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Betcha Can't Answer This Problem!

I have a 93 infiniti J30 and when I start it up in the morning it runs fine for about 10 to 20 minutes, when the engine gets heated up.

Once the car is warmed up however, it won’t rev past 3000 rpm in any gear, and has no power. It misses and surges, the rpms jumping from 2200 to 2600 to 2400 to 2800 and so on even when the gas pedal is pushed to the floor. It idles just fine though, and it runs ok when i press pedal lightly (around 1500 to 2000 rpm) but messes up as soon as it hits 2000 rpm.

I have checked to see if the catalytic converters were backed up, replaced the mass air flow sensor and ignition control module, and none of this was the problem.

There is no check engine light on, even when I unplug some of the sensors. I know that the ECU is only OBD1, but shouldn’t the check engine light still come on anyway?

Right now I have some theories as to what the problem could be. The fuel pump? but why would it start acting up after the cars been running for 10 to 20 minutes? Wouldn’t that cause the problem immediately?

Another theory is the engine is overcharging the battery, which in turn could be affecting the way the sesors read. I have no voltage meter so i can’t test it.

My last theory (and the one i’m leaning most towards) is that the Crank Angle Sensor is going bad, giving the ECU a bad read.

Well this is all I can think of, if you think of anything better, then reply to this post. But I betcha can’t answer this question.

I took off my Crank angle sensor, and the shaft that turns with the engine binds and catches making it hard to turn. I think that it is my problem, though I really wish I could test the fuel pressure somehow too. Please provide any input you have to offer, as it is much appreciated.

You win, I can’t answer your question/

haha. Neither can I. And its my problem.

Not sure -but it might be similar to a problem I had a few years ago. My cars different, but I think it may be the same engine family as yours…'96 Nissan Pathfinder with a VG series motor (V-6, mine’s a VG33E). Below is the sequence of events over a period of about six months…call the incidences “idle spurts”…

I’m waiting at a stop light, engine is idling regular, and then it jumps up and down between under 1000, up to 1500 rpm. It did this once.

Months pass, and then it does it again, aslo while waiting for a light to turn green.

A few weeks later, it does it again, although it was doing it more often for about the next month. Most of the time it was while waiting at a stoplight, but a couple of times it would do it when I’m slowing down (foot of the gas), and ALMOST stopped - but when it would happen under that circumstance, I’d be coasting down while the transmission is in drive, so the “idle spurt” would actually cause the car to accelerate just enough for me to realize I’d better apply the brakes a little harder so I can stop where I need to.

The “idle spurt” is also the cause of how I cracked the tip of my mirror housing on ther edge of the garage door frame opening…as I was backing out the idle decided to spurt and accelerate the car right when my mirror was really close to the garage frame.

The end of the problem came when finally one day the car stalled driving home from work about a week later. Finally the check in light came on (after all of this time)! I was able to restart the car, but I had to feather the throttle very lightly and drive like a grandma permanently asleep, othwise it would stall. If I grandma’d the throttle it would drive fine.

…Turns out the throttle position sensor was either out of adjustment, or just plain bad. The part cost $90, and the Haynes manual has a two hour procedure, but I also found a 15 minute procedure on ALLDATA’s website (in a Nissan Technical Service Bulletin) which involves using a conductivity tester and is really easy. I had a hunch it was the TPS, but general driveability was fine, so I didn’t bother with it until it REALLY needed to be replaced. The check engine light revealed several trouble codes (maybe 6 or 7), but it did list the TPS as one of them so I replaced that only, cleared the codes, and that was all it was.

Sorry for the long story, but I hope it gives you a sense of if your car’s behavior is similar, or totally different.

My guess…it needs a new Throttle Position Sensor, but get the car’s computer scanned first to confirm it.

The TPS on my car costs 25 dollars and I’m working on very limited funds. I don’t think it is my TPS because I warmed up my car and then took my tps off and stuck it in the fridge and put it back on but that didn’t fix it. The problem is heat sensitive so i think i can rule that out. also when i unplug it the engine dies, which gives me a hint that it is working properly, although I did unplug it and started the car and the symptoms are the same. Maybe it is. I’m going to replace it anyway.

Why not just test the TPS - you can do it hot & cold. You can get a cheap meter for $10 or so (though spending $20 or more is smarter). It sounds like that might save you $$ in the long run.

Either back probe the TPS or make up some jumper wires. W/ the ignition on it should read near zero volts (specs vary, maybe as high as .5V) and the voltage should increase very smoothly as you open the throttle plate - ending up at about 4.5-5V at WOT.

Do it cold and observe. Then do it again hot & observe. If its getting wacky when hot you should see it.

Ok. But now the car doesn’t start. At all. It just cranks over and over. and since I have started the car without the TPS connected, I know that that can’t cause the car not to run. Which leads me to suspect once again the Crank Angle Sensor. I do know for a fact that if that is bad it would cause the car not to start. I think i will replace both, although it won’t be until the tenth, but I will let you know how it goes. Any other suggestions will be welcomed until then.

I have heard of crank sensors and cam sensors causing those same problems. Have a friend who’s car would run fine until i warmed up too. Turned out the cam sensor was bad. I would suggest checking for trouble codes. There should be some in there, even without the bummy light on, with as many sensors as you have unplugged. Try clearing the codes then running the car again and recheck for codes.

How do I check codes? or clear them?

spark plugs and wires are fairly new?

Yes, But this care has direct ignition which means no wires. And if it were the spark plugs or coils, I would know as soon as I started the car. The coils work fine, I have tested them. But now the car doesn’t start. Thanks for the suggestion though.

Since it won’t start you need to determine what’s missing; fuel or spark. Keep in mind they’re related but we have to have a starting point here.

Spray some aerosol car cleaner into the intake tract and see if the engine will run for a few seconds. It it does that means it’s a fuel issue but a fuel, or lack of, problem could be due to something in the ignition system, etc. Federal law is behind this.

A failing fuel pump can get a case of the stupids and act just like this so don’t rule that out.

Well i get fuel, because it started yesterday. Today I took off the fuel line and cranked her over and saw fuel jet out of the hose. I need a fuel pressure tester but the car won’t make it to any shop. I get spark too, whick indicates a timing issue… which again leads to the CAS.

Also keep in mind when a car’s computer runs in open loop and closed loop:

Open Loop:

  • After resetting the computer (clearing codes, replacing a battery, after a dead battery period)
  • During each start and initial warm up cycle

Closed Loop:

  • After full warm up period
  • If the computer was reset (per above), it takes several miles of driving around for it to “learn the system” and switch to closed loop operation

What I’m getting at is you could have the situation where your car runs fine in open loop where it only uses factory programmed sensor information mapping, and then after it’s warmed up and switches to closed loop, your vehicle goes awry because one of the sensors is malfunctioning. I second "albertk77’s suggestion above in using a code scanner to check for trouble codes, even if your dash doesn’t display a check engine light…that light only comes on for issues the factory programmed it to come on for, which isn’t all of them.

Yes but what could have caused my car to stop starting now? and is there anyway to read the codes without the scanner?

Earlier you mentioned you took the TPS off to cool it in the fridge, and then put it back on. Even if the sensor was good and just a little out of adjustment, now it may be really out of adjustment causing it not to run at all. At this point the thing to do is find the TPS adjustment procedure for your car and get it set right (since you took it off at one point)…when that it set and you still can’t get the car started, then you may be looking at something else (unless the TPS really is bad).

As far as checking the codes without the scanner goes - the Haynes Manual for your car may have some sequence description which involves the number of times you switch the ignition on, or a button you press on the computer when the ignition is on.

I know you said you didn’t want to start spending money on new sensors, so I’m sure you don’t want to buy a scanner…trust me in that if you get a GOOD one, it’s worth it!!! Don’t think of the scanner cost as an additional cost for this repair, think of it as a tool you will use on any car you maintain for the next decade or more. I bought the AutoXray EZ Scan 4000 about seven years ago…at that time it was almost $400 (now under $200), and even at that aweful price, I don’t reget it for the usefulness of it.

ok reset TPS and tried to start it. No go. Unplugged it… No go. It started unplugged before. Hmmm… I’l shop around for scanners. They seem to be a really good investment.

Debris in your fuel tank takes about 10 minutes to collect around the fuel pick-up sock (in-tank filter) and plug it up. When you shut it off for a while some of this debris drifts away, allowing a re-start. The process keeps repeating…

Check for fuel flow and pressure when the problem is present…

will do. I’m going to buy a fuel pressure guage. They aren’t that expensive. Does anyone know what the fuel pressure is supposed to be at idle for this car?