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Topic: Iac (Read 4202 times) previous topic - next topic

Re: Iac

Reply #15 –
The only way the ISC could cause surging would be if the plunger is moving in and out while at idle.

Try disconnecting and pluging the vacuum line to the EGR valve.
See if that makes a difference in how it runs.

Re: Iac

Reply #16 –
Lets start over.......

Have you checked your fuel pressure..

New ideas here, Fresh thoughts!!
One 88

Re: Iac

Reply #17 –
I am almost certain it is something to do with the ignition. But, I will check the fuel pressure. This is what the car does:

1.) Start car, car idles normal and everything seems ok

2.) Put car in gear, at first it acts normal and engine does not hesitate

3.) Driving, suddenly tack will jump around from about 1k up to 4k, this happens during acceleration, cruising, idling, it doesn't seem to matter. It seems like it occurs at random times. During the ignition surging the car hesitates/misfires.

4.) About a minute passes, the tack will go back to normal and the engine will stop hesitating/missing.

This happens at what seems random times. I drive 120 miles everyday, sometimes the engine will only do this once or twice, other times it will do it most of the 120 miles.

Re: Iac

Reply #18 –
Quote
I am almost certain it is something to do with the ignition.
Seems like it to me too. Since the tach's reading is based on how many/how often ignition pulses are being sent to the coil, it sounds like there's a whole bunch of signals arriving when they shouldn't be.

Have you checked inside the distributor to make sure there's nothing bouncing around in there that interfere with the Hall Effect Sensor or its parts? I remember seeing a Tech "stumper" in the back of an auto magazine where they found the roundy-round part had actually separated from the shaft. Maybe yours just has something messing with the windows, or stuck between the sensor and magnet.
Death awaits you all with nasty, big, pointy teeth.

1988 5.0 Bird, mostly stock, partly not, now gone to T-Bird heaven.
1990 Volvo 740GL. 114 tire-shredding horsies, baby!

Re: Iac

Reply #19 –
Like MasterBlaster says the Tach is driven by ignition pulses.
The problem is probably where he says it is. Something quick you could try to eliminate the EEC as a suspect is drive with the SPOUT disconnected for awhile.

Re: Iac

Reply #20 –
Dumb question, what is the SPOUT, and where is it? When I took the distributor cap off I didn't find anything but I did notice these scratches in the plastic of the cap. I don't know if that is normal or not.

Re: Iac

Reply #21 –
Looks like someone either spun the engine when the cap wasn't screwed down, or had no idea which way it was supposed to go on and kept twisting it back and forth until it finally popped on, scratching the insides with the rotor tip.
Death awaits you all with nasty, big, pointy teeth.

1988 5.0 Bird, mostly stock, partly not, now gone to T-Bird heaven.
1990 Volvo 740GL. 114 tire-shredding horsies, baby!

Re: Iac

Reply #22 –
Spark out (SPOUT) is the wire from the EEC that tells the Thick Film Ignition (TFI) module when to pulse the ignition coil.
The TFI is mounted on the distributor. Look at the cable plugged into the TFI. One of the wires has a connector that allows you to disconnect that one wire. That is the SPOUT.
This allows the TFI to pulse the coil without control from the EEC.
Your ignition timing will stay at the "base" timing of 10 degrees BTDC.

Re: Iac

Reply #23 –
So if I unplug this wire, and the car stops the ignition surging/hesitating the computer is bad?
 

Re: Iac

Reply #24 –
It means the computer may be bad.
It takes some very sophisticated and expensive tools to pin something like this down 100 per cent for sure. Especially without a process of elimination to eliminate some of the suspects.

So the best we can do is give you some insite in how it works and
suggest what is most likely the problem.

I will say that if it still surges with the SPOUT disconnected and this is really an ignition problem, it is not the computer.

The Hall Effect mechanism in the distributor, that MasterBlaster suggested you check out, generates a pulse.
The TFI sends this pulse the PIP (profile ignition pick-up) to the EEC.
The EEC after making adjustment to timing, sends the pulse back to the TFI as a SPOUT pulse.

So take the steps suggested and post the results. Then we can buttstuffyze it further.

Re: Iac

Reply #25 –
I fixed the problem. It was the TFI. Now it runs normal, and just in time to go through emissions which is due by tomorrow.