HELP!! Chrysler 360 Engine Idle issue. - The Hull Truth

AlexisMarie · 08-29-2007, 09:09 AM

I know there is a huge amount of knowledge on this forum so I will try my best to tap into it. Thanks in advance for any suggestions.

This problem has stumped me and I dont know what to look at next. I will explain the best I can. They are twin 360's(electronic ignition) in a 1972 Luhrs which seem to be original. They both Ran perfect all summer. I let the boat sit for 2 weeks then when I started the port engine it ran like crap. The idle was very ruff and it seems to be missing(no backfires). If you give it gas and raise the idle it seems fine. Its very obvious while idling. These are the steps I already completed.
1- Replaced Cap and Rotor.
2- Checked and replaced spark plugs(none were fouled)
3- Changed Wires.
4- Swapped ECU's from good running starboard engine.
5- Replaced Fuel filters and ran engine from 5 gallon containier of good fresh gas.
6- Replaced carb with good used one. I put the old one back after test.
7- Checked PVC valve.
8- Checked alternator for proper output. Good.

One strange thing I noticed. While checking the timing the strobe lite was erratic and was not a steady blinking lite. And the timing was way off. Unfortunately, I didnt have the tools with me last night to loosen the distributor to try and adjust it back to specs to see the response.
I double checked the firing order and ensured no wires are crossed.

What can cause the timing to be so inconsistent and erratic. My last ditch effort is to swap the distributor and coil.

I AM STUMPED!!! ANY Ideas would be appreciated.

Thanks.

randall · 08-29-2007, 09:44 AM

i have the same engines so im interested......did adjusting the timing fix the problem?.....also if one engine is counter rotating dont forget that when doing the timing......i did that once...its not pretty

AlexisMarie · 08-29-2007, 09:54 AM

Quote:

randall - 8/29/2007 8:44 AM

i have the same engines so im interested......did adjusting the timing fix the problem?.....also if one engine is counter rotating dont forget that when doing the timing......i did that once...its not pretty

I will try adjusting the timing this evening but I dont think that will do the trick. That wouldnt cause the timing to be so erratic(I think). Besides, something must have happened to knock the timing out of whack in th first place. The distributor was tight and was not moved. I am hoping the timing chain didnt skip a tooth. I am aware of the reverse rotation on the SB engine. I will keep you posted.

Franco · 08-29-2007, 10:03 AM

I spent several years as a Chrysler Technician at car dealerships, maybe I can help some.

If you can get a few tools together, a tachometer and a vacum gauge.
connect the vacum gauge and tach to the good running engine an note the vacum and rpm at idle.

Now connect the to the rough running engine, the vacum gauge should be steady, but I bet the gauge wil be bouncing right now, the rpm will probably be a bit erratic also. Now comes the trick part, get a pair of needle nose pliers or spark plug pliers and one at a time pull the plug wire off each plug. If that cylinder is running good, you will notice that the vacum gauge and tach become more erratic. When you hit the cylinder(s) that are running badly, you will see no or almost no change on the tach and vac gauge. That will narrow it down quickly. I suspect that you may have a vacum leak some where. You can take a spray bottle full of watter and spray around the intake manifold and carb base and see if the engine smooths out. If it was a car, my first guess would be an EGR valve is either bad or stuck. I don't know if your boat has an egr valve.

You can pm me if you need more help

richinct · 08-29-2007, 10:14 AM

Check the centrifical advance in the distributer, make sure it is free and the weights are not sticking, springs rusted

andyp262 · 08-29-2007, 10:17 AM

whoa! hold on! first off, it is impossible for the timing chain to skip a tooth. i have been an engine builder for 25 years. it doesnt happen. secondly, if the clamp on the distributor is tight then the timing should not have changed. does it have vacuum or mechanical advance? it is possible that the distributor shaft is bent. on small block chryslers the distributor drive gear also runs the oil pump. you need to check for vaccum leaks as well and also consider a compression test. that is where i would start. good luck

AlexisMarie · 08-29-2007, 10:55 AM

Quote:

Franco - 8/29/2007 9:03 AM

I spent several years as a Chrysler Technician at car dealerships, maybe I can help some.

If you can get a few tools together, a tachometer and a vacum gauge.
connect the vacum gauge and tach to the good running engine an note the vacum and rpm at idle.

Now connect the to the rough running engine, the vacum gauge should be steady, but I bet the gauge wil be bouncing right now, the rpm will probably be a bit erratic also. Now comes the trick part, get a pair of needle nose pliers or spark plug pliers and one at a time pull the plug wire off each plug. If that cylinder is running good, you will notice that the vacum gauge and tach become more erratic. When you hit the cylinder(s) that are running badly, you will see no or almost no change on the tach and vac gauge. That will narrow it down quickly. I suspect that you may have a vacum leak some where. You can take a spray bottle full of watter and spray around the intake manifold and carb base and see if the engine smooths out. If it was a car, my first guess would be an EGR valve is either bad or stuck. I don't know if your boat has an egr valve.

You can pm me if you need more help

THere is no EGR valve. I will try that spray bottle technique before I try the other steps you mentioned. I did try pulling and grounding one wire at a time and listened for noticable difference but it seems there was no difference when I pulled one plug wire at a time(I guess the tach would have showed it). Thanks for the suggestions.

Franco · 08-30-2007, 12:02 AM

Any progress with the rough running?

grouse ridge · 08-30-2007, 02:22 PM

If there is not a vacum leak. It will most likely be the idle passage clogged with carbon. This is comon on any carb.

slickster · 08-30-2007, 04:03 PM

Let's try a diagnostic procedure instead of hit and miss.....with the engine warmed up and running....a pair of plastic pliers or insulated pliers....remove one ignition wire at a time and try to find the one that doesn't affect the rpm's when you remove it....when you do, that is the suspect cylinder....pull the plug and check compression, (kill the ignition)....if it's good...check for spark....a screwdriver up the wire to ground...should be a nice, fat spark....then check for vacuum leak by spraying small amounts of wd 40 around suspect areas.....things that are common to older mopars....distributor bushing wear causes lumpy idle, poor spark, inconsistent gap at reluctor....worn cam causes valves to barely open....double/triple check firing order...you've have it apart, make sure it's correct....good luck, keep us posted....Mick

AlexisMarie · 08-30-2007, 05:07 PM

PROBLEM SOLVED. It was the timing. I dont know why and how it was way off but once it was adjusted back within specs it ran fine. Unfortunatley, I didnt have the right wrench to loosen the distributor a few nights ago.I dont know what could have casued it to substantailly retard but after adjustment its perfect now. Thanks for all the input. I learned a few new things in this post.

slickster · 08-30-2007, 08:09 PM

Check the mechanical advance mechanism....it might be corroded and hanging up....Mick