worked fine for quite some time but recently it would not rev past 2000 rpm. As soon as the engine reached this speed it would die, drop to around 1500 rpm then pick up again. Rev up to 2000 and die again. (same with load/no load) There is no missing, no hesitation, no backfires, nothing else out of the ordinary. It was like this the whole day until I unplugged the ecu (reset) and the problem seemed solved. Recently it began again but only for 1-2 minutes after startup and then is ok. This has happened a few of times (not consistently) over the past 2 days and lasts for a minute or two at most. I am thinking ecu (because reset solved it first time) but am wondering if this could be learned behavior by ecu from bad input? (say bad connections or sensors??) By the way, I did some arc welding on it recently (just before this problem) and I didn't disconnect the ecu. Again, has anyone else had a similar experience (rev limited to 2000 ) or weird problems after welding? (last confession: haven't checked for codes yet but will this weekend) Thanks for reading, Brian Edited January 21, 2007 by br2an Link to comment Share on other sites More sharing options...
94extreme Posted September 9, 2004 Share Posted September 9, 2004 i think i've seen this post somewhere.... anyway, definately run codes. there may not be any though. you didn't mention the check engine light being on. the welding could have had a negative impact. Link to comment Share on other sites More sharing options...
Reido Posted September 9, 2004 Share Posted September 9, 2004 I'd bet throttle position sensor. I've seen the same problem on a Toyota after a creek crossing. We had to bypass the sensor with a paper clip to limp home. Link to comment Share on other sites More sharing options...
br2an Posted September 9, 2004 Author Share Posted September 9, 2004 Check engine light doesn't come on. (still haven't checked for codes, this weekend I will have the time) Throttle position sensor problems are usually noticeable when you go past idle. I'm guessing your friends Toyota would start and idle ok but die as soon as he pressed on the gas pedal. Mine responds well to any part throttle or full throttle pressure. It just dies at exactly 2000 rpm. I am more worried that this is an intermittant problem (now seems like just after the occasional cold start, lasts for a minute or so and clears up). I find these types of problems are very difficult to diagnose. Thanks Brian Link to comment Share on other sites More sharing options...
k9sar Posted September 9, 2004 Share Posted September 9, 2004 check the connector on the top of your MAF. Next time it's running rough, pop the hood and give the wire and connector a good wiggle. That would definately cause a problem like you describe and it's much easier to find/fix than an ECU problem. If this does not work, I'm sure others will chime in with further suggestions. Link to comment Share on other sites More sharing options...
Reido Posted September 9, 2004 Share Posted September 9, 2004 Mine responds well to any part throttle or full throttle pressure. It just dies at exactly 2000 rpm. Right this is exactly what the Toyota did and it died at exactly 2000 just like you say. What happened is the TPS was stuck on sending an idle signal so no matter how much you move the throttle plate it is still telling the computer "we're in idle mode." The MAF sensor records more air flowing by so more fuel is injected which speeds up the engine to 2K. At this point the computer cuts off the injectors because that speed is too high for idling. After it drops to ~1500 it starts all over again. I'm not saying the TPS is bad for sure but it is the first thing I would look into. EDIT: Although the intermittentcy of your problem does complicate things. Link to comment Share on other sites More sharing options...
k9sar Posted September 9, 2004 Share Posted September 9, 2004 it's wonderful how all these things work together to cause a real pain in the a$$. Link to comment Share on other sites More sharing options...
br2an Posted September 10, 2004 Author Share Posted September 10, 2004 Reido Your explanation makes perfect sense. I had thought a bad TPS would not allow engine rpm above current idle, not the max idle. Now I think the intermittancy could simply be a bad/loose connection at the TPS. I believe this might even be weather related. I remember it was raining for a few days when I first noticed the problem. But today it was not raining and everything was ok. We are supposed to get a downpour tonight and tomorrow so I will see if it reoccurs. When I get time to look at it this weekend the TPS and MAF (suggestion from k9sar) connections are high on my list of suspects. Thanks again guys. Brian Link to comment Share on other sites More sharing options...
Guest SomePunkKid Posted September 10, 2004 Share Posted September 10, 2004 Mmm sounds like to me your troqe converter cluth is half way engaging Link to comment Share on other sites More sharing options...
Diesel Boy Posted September 10, 2004 Share Posted September 10, 2004 Ya what??? That theory really deserves to be explained!!!!!!! Link to comment Share on other sites More sharing options...
br2an Posted September 10, 2004 Author Share Posted September 10, 2004 Mmm sounds like to me your troqe converter cluth is half way engaging I'll save that as a very last resort (seeing as my vehicle is a 5-speed manual). Link to comment Share on other sites More sharing options...
Mr. Pickles Posted September 10, 2004 Share Posted September 10, 2004 I'll save that as a very last resort (seeing as my vehicle is a 5-speed manual). Be sure to check your blinker fluid while you're at it. Link to comment Share on other sites More sharing options...
87pathy Posted September 10, 2004 Share Posted September 10, 2004 Read my lips VACCUUM LEAK!!!! I could be wrong but that same thing happens with a motorcycle, old V8, lawmowers, etc. etc. etc. when you have a bad vacuum leak Link to comment Share on other sites More sharing options...
jmcardamone Posted September 10, 2004 Share Posted September 10, 2004 Here's my two cents... My 87 did the same thing, Only at 3,000 RPM. I checked the CAS and the TPS, both were ok. After Messing with it for about a week, the motor Blew... Right out the side of the Block! (thats why my 87 is listed in the "parts" section HA), anyhoo, If you havent Checked your Crank angle sensor or teh codes, Do so. if all seems well, Ensure that you have Sufficent Fuel Pressure and VOLUME! 88path Knows the Correct PSI, and the volume test one might mention on..... good luck! Link to comment Share on other sites More sharing options...
Guest SomePunkKid Posted September 11, 2004 Share Posted September 11, 2004 Geeze no need to get testy i did not know it was a 5 speed. Might wanna take a look at them muffler baerings tho. Link to comment Share on other sites More sharing options...
Diesel Boy Posted September 11, 2004 Share Posted September 11, 2004 LOL,LOL!!! True, and I suppose theres always a chance the oil on the fan motor is empty and its not turning the heads properly because the valving on the thermostat is preventing the air from circulating through the torque convertor leaving a lack of vacum in the anti detonation compression chamber. That would definatly be the cause for sure!!! Link to comment Share on other sites More sharing options...
kmgar99 Posted September 12, 2004 Share Posted September 12, 2004 Diesel Boy...that was great! i could'nt have explained it better myself (unless I was on drugs) Link to comment Share on other sites More sharing options...
Reido Posted September 12, 2004 Share Posted September 12, 2004 Link to comment Share on other sites More sharing options...
br2an Posted September 12, 2004 Author Share Posted September 12, 2004 Well, I finally checked the codes and it is a 55 (normal). I tried what was sugggested and here are the results. for reido and k9sar: I have checked the connections on the mass air flow (MAF) sensor and the throttle position sensor (TPS). Disconnected them, visually checked , sprayed with WD-40 and reconnected. Nothing seems out of the ordinary. (wriggled them as well) I even tried disconnecting the TPS and starting without it to see if I could get the symptoms to reoccur. It ran normal (unfortunately), easily revved up to 3-4000 rpm and didn't miss or anything. I didn't drive it like this but it seems the TPS on a pathy is not as crucial (for just getting home) as it is on a Toyota. 87pathy: No vaccuum leaks that I can find. And anytime I've had one in the past, it usually showed itself as a fluctuating or high idle and was hardly noticeable at high rpms. Never saw a vaccuum leak act as a rev limiter. jmcardamone: My oil pressure light goes out immediately after startup. I have no lifter noise (as you might hear with low oil pressure) and just today I had it pulling strong up to 5500 rpm in 3rd gear. As I mentioned earlier, when it occurs, it is like having a rev limiter on my engine. Anyone who has tried to see how fast a late model GM vehicle will go (at least here in Canada) knows what I am describing. My 99 Sierra would pull strong up to about 160 km/hr and then it was like somebody turned off the key. When it happens to the pathy it is exactly at 2000 rpm, whether it is in any gear, moving or not. This usually occurs after a cold start and then goes away in a minute or two. SomePunkKid: ?????? Conclusion: Right now the vehicle is working great (3 days in a row). If the problem reappears I will try a reset on the ECU and go from there. (I may even be forced to live with this little "gremlin" under the hood.) Thanks again everyone. Brian Link to comment Share on other sites More sharing options...
k9sar Posted September 15, 2004 Share Posted September 15, 2004 I like that solution. I was driving back from vacation yesterday and my check engine light came on. I checked the code and found that it was bitching about my O2 sensor. Simple fix... reset the ECU. No light, runs fine. Link to comment Share on other sites More sharing options...
Guest Pprince147 Posted December 7, 2004 Share Posted December 7, 2004 I know this is an old post and I posted my problem elsewhere. But this is exactly what my 93 se is doing. Except mine is doing it permanently and I can't drive it. I ran diagnostic, said 55. Then ran diagnostic according to the pinned page (very helpful) but found nothing. Checked conn on sensors they seemed fine. It starts up and idles beautifully. put my foot on gas and it revs to 2100 rpms and drops. Toy with accelerator and it will rev farther but then drop right back down once it notices it's over 2k. Mine did this intermittently at first (as yours was), but after I changed filters, cap, plugs, oil etc...it's done it permanently. I guess that's what I get for being nice to it. Anyways, did you ever figure any culprit out on this or just let it go? If you let it go, DO NOT DO ANY MAINTENANCE ON IT!! lol, this is when mine decided to do it all the time. Anyone? Anything? Link to comment Share on other sites More sharing options...
br2an Posted January 21, 2007 Author Share Posted January 21, 2007 Yes, this is an OLD thread but I have finally found the problem and fixed it. The problem (engine died at 2K rpm) came back and this time wouldn't go away on it's own! The fix: replaced throttle position sensor. Brian Link to comment Share on other sites More sharing options...
88pathoffroad Posted January 21, 2007 Share Posted January 21, 2007 The ECU will go into fail-safe mode if either the TPS or MAF are malfunctioning and not allow revs over 2800 RPM, to prevent detonation and/or engine damage due to running with the wrong A/F ratio. Link to comment Share on other sites More sharing options...
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