HELP Intermittent no-start. Opinions?

[brrian]

81 GP, 231 V6. Lots of the engine components are new, including a (rebuilt) carb, ignition module, coil, & battery.

For the year that I've owned it, it's started and run fine, except twice:

Once about three weeks ago - I drove it 2 miles to the store and when I came out it wouldn't start. I left it there for a couple of hours, then went back and tapped on the carb (I'll get to why) - then it started & I drove it home.

Yesterday I moved it about 100 feet & parked it in my driveway. An hour later it wouldn't start. I tapped on the carb again & it still wouldn't start. I tried starting it 2 more times throughout the day & still no. Then I tried this morning and it started right up.

About a month ago I put a half can of Berryman B12 in the gas tank. I deduced that it might have loosened up some stuff that made its way to the carb, clogged something & caused the issue - and that I loosened/cleared the blockage by tapping on the carb. I hadn't tried starting it prior to tapping on the carb, so it might have started anyway).

I had hoped it wouldn't start this morning so I could troubleshoot. I don't feel like spark is the issue but I planned to check & confirm.

I'm planning to install an inline fuel filter down at the bottom of the engine so I can see what the gas looks like.

What's your opinions of this? Does fuel blockage make sense as a possible cause of this? What else might cause this, then fix itself? Now that it's running, any suggestions of things to check?

 

[pagrunt]

Guessing it cranks. If it is blockage in the fuel line, start cheap with a new fuel filter & clean out what you can from the line. Might be a good idea to have the line blown out (in a safe way) to clear anything in it. Make sure the feed part of the system is clear before moving up to the next possible cause.

 

[Ernest]

Ok, new ignitiontion module, so i gotta ask.... what thermal paste did you use?

Many people make the honest mistake of using the clear looking gel like material that typically comes with new ignition modules, thats a big no no, thats dielectric grease, its an insulator to keep moisture out from electrical components.

What i use when replacing ignition modules, is DOW 340 heat sink compound, good for up to 350F and requires no cure time, or you can use the same type used for CPUs in computers if you've got that stuff handy, either will work as intended to make sure you IGM live s along and healthy life, when they start going faulty, they can give you similar starting issues as well.

 

[BlairC_789]

It sounded like vapor lock from a fuel line being to close to exhaust or something but then you mentioned the time it wasnt starting all day

 

[brrian]

Ok, new ignition module, so i gotta ask.... what thermal paste did you use?

I used the clear-ish gel. It says to in the instructions though... "Apply a liberal coating of the enclosed silicone compound to the module's metal mounting plate, to prevent damaging heat buildup". I wouldn't have known any better. Why would they include that & tell people to use it? Bizarre.

I just went down the HEI ignition module rabbit hole. Tons of issues with these, lots related to improper heatsinking & poor quality aftermarket parts (i have both!). So, this is getting fixed. I'll put in an ACDelco module.

I also read that you can troubleshoot a failing module with a tachometer - that if you hook up a tach & it doesn't move while cranking, that's a clue that it's bad. Have you heard of that?

 

[Ernest]

No clue about watching the tach0meter for movement while cranking to check for a possibly bad IGM.

Just get the proper THERMAL paste needed, its a tight clearence between the module and mounting surface of the distributor, so just spread and a very small and even amount, with a credit card, id card, drivers license, etc and not with a finger across the whole metal backside surface of the module, if done right, you should see a very tiny amount squish out from all sides.

 

[CopperNick]

Thermal Paste Y'say? Good to know.

As for the fuel? problem, have you been able to detach the fuel line from the carb and do a cranking test to see how much fuel is being delivered by the pump into a measured container over a set amount of time? Engine driven fuel pump typically feeds fuel in the range of 4-7 psi plus or minus; anything greater and the carb can get damaged by gasket blowout.

Your ongoing description of having to tap on the carb kind of makes me wonder if you have float needle sticking in the closed position and when the float drops to allow more fuel to enter the fuel bowl, the needle isn't lifting off its seat. Failing that, some of that crap from the tank that your Berryman additive might have dislodged is stuck in the needle passage and tapping pops it free, temporarily.

The Rabbit Hole here may be a complete take down of the fuel system from the tank forward and give the tank a good washout if you think ossified gasoline is your culprit.

Nick

 

[brrian]

I haven't disconnected the fuel line yet. I posted here first for opinions & I'm glad I did because the ICM seems as likely a cause as a fuel issue. I'm hoping it happens again so I can troubleshoot the ICM first. I'll replace it no matter what but if it's not the culprit I'll work on the fuel system next.

The first time it happened I didn't try starting it until after tapping on the carb. It might have started without touching the carb. I just cared about getting it home.

Thanks for the responses!

 

[Ernest]

Thermal paste/grease/compound.... its known by those that use it by different names.

The DOW 340 i use - https://www.amazon.com/dp/B00D0HVYHI/?tag=gbody-20

 

[brrian]

It happened again. I started it - it started right up, nice and clean. I drove it around the block, then parked it in front of the house. A half hour later I tried starting it & it wouldn't start. Prepared this time, I checked spark & it's fine. It's flooding. I held the pedal to the floor & cranked it & it sputtered to life. Chugging, barely running then eventually settled down. I don't know why it would flood after it sits for a while like this? Fortunately, it's going to my mechanic tomorrow.