Question for SBC guys!!!

[FJKai]

I'm running a SBC 400 with an HEI dizzy (old skool, 4bbl carb). I recently had the ignition module die about 2 months ago (no probs with it for the 2+ years I've had it), no prob, got a new one from Napa and all's good. I recently have now been having a stall out issue once I run it for a bit. It seems to die after it's gets "warmer" than normal after pulling a hill or in extreme outside heat days. If I let it sit for a while to cool down, it will fire back up and run. The first thought like most, vapor lock right? Problem is it has never had a vapor lock problem before, fuel line is not near the exhaust, and etc. I've heard some guys talk of "intermittent hei ignition failure due to heat." Is that possible? I mean, this problem all started after a failed ignition module was replaced. I've had the replaced module tested and they said it checks out fine. Possibly cheap ignition module from Napa? Try a GM module? No friggin way, it either works or it doesn't? Anyone experience this type of symptom? I'm tempted to re-route the fuel line and add a bigger carb spacer between the intake manifold just to rule out the vapor lock possibility, but if there is a possibility of ignition failure due to heat, then I'll go with another module. Oh yeah, this thing runs at about 190 degrees almost all the time, slightly hotter when pulling a long hill, or once it's turned off on an extreme hot day after running for a while. Just need some expert advice. Thanks.

 

[FL cruiser]

I've had that happen before. Ignition module only fails when hot. replaced module, problem solved.

 

[Elbert]

The modules normally last for a long time. You did use the grease that comes with it for the install?
It does sound like a vapor lock, but you could check that with a "spark test" at the plug wire to see if you have "spark / power" at the plugs when the truck dies. Guess you are running a mechanical fuel pump? If you have fire at the plug wire when it stops running then I would suspect vapor lock type issue, it not then if you don't have fire at the plug wire when it stops running....may be the module.

 

[cody c]

would adding insulation to your fuel lines help, instead of moving it

 

[FJKai]

I've never checked for spark once it died, but next time I'll remember that. I did use the heat sink grease, I went one step above and bought some real heat sink (not the vaseline they give you with the new module) from Radio Shack and it still died once good and hot. If I end up re-running a fuel line you can bet it will be wrapped with some type of heat sheild wrap just in case. Yes it is a mechanical fuel pump, new about 1 1/2 years old. But like I said, never had a vapor lock problem before in almost 3 years, including many 100+ degree days driving. I know there are a lot of guys with vapor lock problems and more due to gas containing ethanol, especially hot rod guys, but they have been putting that stuff in around here for a while now and if that was the problem, I would assume it should have become and issued quite a while back. That's why I'm leaning towards and asking about possible ignition module failure due to heat or being a cheap part, etc. So can an ignition module work/ fail intermittenly? Is that a sign that it's on it's way out? I guess it's possible the new one I bought could be faulty and only passed the test because it's not being tested atop a hot ass Chevy motor, but I would have thought eletrical wise, it either works or it doesn't. Period. Am I wrong with thinking that about an ignition module? Due to heat? Thanks for the reply guys, the real world answers and experience help a lot.

 

[Elbert]

While I have two vehicles with 350 SBC now.... I've not checked a module in years...(back in my hot-rod days)...anyway... as I recall there was not a good test for HEI modules that was postive for failure or not. Its important to use the grease that comes with the module. You can also have a coil fail.

You can have random issues due to heat, in relation to the coil and module. Generally I use NAPA products and they are good. I would get a GM module and coil, both easy to replace.

Like I said..... years ago you could not trust the module test.... I've replaced modules that tested good where the vehicle would not start and the new module fixed the problem.

I don't know what kind of carb you are running, quadrajet or holley (or holley offroad carb). Vapor lock can be a pain in the but to solve. As I recall the solution there was to run a electric fuel pump, which seemed to help, and obviously route fuel lines away from heat and reduce underhood temps where possible. I for one don't like rubber fuel hose around the engine. THe OEM setup seems to work very well for a quadrajet... hard line from fuel pump to carb. I think the rubber hose introduces heat issues as well as saftey issues. I know the OEM toyota fuel lines were insulated so that may be a clue...

Next time it dies.....see if you have spark at the plug wire when cranking. Doe the truck just simply cut off? Or does it kind of slowly die...and loose power?

You can also try an insulator / spacer between the carb and the manifold, or one of the heatshield type plates they make. Whatever it takes to reduce the heat impact to the carb and fuel line.

 

[FJKai]

That helps at least in regard to the "testing" of the module and the reliability of it. I'm running a quadrajet carb, and when it dies it just cuts out period, nothing. No loss of power type symptoms, hesitation, etc., it just flat out dies like "the power plug has been pulled." When it first happened, I actually thought that the ignition module had went out again, but then it fired up shortly afterward. It's done this a few times now, and now I know if I let it cool it will start and run again. I hope it's just a faulty module, that would be easy. Btw, when the original module died, I changed the cap, rotor, and coil until I was made "hip" to checking the module, so most everything in the dizzy is new. Thanks again for the advice and help.

 

[chesshircat]

Dude... I'm having the exact same problem in a 40. Changed the whole fuel system, lines and electric pump. Rebuilt carb. Plugs, wires. finally gave up, its been in the barn for 3 years. Let me know if you figure it out. It used to be just occasionally, now its every time i drive it. Like someone shut the fuel off or pulled the coil wire

 

[Elbert]

don't know if this is the issue... Are you guys powering the HEI distributor off the coil wire of the toyota wiring harness? Read somewhere that you need a relay and heavier guage wire, as the HEI distributor draws more amps. (don't know how accurate this is).

It sounds like a wiring problem as I don't recall vapor lock acting like the engine just shuts off dead cold.

First things first.... I would want to know if I had spark at the plug wires when this happened when you try to crank it.

Got to know if its fuel or spark issue?

 

[FJKai]

Well I don't know on the coil wire issue (I'll look, but it's probably like you stated), but I do know that the way it's wired is how it's been done many a times by a local cruiser mechanic here, and the other conversions he's done all run fine. Like I said, this has been running fine for almost 3 years, but as I've said before, this all started after the ignition module died about 2 months back (so I'm leaning towards this area first). I put in a different one today, didn't have a chance to run it yet, will do so tomorrow. But since now it's in the 80's and not 100+ I'm sure it will run fine. I'll try to pull a hill and see if I can get it hot enough to fail or vapor lock (?). If I do, I'll be sure to pull the wire and see what it does. I'm sure the wife is going to be thrilled to hear we're going for a drive to actually try to make the cruiser die on purpose.

Chesshircat: That's exactly why I'm trying the boards first, I don't want to rip everything apart and "re-do" the fuel system if it isn't really the problem. Mine definitely just cuts out and dies. Sometimes it will even fire back up right away, but only for a few seconds and then dies again. At that point I know what's coming so I just pop the hood and sit and wait till it cools down a bit and then it will start up and run again. I can't get a for sure answer on the ignition module "intermittent failure" due to heat. I've done a lot of research on the net and it's about 50/50. Some guys claim yes, even have the same symptoms, and just as many guys say no it doesn't work that way. Hell, I've even asked mechanics and it still is a 50/50 split. All I know is that's when this all started. Some guys even claim "today's" electronics parts all suck because they are made over seas and they are cheap and that's why they fail/ or start to with high heat. They even say to go to the junk yard and find an old stock chevy dizzy and pull it just to get the "good" old skool American made module to solve the problem. Seems kind of extreme to me, but if I had your [Chesshircat's] problem for 3 years, damn, I guess I'd be in extreme mode and try it. I'm just hoping I don't have to go that far. I've even thought about trying to wire up some type of fan to blow on the dizzy (not sure what, computer fans?? Or??) but I don't know if that's truely the problem to go that crazy yet. Hell, maybe fans all over in there, carb, fuel pump, dizzy? Seems crazy, but I'm starting to go crazy over this myself. I'll see how it goes tomorrow I guess.

 

[chesshircat]

Mine doesn't do it when its hot only. It used to do it after it was run a while, now its all the time. If I take my foot out of it, it will correct itself. If i keep my foot in it, it will quit all together. When i make it shut off completely, the fuel filters are full, fuel lines are full and the squirters in the carb squirt fuel, and the plugs have fire, it will fire right back up.

FJKai, I'm not in extreme mode, I'm in f#$K it mode, its been parked for 3 years. Every now and then i'll take it out for a spin, b/c maybe the cruiser gods fixed it, but no luck

 

[FJKai]

LOL! I understand the F#$k it mode all too well myself. Your symptoms are different than mine though. Mine's definitely a heat issue somewhere...... affecting ..........something. Based upon what you've done and what you say it does, I'd be in F- it mode too.

 

[ntsqd]

don't know if this is the issue... Are you guys powering the HEI distributor off the coil wire of the toyota wiring harness? Read somewhere that you need a relay and heavier guage wire, as the HEI distributor draws more amps. (don't know how accurate this is).

It sounds like a wiring problem as I don't recall vapor lock acting like the engine just shuts off dead cold.

First things first.... I would want to know if I had spark at the plug wires when this happened when you try to crank it.

Got to know if its fuel or spark issue?

HEI's are power hogs. The OE power supply wire is either a 12 or a 10 gauge wire. Using the original Toyota ignition wire to drive a relay switching a large gauge power wire right off the battery is an Excellent idea. I'd do that regardless of where the problem turns out to be. Consider a breaker or something in the wire at the battery just in case.

I can't imagine how a vapor lock problem would be such a sudden stop. There is fuel in the fuel bowl, that means that it should shudder to a stop ala typical vapor lock. Only with EFI can I think of a situation where loss of fuel could be an instant shut-down. It's possible that it is fuel, but I'd make certain that the ignition is behaving absolutely without fault first.

I had that instant shut-down happen to me once in my '79 Suburban. Bombing down the road into El Arco, Baja and suddenly nothing! Turned out that the power feed wire terminal had lost it's retaining clip and had vibrated off. Hooking it back up restored engine function. 37 T&B zip-ties insured that it would not vibrate off again.

As has been noted, the Heat Sink grease is crucial to the survival of the module, but it sounds like that's been well taken care of.
A note about modules, years ago MISF & I did a test on two different modules. His '69 Pontiac Le Mans had a Davis Dyna-Mod module in it. His mom's car was a mid-ish 80's Hurst Olds with an OE module in it. We did a dwell vs. RPM test on both of them.
Both idled at 45* dwell, but the OE module rapidly lost dwell angle as the RPM increased. Was down to around 25*-30* as high as we dared free-wheel that engine (been several years since that test, memory fades....). The Davis module in the Pontiac had 45* as high as we dared go with the Pontiac's engine. I am pretty sure that this is why the HEI has a rep for falling on it's face btwn 4500 and 5000 rpms. I've been in that Pontiac at a 5000 rpm shift to second (with a 2.79 axle ratio & ~26" tall tires that's really moving......... ). We could feel the cam running out of omph, but the ignition was still strong.

A possible option would be to go to one of the aftermarket ignition boxes. I would highly suggest a Marine version if you do. I'm biased towards Crane, but both Crane & MSD boxes can be driven directly by the magnetic pick-up in the distributor (eliminating the stock module). Both also offer a kit to move the coil out of the cap as well. The advantage to both of these options is heat rejection; though I'm not convinced that the aftermarket parts are as reliable as OE quality stock parts (MTBF). Still, those two names both have good reputations. MISF eventually replaced the Davis module with an MSD system in a search for more power. He didn't find much there.

 

[Elbert]

just a note on stock GM HEI...at least one from a 78 Z/28. Some years ago back when speed and power meant more than reliable transportation... I had little hot-rod z/28. Semi built strong 350... would pull 6500 RPM all the time with stock HEI distirbutor, right around 6500 it hit a flat spot. I never tried to push it beyond that since the engine was not built to see RPM higher than that. So anyway they will perform fine to 6500 RPM...I've seen that first hand many times Anything you do to help the spark I'm sure would be a plus...but I don't think its running out of power on a stock engine, espically something that does not see above 5500RPM (given that it has sufficient / appropriate ) wiring to feed the HEI distributor.

You've got to narrow it down between fuel and spark. If you're saying the truck cuts off dead cold, then I don't think that's vapor lock.

 

[ntsqd]

If the power supply wire is smaller than a 12 gauge, it probably doesn't have enough current capacity for peak spark demands (starting, high rpm, etc.). It may continue to run during those times, but that doesn't mean that it is running as well as it could be.

Since the on-set of the problems began with the changing of an ignition part, I would be inclined to make sure that everything about the ignition system is performing to it's best ability. Only after that would I start to look at the fuel system. The symptoms do not sound like fuel to me. Doesn't mean it isn't, just that it doesn't sound like it is. As a friend of mine was fond of saying, "Do something, even if it's wrong you're at least moving forwards."

 

[lehiguy]

I'll bet the farm you have an ignition module issue or a coil issue (grounding or arcing). A cracked cap will sometimes act like this as well. As cheap and as plentiful as HEI distributors are, just pick up a spare at a wrecking yard. Or you could get an MSD which essentially replaces the ignition module. If you get something new, I think it's best to get a distributor with an external coil; less heat buildup and problems will be easier to locate. For the record, I have used the Toyota power source for my HEI for six years and I have never had any ignition issues in 100k miles.

 

[FJKai]

I'm going with the ignition module getting too hot and being a crappy one (*cough,Napa, cough, cough). I put in a cheap $18 Autozone one (Duralast brand?) and it ran fine. I drove it up and down a local hill with the a/c on and was able to get it up to 240+ degrees. I even pulled over at the top once and let it sit and idle for a while and it just kept on running. That temp range was well within where it was dying and cutting out at. I agree with you Lehiguy, I'm leaning towards an eventual "different" ignition type, for sure if this module starts to give me issues. Not to really knock Napa, could be just my typical bad luck that I bought a new module that was faulty to begin with (apparently testing it isn't the most reliable thing either I hear), I'm not totally sold on the "Duralast" one, but hey, it works at a higher temp. so far. I'll probably just buy an OEM GM module (I think it's the same price as the Napa anyway) and keep it in the glove box for a switch out if this newer one starts to fail in the future. Thanks for all the input, I appreciate it, it helped to at least ease my mind a bit. We'll see what happens in the future.

 

[lehiguy]

I'm going with the ignition module getting too hot and being a ****py one (*cough,Napa, cough, cough). I put in a cheap $18 Autozone one (Duralast brand?) and it ran fine. I drove it up and down a local hill with the a/c on and was able to get it up to 240+ degrees. I even pulled over at the top once and let it sit and idle for a while and it just kept on running. That temp range was well within where it was dying and cutting out at. I agree with you Lehiguy, I'm leaning towards an eventual "different" ignition type, for sure if this module starts to give me issues. Not to really knock Napa, could be just my typical bad luck that I bought a new module that was faulty to begin with (apparently testing it isn't the most reliable thing either I hear), I'm not totally sold on the "Duralast" one, but hey, it works at a higher temp. so far. I'll probably just buy an OEM GM module (I think it's the same price as the Napa anyway) and keep it in the glove box for a switch out if this newer one starts to fail in the future. Thanks for all the input, I appreciate it, it helped to at least ease my mind a bit. We'll see what happens in the future.

Let me share my pain with you. I just installed a modified TBI system on my 350. I had purchased a brand new distributor on Fleabay for the whopping sum of $30.00 complete with cap, rotor, ignition module, the works. Well, I developed some massive oil leak after the install and it had me baffled for some time... that is untill I felt all this hot oil on the underside of my new dist. It seems the Chinese (who am I kidding? I know where this was made) haven't yet tried this thing in a real motor. The spinning shaft pulls oil up through the oiler hole and into the housing where it bathed everything in oil and was running down the back of my motor like a had drilled a hole in something. Out came the Chinese junk, in went the original GM unit that looked like it had spent several months at the bottom of a canal. After a liberal application of carb cleaner, I stuffed it in and the old girl runs like a scalded cat. Gotta love the original GM stuff; ugly as hell but still works.

 

[ntsqd]

I'll bet the farm you have an ignition module issue or a coil issue (grounding or arcing). A cracked cap will sometimes act like this as well. As cheap and as plentiful as HEI distributors are, just pick up a spare at a wrecking yard. Or you could get an MSD which essentially replaces the ignition module. If you get something new, I think it's best to get a distributor with an external coil; less heat buildup and problems will be easier to locate. For the record, I have used the Toyota power source for my HEI for six years and I have never had any ignition issues in 100k miles.

I've been thinking the same thing, poor hot module performance.

Interesting that you've had no trouble with that power source. I've done or helped on a couple HEI transplants that had to have the relay deal installed or they didn't behave right all of the time. They'd all run off the OE power, but not always did they run well. They'd miss or otherwise crap out in certain situations.

FWIW I've run a stock Toyota coil & ignitor on my air cooled VW powered dune buggy for going on 15 years. I converted a VW distributor to use the stock Toyota reluctor & pick-up coil (or was that one the Subaru pick-up & reluctor? they're very similar).
The pulse put out by the HEI's pick-up coil is a particularly strong one. With one of the "coil out of the dist. cap" conversion kits for the HEI distributor it would not surprise me in the least if the stock toyota ignition parts worked very well on a GM V8. I tend to favor OE parts over aftermarket or mass marketed replacement parts for their superior life span and robustness. Of the 5 Ford Dura-Spark II conversions that I've done (one in a IH Scout) all but one still have the OE module that I pulled off the donor in the junkyard. The one that does not have a stock module got converted after the original install to a MSD 6.