Troubleshooting .. perhaps this may help some one (1 Viewer)

[jetmutant]

Hey all, Long time lurker here mostly ..

Anyhow I have a 78 FJ40 that I am slowly resto modding, it has a stock 2F with header, Weber 32/36 carb and an HEI ignition. Runs pretty good ... now but i did go through an extended period of hair pulling recently.

The issue was that it would run great until about 2800 rpm then act like it was starving for fuel and just would not get past 60mph up hill. Soooo I spent a week tearing apart the carb and cleaning all jets, soaking the carb blowing out all the orifices. no help then I replaced all the fuel lines, and to further ad to the noise I had to replace the fuel pump recently because it was leaking oil on the ground and fuel into the oil, since I am going to go to TBI soon I chose an electric pump. again no help.

Next was ignition, I replaced main coil, spark plugs, wires and suspected the module .. replaced .. no help.
finally took apart the distributor to get at the pick up coil that is under the rotor, I think the NAPA echlin part # is MP104.. it fits a 1979 chev pick-up or Camaro that had HEI with a 6 Cyl .. Success! Seems the wires that go to the stator flex as the advance moves through the cycle and eventually break or the coil itself will suffer a failure from the vibration, at any rate this replacement fixed my beasty, and perhaps may help someone else with similar issue.

 

[DougAustinTx]

Really good info here. That is the sort of defect that can drive you crazy. Thanks!

 

[78fj40mg]

Great troubleshooting work!
Thanks for posting this to help others with similar symptoms, just one problem tough to make your topic searchable you need to change the title describing your issue.
Cheers!

 

[honk]

... now but i did go through an extended period of hair pulling recently.

The issue was that it would run great until about 2800 rpm then act like it was starving for fuel and just would not get past 60mph up hill. Soooo I spent a week tearing apart the carb and cleaning all jets, soaking the carb blowing out all the orifices. no help then I replaced all the fuel lines, and to further ad to the noise I had to replace the fuel pump recently because it was leaking oil on the ground and fuel into the oil, since I am going to go to TBI soon I chose an electric pump. again no help.

Next was ignition, I replaced main coil, spark plugs, wires and suspected the module .. replaced .. no help.
finally took apart the distributor to get at the pick up coil that is under the rotor, I think the NAPA echlin part # is MP104.. it fits a 1979 chev pick-up or Camaro that had HEI with a 6 Cyl .. Success! Seems the wires that go to the stator flex as the advance moves through the cycle and eventually break or the coil itself will suffer a failure from the vibration, at any rate this replacement fixed my beasty, and perhaps may help someone else with similar issue.

I'm glad for you that the problem is solved and you're back to good running.

Think how much more satisfying it would be to have worked a troubleshooting plan based on the knowledge of the involved systems instead of working through an expensive process of elimination by changing or rebuilding (carb) parts until one of them resolved the problem.

 

[jetmutant]

I do have a pretty thorough knowledge of the systems involved, the real problem is that it seemed to manifest itself as a fuel issue instead of an ignition issue. with all the other factors involved prior to this cropping up all of the things I did was (to me) a logical progression of a fuel issue. Then moving to an ignition issue.

Oh and I can't seem to find a way to modify the title? Anyone able to help with that?

 

[honk]

I do have a pretty thorough knowledge of the systems involved, the real problem is that it seemed to manifest itself as a fuel issue instead of an ignition issue. with all the other factors involved prior to this cropping up all of the things I did was (to me) a logical progression of a fuel issue. Then moving to an ignition issue.

Oh and I can't seem to find a way to modify the title? Anyone able to help with that?

I don't think the title can be changed except by one of the mods but it doesn't really matter.

Going back a lot of years I worked for a while as a mechanic for a place that had a lot of vehicles all alike, over 2000 of them. They all had point systems just like an older Chevy distributor. We had every kind of problem imaginable but one that got me good was a vehicle that seemed to have bad gas. It sometimes was hard to start, sometimes would do like yours did, sometimes would just start running crappy after being seemingly fine for a couple of hours.

I went from the intank filter to changing the tank and the fuel lines. Then into the one barrel carb. Finally it seemed to be good and I released it. But it was back the next day with similar complaint. I was getting beside myself until one of the older longtime guys asked me if I'd changed the condenser.

Huh? I thought he was nuts or pulling my leg but at the time I didn't have a better idea so I put in a new condenser. I never saw the truck in the shop again. Even now it doesn't seem sensible but once in awhile it would happen to one of that model. They can heat and short the point plate, or something.


The point of this overlong diatribe is this: When I'm sure I know what's wrong I like to take a few minutes and ask myself "Yeah, but what else COULD it be?". Couple that with the maxim that whenever you're taking best guesses you should always start with the cheapest possibility. Let increasing experience build up. We'll never know it all and anyone who thinks they do will be stumped before long.

 

[jetmutant]

I agree Honk, I have been a mechanic for nearly 35 years worked on everything from VW's to Lamborghini and for the last bunch of years been an A&P/avionics tech for a major airline. Sometimes what you know can get in the way of what is really wrong. In my troubleshooting of this issue I started with the fuel because it acted like perhaps the new pump was not supplying enough fuel/pressure at speed, checked that with fuel pressure gauges. not that so then thought Hmm perhaps old lines were collapsing internally (had that happen before, and they were kinda nasty looking anyway so I changed them .. again no help. Then me thinks .. hmm could be that there is a clogged in tank filter ... looked inside with boroscope .. nops no has intank filter .. hmmm perhaps there is clogged jet or internal passage in carb, it was ratty looking as well so I pulled it off and thoroughly cleaned/rebuilt it ... again no help, so then I started looking at the cap, thought perhaps carbon tracing could start conducting at certain RPM, cap, rotor, plugs and wires needed replacing anyway so they got done ... still no help. Gurus on Chev boards said could be HEI main coil, I had checked that with meter but thought since it was fairly cheap I changed it (next easiest thing) .. it was a little better but still not right, so I started in looking at the pick up coil, I had tested per manual but hadn't flexed the wires when I did it, when I flexed the wires I got minor fluctuations in my readings .. pulled apart distributor and changed the pick up coil and walla walla all better. So there you have my process of elimination .. Just hope this helps someone else stumped by a problem that acts like fuel starvation but is really and electronic ignition problem.

I just added a bunch of tags to the title so someone searching may find it.