Ignition Woes

[Corbett]

Looking for some input. Or a decent shop in the Seattle metro area. Apologies for the wall of text as a first post...

Background-1988 Grand Wagoneer. 20 years owned. Maintained at an independent shop as if it were a 5 year old Toyota. Dead stock with the exception of a Howell FI system.

About a year ago it developed an issue where it would randomly die and not immediately restart. This went on for a few months (getting progressively worse) until it just wouldn't start. Traced the no-start to no spark. I already had a spare coil. I purchased a new made in the USA ignition module and a reman distributor.
I installed the distributor first (it was cheaper than the module) and it started. It ran, albeit poorly and was difficult to start. Timing set to 8 degrees. I check a few other things (fuel filter..). Still runs like crap. I bring it to a shop where the owner tells me the distributor was installed wrong; it's not shouldn't have to have vacuum advance hooked up with the mechanical advance. So he disconnects the vacuum advance and says it's mostly fixed. But the spark plug wires are bad, and that's why it runs poorly. It does start right up now, but still drives like crap.

If I reconnect the vacuum advance the truck dies...trying to restart it, it sputters and back-fires ( just like before). It doesn't matter if I connect the advance to the manifold or the port on the TBI.

I'm not opposed to replacing the distributor again (DUI is still made in the USA) I just don't like the idea of throwing parts at it. What am I missing? What can I check or test for?

[tgreese]

Welcome from Massachusetts.

I assume you have the original ignition, with the Motorcraft Duraspark distributor and module? What your mechanic says about mechanical and vacuum advance has to be wrong. The vacuum advance is used together with the mechanical advance in this distributor. A reman Duraspark distributor should work exactly the same as the original.

You realize that the DUI product is a copy of the GM Delco HEI distributor? This is different from the Motorcraft stuff that comes from the factory in these vehicles.

[tgreese]

The '89 TSM is online here https://oljeep.com/edge_parts_man.html Yours is an '88 but it will be the same in all respects other than trim and maybe some emissions pieces.

The '89 TSM is a very large file. Suggest you download it, save it, and open it on your desktop computer or laptop. Knowledge is power. Distributor advance is described at page 8D-33. It shows how to test both the centrifugal advance and vacuum advance parts of the distributor. You need both, and both must work properly.

You also need to set the initial ignition advance at the crankshaft. Typically this is 10 degrees BTDC (before top dead center). This is set with a timing light and the vacuum advance removed and plugged. Loosen the clamp at the base of the distributor and turn the distributor to adjust the initial advance. If you can't turn the distributor to get the initial advance to 10 degrees, the distributor has been inserted wrong.

[Corbett]

I set the timing to 8 per the sticker from Howell. The mechanic set it to 12....2 degrees on either side isn't going to render the vehicle un-drivable.

I have a copy of the FSM and can see timing advance when RPMs are increased...so I'd say the mechanical advance works. I don't have a way to actuate the vacuum advance other than with the vehicle.

And while I understand the DUI is not the duraspark, it is domestically sourced and I'm assuming a higher quality that the China sourced reman.

[Corbett]

I'm also aware the mechanic is wrong-re vacuum advance. He was also nice enough to charge a significant sum of money for his wrong answer, that didn't fix problem he was hired to fix. But that is a topic for another time and place.