Generac with an attitude

[Gunny]

97 model with 7.4L GM

Started with a problem with the fan drive, one of those odd ones with the shaft running through the radiator, gear box on the other end so the engine can run in the power band. Lovejoy coupling came apart and trashed everything in front of the radiator. Fixed all of that and now no start.

I'm a diesel person but thought I had these things figured out. No fire from any of the plugs. Getting 12VDC to the coil. Pulled the cap and we have rotation. Removed the HEI module and off to Advance. Checked bad, installed a new one. Still no fire. Ohmed the trigger, 840 ohms. Makes a little over .5 VAC when cranking (auto parts store man says that is good, suggested a bad coil) Bad coils are few and far in between but since they are $17.00, hung a new one on. Same song, no fire. Can't buy the trigger (cam position sensor/device that signals the HEI when to fire) alone, got to buy a whole distributor.

Thoughts/comments/recommendations from the experts?

[Douglas]

Not sure if this is the same part but I see no harm in taking a trip to the local recylcer or repair shop and seeing if they have some HEI distributors around you can have. Odds are you can strip out the parts you need.

I had a 305 in a 1984 GMC 1/2 ton that developed a problem like you discribe and it turned out to be the pick up coil was failing making it hard to start untill one day it didn't. I just swapped out the entire distibutor from another used small block and never looked back

[Jim Rankin]

Don't they have a crank position sensor? Possibly damaged by the failure? One reason for a sudden death if so equipped.

[PFT]

Gunny, I remember in the early days of HEI they would burn thru the rotor under the center tab that contacted the coil output. The spark then went to the shaft under the rotor.
Just a thought, and has no relation to your original problem.
Good luck, PT

[Gunny]

Paul:

Thought about that too. Pulled the wire from the coil off of the distributor cap and plugged in a spark plug, laid it on the intake manifold and no spark.

[BDMelon]

just a question does this HEI system, is this the older one with vacuum advance on dist. ? if so
the wire on the pick -up may be broken under the pick up coil, wire get rub through , or the flex of the advance
unit after some time, break wire off the soldering point.. just my to cents worth

[K D Redd]

I would have to check a HEI pick-up coil at the shop BUT I think 840 ohms is way to high. Go to you local part store with YOUR ohm meter and have them pull one of the shelf and OHM it. I think it should be closer to 150 ohms. The HEI chip can be triggered with other pick-up coil as I am using a HEI chip with a standard NON-resistor coil and a Chrysler electronic distributor in my old 1967 Dodge 400 truck. The reason I did the ignition system that way was the wireing was much simpler than the Chrysler system.

Kent

[Gunny]

Kent:

You are correct. Did some more research this morning. Monday going to dig up a new pickup coil or another distributor. I'll post the results.

BDMelon:
This is on a genset. They run at a fixed RPM, no vacum advance. The only moving part in the distributor is the shaft and anything afixed to it.

Sort of suspicious as a few other things on this machine have been seriously jury rigged and it shows other evidence of someone's work that tells me they didn't know what they were doing.

[pegasuspinto]

is this one of the self-contained HEI distributors, with the coil in the cap, or a seperate coil and distributor? You can get ANY component part for the coil-in cap GM HEI units. I kept a complete set of spare bits in my motorhome. I wouldn't of thought anyone would bother putting the later Fuel Injection HEI units on a genset.

Robert

[Tom Kilgore]

cam pos sensor lx756 standard ign brand, crankshaft position sensor pc123t I think,I know these are correct for gm trucks

[K D Redd]

Gunny,
I do not know if I was correct or not. Yesterday aftenoon after I got back with my combind header, I measured a HEI pick-up coil from a computor controlled, NO Mechanical/Vacuum Advance HEI. It read 850 ohms. This unit was a junker and the pick-up is of unknown quaility.

Kent

Originally Posted by Gunny

Kent:

You are correct. Did some more research this morning. Monday going to dig up a new pickup coil or another distributor. I'll post the results.

BDMelon:
This is on a genset. They run at a fixed RPM, no vacum advance. The only moving part in the distributor is the shaft and anything afixed to it.

Sort of suspicious as a few other things on this machine have been seriously jury rigged and it shows other evidence of someone's work that tells me they didn't know what they were doing.

[Gunny]

New one at NAPA ohms at 790 ohms.

Also retested the HEI, the one that Advance tested as bad, it tested good this time.

Now I'm gonna have to scratch my head and think.

[Wayne 440]

I have nothing meaningful to add, just wanted to express condolences. Now others know why there are so many gen-set stories that start with "It was about 3 pm on Friday afternoon, and we had this #%$@* Generac that..."

[rrfxxxr]

Originally Posted by Wayne 440

I have nothing meaningful to add, just wanted to express condolences. Now others know why there are so many gen-set stories that start with "It was about 3 pm on Friday afternoon, and we had this #%$@* Generac that..."

Heh heh I heard that. We had a few, didn't hold up too well. The 3.5kW Honda units we had were better. (if you let the carb run dry when you shut them down.)
Sbw

[Billy J Shafer]

Gunny. Why are you waisting your time on junk. Saw one of those units down here last week. Shaft came off and took out the whole front end. Told the coustomer to go buy a kohler. Engine is trashed anyway. They have a pit on site and I think that is going to be its new home.

[K D Redd]

Gunny,

Did you ever get the HEI figured out?

Kent

[Gunny]

Well.........yes.

I wanted to go with an old style distributor, one wire with the coil in the cap. Ran into a snag with that, service manager vetoed that idea, the genset is at a nursing home, life safety and liability issues so had to be OEM replacement.

Got a new one from GM and got pulled off the job. New distributor was installed by someone else and still no fire. Back on the job. Seems there is a resistor in the wiring harness that ohms OK but when there is a load on it, goes open. Generac claimed its a GM resistor and GM denies any knowledge of its existance. 8 ohm resistor. Found a 5 ohm 20 watt resistor in my "bag" of spare parts, extra washers, screws, relays, fuses, good used parts and smoke restorer. Up and running just fine now.

Remembered something passed on to me many years ago by a real wise gas engine man. Best way to time a fixed speed dry fuel engine is with a vacum gage. Let it run and warm up with a vacum gage on the intake, adjust the timing to get the highest vacum reading, bolt it down and call it done.

[K D Redd]

Gunny,

Ate you saying this resistor is in the 12 volt feed wire for the HEI? In GM cars and the one half GM, one half Chrysler system I have on my old Dodge 400 Fescue seed truck you DO NOT use a resistor in the feed line between the ignition switch and the HEI 12 volt input. That is the beauty of the system, No resitor to burn out.

Kent