Idle All Over The Place

[DMC5180]

On another car I found someone used too long a bolt to hold the wires on the front, right side of the intake manifold. It crushed the plug on the front of the runner and made a vacuum leak mainly affecting #4 cylinder, leaning it out.

I'm having a hard time seeing how too long a bolt causes a crushed plug.

I'd also like to see a video of you performing a smoke test sometime just so we all understand the process involved.

[David T]

I'm having a hard time seeing how too long a bolt causes a crushed plug.

On the front of each side of the intake manifold is a large freeze-out type of plug. A cupped disk pressed into a large hole. The bolt that holds a bunch of ground wires is tapped into the manifold on the top, right side. If you put too long a bolt in that hole it goes too far and hits the plug bending it and causing a leak.

[DMC5180]

Interesting, who would ever guess that even being possible.

Thanks David

[David T]

Have not done this but probably should. I think AutoZone rents the tester.


Where's the best place to introduce smoke into the system to look for leaks?


I suppose a measured fuel test - i.e. using jars collect a sample from each injector simultaneously and make sure they are equally distributed?
As I said I replaced all the plugs, wires, etc. Did not replace the impulse coil as I was told by a good authority that they almost never go bad. I have not done a spark test on the individual cylinders.


When I tore down the engine 2 years ago I'm pretty sure all the bolts I removed were original. Anything replaced came in a kit from one of the vendors i.e. water pump replacement kit comes with most of the intake bolts, etc.

Based on what you're saying it sounds like I could chase this until the cows come home and never find it. Probably should just chuck it and start over...

I didn't say you could have a bad impulse coil, I said if went bad and was changed and the gaps are messed up on the reluctor the motor will run badly. A bad impulse coil would cause the motor to not run at all. Testing the injectors is more than just fuel flow. A bad pattern can mess up a cylinder too. Did you carefully gap each spark plug the same? Did you put the secondary ignition wires back exactly as they were? Is the distributor cap on all the way? I plug the inlet to the mixture unit and pump smoke in through the hose from the crankcase inlet.

[sdg3205]

I have not... Bought a spare last year as a "just in case" when it popped up here but it turns out it's not the correct one. Different pin configuration on the connectors.
Ugh $345?!?! And what if that doesn't fix it?

Steve

No! Don't buy a new one, but if you've exhausted all other possibilities it only takes 1 minute to swap an idle ECU from a fellow owner.

I seriously doubt its the ECU, but hey who knows. Wouldn't be the first time a new problem came to light. Ask me about my PPR o-ring debacle.

[David T]

No! Don't buy a new one, but if you've exhausted all other possibilities it only takes 1 minute to swap an idle ECU from a fellow owner.

I seriously doubt its the ECU, but hey who knows. Wouldn't be the first time a new problem came to light. Ask me about my PPR o-ring debacle.

I brought up the problem with the bolt because you would never find such an unusual vacuum leak without doing a smoke test. On one car I did when I hooked up, smoke started pouring out of the left/rear pontoon. When we opened it up there was no carbon canister! The hoses were just hanging loose in there. On another car, EVERY injector seal was shooting smoke. Very common to find the air pipe for the idle motor to be leaky too. Another unusual one was no "O" ring on the cold start valve. You could take the whole motor all apart and find this stuff but using a smoke machine is a lot more efficient. Unless you can control ALL of the air going into the motor (meaning NO vacuum leaks!) you will have a hard time getting it to idle correctly and set the mixture. Bad idle ECU's are rare but we have seen cases on this forum where there was a problem with them. Before assuming a bad ECU you should rule out all other possibilities. Even if you do have a bad ECU and replace or fix it, it can't work correctly if you still have other problems like vacuum leaks or things not adjusted properly.

[PJ Grady Inc.]

It's definetly not a bad ECU so don't waste time or money swapping it. Rather than doing compression or leakdown testing (much better indicator of engine health BTW) at this stage of diagnosis I would simply adjust the CO plug allen screw back and forth a half turn or so to see if it stabilizes in either direction. Too rich or too lean will both cause hunting. Ideally the dwellmeter should oscillate back and forth between 40 & 50 degrees when the enrichment is spot on.
Rob Grady

No! Don't buy a new one, but if you've exhausted all other possibilities it only takes 1 minute to swap an idle ECU from a fellow owner.

I seriously doubt its the ECU, but hey who knows. Wouldn't be the first time a new problem came to light. Ask me about my PPR o-ring debacle.

[alexwolf1216]

It's definetly not a bad ECU so don't waste time or money swapping it. Rather than doing compression or leakdown testing (much better indicator of engine health BTW) at this stage of diagnosis I would simply adjust the CO plug allen screw back and forth a half turn or so to see if it stabilizes in either direction. Too rich or too lean will both cause hunting. Ideally the dwellmeter should oscillate back and forth between 40 & 50 degrees when the enrichment is spot on.
Rob Grady

Silly question I know, but where do I connect the leads for the dwell?

[PJ Grady Inc.]

Silly indeed! It's in the tech manual. Shame on you for not having one! You're not supposed to ask questions on info that's readily available ;-) I'm gonna leave that for you to look up.

Silly question I know, but where do I connect the leads for the dwell?

[alexwolf1216]

Silly indeed! It's in the tech manual. Shame on you for not having one! You're not supposed to ask questions on info that's readily available ;-) I'm gonna leave that for you to look up.

Ive got one, but not at work