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OK, guys. I am reaching the end of my ability. Since I bought my car, I have a consistent misfire on cylinders five, six, and seven. I have pulled the spark plugs from those cylinders, and they are black and slightly wet. This leads me to believe that I am not getting ignition in those cylinders, but that I have fuel in there. Please feel free to correct me if this is a bad assumption. Here is what I have done:
I have taken apart and checked the fuel system. I have a new fuel pump, fuel filter, I cleaned my injectors and checked them for operation, and everything appears to be working. Fuel pressure is good at the rail.
I have checked compression on every cylinder. They are all at 150 psi. This was done with a compression gauge while cranking the starter. That is the only way I know of to check compression.
I have spark at all cylinders, but it is a little weak. I have replaced the plugs, wires, cap, rotor, ICM, And ignition coil. The previous owner also replaced the distributor not long before selling to me. I took the car to a shop in my town, and the owner took a look at it with me. He pulled the spark plug wires off of the cap and listened to the spark there. He said the miss firing cylinders sound a little week at the cap. What would cause a weak spark on only certain cylinders, at the distributor cap?
Another note the shop owner gave me, is that if the rocker arms are worn, it can cause bad compression in a cylinder that would not show up on a compression test.
I have, at best, limited mechanical knowledge. This is by far the most I have ever done to work on a car. I honestly passed the end of my ability a while ago. I love learning new skills, but this is becoming beyond me. Can anyone help?
Last edited by Bfenty; 05-03-2017 at 10:12 AM.
Reason: fat finger typing
has anybody heard of a worn out distributor shaft or worn-out drive gear or worn out bushing or something causing a repetitive wobble in the distributor which would create a miss at the same points on the distributor cap on every rotation?
has anybody ever seen that connected to a repeating misfire?
The three cylinders that are misfiring are sequential in the firing order, so if there's a bad spot on the pickup coil, could that cause a weak spark? Or is it all or nothing with the pickup coil?
Did you check the order on the distributor also. Trust me I have done this.
Now I'm a little confused-can the order change on the distributor? I've got the correct spark plugs connected to the correct places on the distributor cap, is there more to it than that?
remember its not sequential. if your posts are '5-6-7' they are wrong.
Sorry, I just meant they fire back to back, making it seem like something is skipping on the firing order. I find that a little odd that three cylinders in a row on the firing order are the ones misfiring. I mean, that could be coincidental but I think it's worth thinking about.
..... How did you determine that those particular cylinders are mis-firing ? ... aside from the black and wet spark plug observation ? ... Can you feel it when driving ? ... at what rpm/gear range ? ... at idle ? ... fuel economy ? .....
the symptoms, and avenues of resolution seem logical, but I too believe you have a problem with the pickup coil, OR a problem with the distributor itself. Have you pulled the distributor, checked the drive gear?, Is there a distinct wobble in the distributor shaft when out of the engine? as you've changed everything else, Plugs, Wires, Cap, Coil. It is not the compression, but with the plugs wet as you said, you are not getting spark at those 3 cylinders. I would pull & check the distributor.
..... How did you determine that those particular cylinders are mis-firing ? ... aside from the black and wet spark plug observation ? ... Can you feel it when driving ? ... at what rpm/gear range ? ... at idle ? ... fuel economy ? .....
Couple things here:
First, it's OBVIOUS. You can hear it even at idle. At 1500 RPM it's really bad, but as I've gotten used to the car I can feel it across the entire spectrum. It's less noticeable at higher RPMs but that's normal.
I've also pulled the plugs on the injectors while the engine was idling. There's a noticeable difference on every other cylinder, but those 3 there is not a difference in how the engine runs. Thus, they were already not firing.
Third, I did the trick where I ran it for about a minute then felt the exhaust. You can tell which cylinders aren't firing because the exhaust headers are cold coming out from them. There's a very noticeable difference in how hot they were just by touch.
the symptoms, and avenues of resolution seem logical, but I too believe you have a problem with the pickup coil, OR a problem with the distributor itself. Have you pulled the distributor, checked the drive gear? Is there a distinct wobble in the distributor shaft when out of the engine? as you've changed everything else, Plugs, Wires, Cap, Coil. It is not the compression, but with the plugs wet as you said, you are not getting spark at those 3 cylinders. I would pull & check the distributor.
D.
I will probably try to pull the distributor either tonight or tomorrow, and I'll let you know what I find. I am thinking a new distributor is a good idea.
What are signs of a bad distributor? What can go wrong with them? I understand the concept of how they work but I've never taken one out before, so I don't know what I'm looking for. I'd hate to buy a new one, as they're pretty expensive if there's nothing wrong with the one I have.
Also, the pickup coil is distinct from the ignition coil, right? Because I did replace that already.
crash, that is some nice reading. I'm travelling on business and I think that's what I'm gonna read in my hotel room!My question about the pick up coil, is can the pick up coil have weak points in its circumference that would result in a week charge being sent down line to certain positions on the distributors circular path.
can the pick up coil have weak points in its circumference that would result in a week charge being sent down line to certain positions on the distributors circular path.
The pickup coil doesn't have anything to do with the ignition sequence. Its only job is to trigger the ignition coil eight times per distributor revolution. It's the rotors job to send those ignition pulses to the correct distributor cap post.
Think "old school". Do the ignition points know which cylinder they are firing? Same-o same-o.
For an odd-ball test, pull the dist. and rotate the rotor 180*. With the rotor pointed at 180* from the original position, and the dist. body back in its original position, re-route the plug wires to get the firing order correct. (#1 wire at #6 position, #8 wire at #5 position, etc.). The ICM is still in its original orientation. Does the car run any different?
05-03-2017, 09:33 AM
TPI 3 cylinders consistently misfiring
