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Troubleshooting Help - GM 350 Engine Dies When at Operating Temp - No Spark

evantwheeler

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Ok, started rereading this...being a Howell, the first thing I'd ask is what cam, and did that get figured into the program? Then I'd say check the block grounds, bare metal, direct from batt.

Does it fart and pop, or just real lazy? Real lazy, timing issues. Farting and popping, timing or valves.
What timing pointer and what harmonic balancer, are they matched? I run into that all the time with things. Shoot yourself in the foot before you start.
Bought this thing in 2011 the second i had enough $$ to afford my first toy, no idea what is inside the engine. Highly unlikely anyone figured the cam into the build given the quality of the rest of the work. Truck owes me nothing, ive done Rubicon, Moab, and Johnson Valley a few times and ive done nothing to it except a new fuel pump many years back. Lots of fun and good memories for a $7k spend.

It farts and pops. So i think fuel or spark issues. The thing i dont understand is why it only does it under load. If it was valves, wouldnt it do it regardless of load? After doing some reading, im going to throw a new vacuum modulator into the trans and see if that does anything.
 

hman442

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The stumbling under load at 2800 rpm could be a fueling issue. Like Mobster mentioned, new fuel & filter (if you have 1/4 or less in the tank, I'd just fill it up with new fuel, maybe get the no alcohol super, change the filter & try. Next, maybe put your old MAP sensor back on. Are you certain the new one is the same as the Howell spec sensor ? And like asked, is the timing staying at 6 at all RPMs ? To confirm your timing mark is actually 0 (correct balancer), pull #1 spark plug, crank to ensure you're on compression stroke, you can feel that with your finger on the hole, then bring it up til your timing mark shows 0, then, stick a screwdriver in the hole, and with a ratchet on the balancer bolt, move the ratchet a bit one direction, the piston & screwdriver should start going down, then back to 0 & ratchet the other direction & the piston should go down as well. That would be top dead center.
 

hman442

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I'd wait on the vacuum modulator. Is there a Crankshaft position sensor to control the Injecters? We've got photos of two different styles of distributors above in the thread. If it's truly a stand alone HEI (big cap, wires plug into upper side of cap), after you freshen the fuel & filter & try, I'd really go buy a new, complete HEI and install it. You shouldn't be able to kill the engine by pushing on a plug wire. If it's like the second distributor picture, that could be tied into the Howell system & there likely is a Crankshaft sensor. Those often fail when warm & then come back to life after an hour or two, but still, the engine shouldn't die by pushing down on a plug wire ?
 

monkeyswrench

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Bought this thing in 2011 the second i had enough $$ to afford my first toy, no idea what is inside the engine. Highly unlikely anyone figured the cam into the build given the quality of the rest of the work. Truck owes me nothing, ive done Rubicon, Moab, and Johnson Valley a few times and ive done nothing to it except a new fuel pump many years back. Lots of fun and good memories for a $7k spend.

It farts and pops. So i think fuel or spark issues. The thing i dont understand is why it only does it under load. If it was valves, wouldnt it do it regardless of load? After doing some reading, im going to throw a new vacuum modulator into the trans and see if that does anything.
With it being TBI, does it run closed loop until running temp? I wonder if the IAC is carboned up or something? I've never had a vacuum modulator effect the engine very much.
 

evantwheeler

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I'd wait on the vacuum modulator. Is there a Crankshaft position sensor to control the Injecters? We've got photos of two different styles of distributors above in the thread. If it's truly a stand alone HEI (big cap, wires plug into upper side of cap), after you freshen the fuel & filter & try, I'd really go buy a new, complete HEI and install it. You shouldn't be able to kill the engine by pushing on a plug wire. If it's like the second distributor picture, that could be tied into the Howell system & there likely is a Crankshaft sensor. Those often fail when warm & then come back to life after an hour or two, but still, the engine shouldn't die by pushing down on a plug wire ?
No crank position sensor. Distributor is identical to this one posted earlier.

6D970199-D15E-482A-BE85-EC0F2D313C1C.png


I replaced the pickup coil last night (white and green wires come out of the pickup) and that seems to have fixed my no start issue. Also, after replacing the pickup coil i could not replicate the scenario where pushing on the cap would kill the engine.

The run like crap scenario above 2800 rpm has been present since I bought it back in 2011. I bought it without driving and had it shipped from Boise to my home in Washington state so that was on me for not doing my due diligence before purchase. Being a trail only crawler, it has never really caused an issue as I never really take it above 2000rpm anyways. This is something that is bugging me that i know is not right and want to try and fix now.

When you say complete HEI unit, are you saying the whole distributor?
 

evantwheeler

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The stumbling under load at 2800 rpm could be a fueling issue. Like Mobster mentioned, new fuel & filter (if you have 1/4 or less in the tank, I'd just fill it up with new fuel, maybe get the no alcohol super, change the filter & try. Next, maybe put your old MAP sensor back on. Are you certain the new one is the same as the Howell spec sensor ? And like asked, is the timing staying at 6 at all RPMs ? To confirm your timing mark is actually 0 (correct balancer), pull #1 spark plug, crank to ensure you're on compression stroke, you can feel that with your finger on the hole, then bring it up til your timing mark shows 0, then, stick a screwdriver in the hole, and with a ratchet on the balancer bolt, move the ratchet a bit one direction, the piston & screwdriver should start going down, then back to 0 & ratchet the other direction & the piston should go down as well. That would be top dead center.
I confirmed the 0 mark and TDC last night before re-stabbing the dist.

One consideration with fuel is the fuel pressure regulator. I havent played with that. It has a vacuum line going to it, maybe the regulator is bad? I confirmed key on engine off fuel pressure was correct a year and a half back when i started playing with this, but i havent driven around and monitored fuel pressure….

I will do the new fuel new filter and sea foam treatment. Fuel is 4-5 months old, no treatment, tank was not stored full…

I still think its something else given the problem has been present for so long. Had the same stumbling issues with new fuel and new fuel pump and new fuel filter back when i prepped it for a trip to Moab in 2014 or so.
 

evantwheeler

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With it being TBI, does it run closed loop until running temp? I wonder if the IAC is carboned up or something? I've never had a vacuum modulator effect the engine very much.
I dont know if it is going into closed loop. On my sand car i can tell by using HP tuners, but still dont have the ability to monitor this dinosaur ECM with my laptop.
 

Kachina26

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No crank position sensor. Distributor is identical to this one posted earlier.

View attachment 1196364

I replaced the pickup coil last night (white and green wires come out of the pickup) and that seems to have fixed my no start issue. Also, after replacing the pickup coil i could not replicate the scenario where pushing on the cap would kill the engine.

The run like crap scenario above 2800 rpm has been present since I bought it back in 2011. I bought it without driving and had it shipped from Boise to my home in Washington state so that was on me for not doing my due diligence before purchase. Being a trail only crawler, it has never really caused an issue as I never really take it above 2000rpm anyways. This is something that is bugging me that i know is not right and want to try and fix now.

When you say complete HEI unit, are you saying the whole distributor?
Joined the party late. We had issues with those pick up coils. Heck, the connectors would disintegrate too.
 

monkeyswrench

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I dont know if it is going into closed loop. On my sand car i can tell by using HP tuners, but still dont have the ability to monitor this dinosaur ECM with my laptop.
Unhook the ect when running at running temp...it should default to cold at the ecm. This may let you know if it's ecu based spark and fuel issues, or mechanical. Kind of isolating what effects what. Easy one to try if you're out messing with it.
 

DRYHEAT

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Do you have a small block in your other 40? Why not switch them out just to rule out an ignition problem.
 

rivermobster

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I confirmed the 0 mark and TDC last night before re-stabbing the dist.

One consideration with fuel is the fuel pressure regulator. I havent played with that. It has a vacuum line going to it, maybe the regulator is bad? I confirmed key on engine off fuel pressure was correct a year and a half back when i started playing with this, but i havent driven around and monitored fuel pressure….

I will do the new fuel new filter and sea foam treatment. Fuel is 4-5 months old, no treatment, tank was not stored full…

I still think its something else given the problem has been present for so long. Had the same stumbling issues with new fuel and new fuel pump and new fuel filter back when i prepped it for a trip to Moab in 2014 or so.

If the timing is not advancing, that is definitely the problem.

Today's fuel will go bad in a couple of weeks. 😔
 

monkeyswrench

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Today's fuel will go bad in a couple of weeks. 😔
Today's fuel sucks balls! Turns into a tequila sunrise looking mix of petroleum, ethanol and water.

Had a learning curve a couple weeks ago. Chevy square body missing on acceleration. Idled great, everything where it was supposed to be...
Bore scoped the tank, clean as could be! It was also clean enough to see the "bubble" of water running on the bottom. Drained a couple gallons of water out, and ran great again.
 

rivermobster

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Today's fuel sucks balls! Turns into a tequila sunrise looking mix of petroleum, ethanol and water.

Had a learning curve a couple weeks ago. Chevy square body missing on acceleration. Idled great, everything where it was supposed to be...
Bore scoped the tank, clean as could be! It was also clean enough to see the "bubble" of water running on the bottom. Drained a couple gallons of water out, and ran great again.

I put some pump gas in a clear gas jar. Clear as water when it went in.

Two weeks later, it was all yellow and shit. If I had left the cap off, it I'm gonna guess it would have gone bad in a few days!

Remember when we were kids and pump gas was that beautiful purple color?? 💜⛽💜
 

monkeyswrench

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I put some pump gas in a clear gas jar. Clear as water when it went in.

Two weeks later, it was all yellow and shit. If I had left the cap off, it I'm gonna guess it would have gone bad in a few days!

Remember when we were kids and pump gas was that beautiful purple color?? 💜⛽💜
Purple, not so much...the bluish tinge of LL100 was what I was able to use. My old boss raced in the 50's. In 56, OKC national event, they brought their own gas for his B/Gas roadster. Gilmore "blue green" gasoline. He said the locals had never seen anything like it.

His son still has the car, 32 roadster with a TPI in it now. Same front fenders, the rears were replaced because they'd been torched to fit the slicks. In it's day, 6 2's on a DeSoto, LaSalle trans and a quick change. Now retired and just another black roadster.
 

evantwheeler

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Unhook the ect when running at running temp...it should default to cold at the ecm. This may let you know if it's ecu based spark and fuel issues, or mechanical. Kind of isolating what effects what. Easy one to try if you're out messing with it.
Upon initial cold start this afternoon, timing would retard slightly from 8 to 4 BTDC as i increased RPM until the engine heated up to operating temp. After warming up, timing advances with an increase in RPM. I assume this means it is going into closed loop mode.

Vacuum at the throttle body is around 18.5 in hg at idle.

image.jpg


Key on engine off while pump is running, fuel pressure is 46 psi. Pump off, holds steady at 44psi. Engine on pump on, 36psi. As i rev the engine, fuel pressure goes up to 40 psi.

image.jpg
 

evantwheeler

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These HEI ignition modules, they either work or they dont, correct? If the truck runs, is there any reason to replace the one currently in the distributor? Rather not put a $35 part in that i dont need….

A2A8D7F8-BDCD-407F-B6C4-63326644DF97.jpeg
 
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