Car Misfires And Tach Jumps Around

mob · Jul 24, 2012

OK guys, I am pretty angry. My car has been having problems for months now. Started out of no where. This is not a daily driver so it sits for a while. On first start up I drive it and everything seems fine. After driving a little bit the car starts misfiring really bad when maintaining a constant speed, under acceleration it smooths out but in higher rpms it also cuts out. The other thing is the tach jumps around like crazy, fluctuates about 500-1000rpm at a constant speed, jumping around all over the place.

I've changed the distributor with a new PIP and TFI module TWICE, I've put TWO new coils on it. I redid the electrical plug to the coil.

I've checked resistance on the coil and it checks out perfect, I've check the electrical wires from the coil to the TFI and they are both solid, I've checked coil ground and its good.

The spark plugs are brand new, and the old ones didnt look bad. The plug wires probably have 200 miles on them, they are MSD universal fit wires. The car worked perfect with all these parts before and all of a sudden it started doing this. The only thing I can think of I havent changed since these problems started is a new set of wires, and a new computer which I replaced about a year ago with a reman.

Also I checked resistance on the wires, and they all are about 1000-1200 ohms.

I am lost... The car only misfires when the tachometer jumps around, they go hand and hand, its not one or the other, are there any other things that can cause this to happen other then ignition related parts? TPS? Ignition switch? etc.

I've checked codes and got nothing.

jrichker · Jul 25, 2012

Are there any other electrical items malfunctioning?
Does the engine temp gauge rise when you add electrical load like, lights, HVAC blower, etc?
Have you had the electrical system load tested with a warm engine?

mob · Jul 25, 2012

The car runs a little bit hot, but is constant, it stays at about the "O" in "NORMAL". What exactly do you mean by electrical system load test. Like on the battery? Or the Charging system? I've had the charging system checked out recently and it's charging just fine. I replaced the ignition switch about a year ago, if that has gone bad could it cause intermittent problems like that? I really dont know where else to look, I am considering getting my money back on the reman dizzy and getting one from somewhere else but I dont think that will solve it. I've had the TFI module checked and its good, PIP looks brand new in the new dizzy.

jrichker · Jul 25, 2012

What I am after is any change in the alternator output voltage with a change in load.

The other possible problem is a bad engine block to body ground. As you add load like, lights HVAC fan, wipers, etc, the ground can start to cause a voltage drop across it. The tip off is that the temp indicator rises and falls with changes in the electrical load. Because the engine temp circuit uses the engine to body ground as a return path for the indicator signal, it is dependent on the engine to body ground. The voltage drop across the defective ground is seen by the engine temp circuit and causes the indicator readings to change.

mob · Jul 25, 2012

I see what you're saying Joe, but the engine ground is good, I have a 2ga wire going to the body that is less than a foot long. I dont have A/C either, the car does this with no loads on, no wipers, lights, no radio, no a/c, using stock fan clutch. I just checked the ground to make sure it is still solid and tight and it is, also dumped the codes again and got nothing but emission codes due to lack of EGR and Smog. Any other ideas? I am fresh out, literally about to go drop it off to someone who knows more than I do. Is it possible the TFI can act intermittently when it heats up, I remember when I first changed it there was some white stuff on the back of the TFI does that need to be there? I've had it checked but when it was cold.

Could the wires be bad even though the resistance checks out?

Also I have the coil electrical wires running alongside the 2ga power cable from the battery, only thing separating them is tape, and wire loom, could that cause any interference?

jrichker · Jul 26, 2012

The white stuff was heat sink compound. It is important that it is there and spread evenly. It helps keep the TFI module from overheating. If the TFI overheats, you could have problems like the ones you are describing.

mob · Jul 26, 2012

Joe, where can I get that from, Radio Shack? And how much should I use? I think I am going to try and replace the TFI one more time and make sure I use new compound this time. Thanks.

Chuckman · Jul 26, 2012

mob said:
Joe, where can I get that from, Radio Shack? And how much should I use? I think I am going to try and replace the TFI one more time and make sure I use new compound this time. Thanks.

shack should have it, or if you have any friends that build computers, borrow a tube of arctic silver. the tfi i bought a couple months ago also came with two packets of its own stuff, just spread it out on the metal on the back of the tfi.

mob · Jul 26, 2012

Ok cool, I picked up the cheap heat sink compound stuff from radio shack today for a couple bucks just in case, do you think I should go back and get the artic silver thermal compound? I ordered a new TFI from the parts store but it looks like it just has a packet of dielectric grease in there, i'd rather use something better. I really want to get the best stuff I can get so I only have to do this once. I just pulled the dizzy and took off the TFI and saw there is only a little bit of residue left on there. So whats the best stuff for this purpose, the arctic silver thermal compound or just regular cheap heat sink compound. Thanks guys, I am almost positive this is my issue.

mob · Jul 26, 2012

This is how much was on there.

mob · Jul 30, 2012

So I changed the TFI module and it seemed to be working perfect but after about 15 minutes of driving slightly different issue came up, it will start to lunge back and forth pretty bad, it feels weird not so much like a misfire or cutting out, just lunging back and forth, and when I brake hard the car will stall. Any ideas? I put a new TFI module on it and coated it pretty well with thermal compound, I didnt use the arctic silver but the regular thermal compound radio shack has.

jrichker · Jul 30, 2012

The Radio Shack stuff should be OK.

What do you get for codes with the new problem?

mob · Jul 30, 2012

I was going to check the codes again tonight and see if anything new is on there, I'll let you know later tonight.

mob · Jul 30, 2012

Joe, just a thought, could the issue with TFI caused the PIP to go bad? The issue it is having is almost like it is running out of gas, the PIP controls the injectors right? So maybe they are not firing correctly?

jrichker · Jul 30, 2012

mob said:
Joe, just a thought, could the issue with TFI caused the PIP to go bad? The issue it is having is almost like it is running out of gas, the PIP controls the injectors right? So maybe they are not firing correctly?

Get out your noid injector tester and plug it into an easily accessible fuel injector harness connector. Also look for code 14 when you dump the codes.

mob · Jul 30, 2012

Hey Joe, I guess it would have helped if I had opened the hood and inspected the motor after this happened but I was too upset and just parked it and came inside. I opened the hood and apparently my power steering cap went missing and was shooting tranny fluid all around. Nothing is soaked but there is a thin film on the dizzy and tfi, and kinda puddled on the timing cover, also shot around the coil area. I guess its probably a stupid question to ask if this is my issue but does this sound right? Everything just seemed pretty sealed so I am not sure what exactly got soaked, I opened up the dizzy and it looked pretty clean in there, maybe just a little wet. Should I just try and clean everything up? Or should I just go ahead and swap out the dizzy and TFI one more time?

Codes yielded the same results.

jrichker · Jul 31, 2012

You're going to have to clean it up anyway, to start there first....

Use some mineral spirits from Ace hardware or Home Depot if the stuff hasn't gotten unreasonably expensive.

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