Well I was called in to look at a friends truck I believe it is early 90's. Anyways they problem is it has hardly any power until 3000 rpm then it seems to pick up a little bit. So far he has replaced O2 sensor, MAF, adjusted TPS, new coil, new fuel filter, and plugs. He has just been throwing parts at it and to me it seems like it is something electronic. But I am wondering what could be left.

When it idles it sounds like it has an exhaust leak at the manifold but it doesn't. I can make it run better by manipulating the MAF manually when it is unhooked from the intake tube.

Any ideas? He hasn't touched anything mechanical so I don't think there is a problem there. He said it just happened when he was driving home and it was an instant loss of power and flooring it has no result it is very hesitant.

Thanks,
John

 

have you replaced any of the plug wires? I replaced the wire from the coil to the distributor and that made a world of difference... its just a though.

Is there a check engine light?

 

Wires have been replaced as well. No light or codes. It's being a pain to say the least.

 

Have you checked compression? Start there, and also check ignition timing. Pull the distributor cap and see if it's wet.

If all of those check out to be good, I would pull the valve cover and check the tension on the timing chain. If the cam chain guide broke, or the tensioner failed, your cam timing will be off, which would of course make it run poorly. If you get the valve cover pulled, and everything else is good, start checking valve clearance.

Good luck!

 

Thanks forgot to add he put a new distributor cap on as well. Compression is even across the board. Guess I better check the timing and pull the valve cover and see if the chain jumped a tooth.

 

Check that ignition timing first, then, if necessary, pull the valve cover.

 

I will check the timing first.

 

So timing checks out fine. So is it possible the igniter is at fault?

 

clogged EFI?

 

I don't think so because 3000rpm and up it revs faster and is not so hesitant.

 

ohh.. well it couldnt hurt to run a bottle of injector cleaner through it

 

ummm did you take a loook at the throttle sensor?

 

looks like this

 

Since most of the sensors and electrical components have been replaced, they *should* all be good. Did he replace / check the temp. sensor?

You said the compression was even across the cylinders, what was the actual PSI? Was that when the motor is hot? If the compression is really good when the motor is hot, then it shouldn't be cam timing like I mentioned before, or a tight valve. Might not be worth it to pull the valve cover to check.

I would be going back through and checking the resistance of every component the FSM gives specs for.

 

Tested the igniter last night and found that the voltage in the final test was below spec. Spec is 5-8 volts and we were getting just under 3. I believe the compression was at 145psi and not sure on the temp of the engine. I told him to do a dry and wet test to check to see if there was some ring issues but it all checked out. So I guess we will try the igniter next. As the spark looked a little on the weak side when initially tested.

TPS was adjusted and inspected as one of the first causes.

Haven't done the temp sensor does that affect running at all engine temps because we got the engine to normal operating temp and still running poorly.

 

The temp sensor is what tells the ECU if the motor is warmed up or not. There's another thread on here where the guy had one that was way out of whack. It's not resolved yet, as far as I know, so I'm not sure if that took care of his problem. I've been meaning to try and find out, so I'll let you know.

If you wanted to rule it out, it's just a simple resistance check on the sensor. Looks like you may have found something with the ignitor. Good luck and keep us posted.