HEI Ignition Problem

[nrb's70gmc]

Hello guys i was hopping i could get a few ideas or maybe an answer to my hei problem.

i have a sb350 with a mallory hei about 8 months ago i replace the cap/rotor/module.

about a month later after that, i was driving my truck and it just died (no spark) turns out when i replaced all that stuff i pinched one of the coil wires when i screwed the dust cover on.

so i bought a new coil and put it in- everything has been fine sence.

today i was pulling out of my driveway and the truck started sputtering and cutting out. i thought it might be a moisture problem so i pulled the cap off everything is dry and the rotor looks good.

i noticed whare the carbon brush goes thought the center of the cap (underside) that the plastic was chipped- so figued that was the problem.

i got a new cap and put it on i went a round the block and its doing the same thing so i guess that wasn't the problem.

im reallllly confused now because yesterday it was runnin fine.

so what do you guys think it could be?

[72swb_327stroker_?]

pull the plugs... That could tell you more than any thing we can offer as speculative advice.

pull each plug and note what cylinder each one came from so that you can "READ" the plugs and get a better idea of whats going on with the motor.

It may or may not be an ignition problem.

1.How old is your battery? Are all the terminals, grounding points, and straps clean and corrosion free? Battery cables look good?

2.How is the carb? New? Old? Rebuilt? What type?

3.How much Gas is in the tank? Do you have a fuel pressure gauge, or regulator?

4.What type of plugs do you have and when was the last time you gapped em? Check that all the plug boots are sitting on the plugs properly, and not jumping spark from any frayed wires.

5.Do you have a back-up ignition module?(might wanna pick one up) if so swap it... if its doing the same thing, you can rule this out.

6.Are you running an external ignition box? (msd type)

7. Does it idle fine, but only misfire(sputter&cut-out) under a load or when driving? Or is it constant? Does it worsen when the motor is warm?

Answering these question can give us a better idea of what might be the problem

Cheers!
Eric

[nrb's70gmc]

Ok here it goes lol

1, battery is about 1 month old all connections are clean
2, the carb was bought new in 2002 (edelbrock)
3, the tank is full (the engine starts right up)
4, i use accel u-grove shorty plugs (bought and gapped in 2004)
5, yes i have a back up module and plan to swap/test it
6, no external ignition box
7, i just went out and was listing to it at idle (really rough/cutting out) i was revving it from the carb and it would cut out and sputter thoughout the diffrent rpm range.

like i said yesterday there were no signs of any problems--i think this is an ignition problem because i have had this happen before but i cant remember what was the cause but im really thinking it may be the module. but i dont know for sure.

[extd56]

I had the same problem with a 72 Suburban and it turned out that where the hot wire for the HEi was plugged into the fuse box was corroded and not getting a good connection. To see if that is your problem connect the hot wire from the HEI directly to the postive post of the battery and see if it runs good then.

[nrb's70gmc]

dupdate-- i switched the module and put the original one (from 2005 when i bought the hei)

to tell you the truth i dont know if the spare (origanal) was a faulty one or not i replaced the original one (stock) about mid 2009 with a new one (the one i just took out) i put the original (stock) in and went around the block

the mortor started right up idled fine i started driving (about 2 minutes after the engine was running it started sputtering and cutting out again. Damn it

i pulled back in the driveway poppped the hood and was reving the motor from the carb after a few rmp cycles the motor shut off i went and starded it again (fired right up)

during this test the motor was probally running for a good 4 minutes constaint---im so lost now as what i could be,,

can coils go bad? the one i have was bought new and is not very old.

[Slick67]

The hot wire that goes to the HEI needs to be at least a 10 gauge otherwise it may be starving for power and inturn run rough. If you are running the factory wire you need to upgrade. Make sure there are no resistors between also.

[cdowns]

have you changed your fuel filter recently?

[nrb's70gmc]

um no, i know that is a possabilty also because i have had the engine cut out from that also but that seemed to be when the engine is under a load

[nrb's70gmc]

Originally Posted by Slick67

The hot wire that goes to the HEI needs to be at least a 10 gauge otherwise it may be starving for power and inturn run rough. If you are running the factory wire you need to upgrade. Make sure there are no resistors between also.

Are you talking about the 3 wire plug that plugs into the hei?

[extd56]

I believe he is talking about the hot wire that runs into the cap on the right side that says BAT. The other side is for a tach lead.

[nrb's70gmc]

Originally Posted by extd56

I believe he is talking about the hot wire that runs into the cap on the right side that says BAT. The other side is for a tach lead.

there are a total of 4 wires going to the hei there is a plug with 3 wires and then there is a seperate wire that plugs in.

[nrb's70gmc]

i have been reading about how the (pickup coil) that connects to the module can go bad- and the function of the pickup coil can be affected by a cold/warm engine.

(when my engine warms up that seems to be when it is acting up)

[nrb's70gmc]

i have never replaced the (pickup coil) or the condincer

[Wrenchbender Ret]

There is a metal contact that goes under the coil at the coil mounting screw. It is a ground & goes to center were the 3 wire connecter plugs in. Sometimes a guy changes the cap & leaves this in the old cap. It will cause all sorts of problems 1 of which is burning the center electrod. The pickup coil can cause intermitent problems also as it moves & bends the wires when the vacuum advance moves. You have to remove the dist. & take out the shaft to replace it. The condenser is for radio suppression & not likely to cause any problems.

[cdowns]

you installed and gapped the plugs 6years ago// you sound like the "setit and fergetit" guy// great maintenance schedule , about the same for the fuel filter? howz about da airfilter?

[Jeffs70]

are you running headers? If so check to make sure all your plug wires are away from them and not grounding out on the headers or even manifold. check the boots to make sure they are good to go also. something as simple as a plug wire grounding out or jumping spark from them to your manifold or headers can be an issue.

[neba]

a couple of suggestions: old yellow wire that gave power to dist must be replaced with a new wire right from the fuse block. yellow wire is under 12 volts, not enough for hei.
make sure you put carbon center piece in cap before rubber washer, if washer is installed first will cause pole to be too short.
look under rotor. if you see a burnt mark in center replace it. spark can arc right through rotor
to check pick up coil, pull on the 2 wires. if 1 stretches its broken inside insulation.

[neba]

the 2 wires to the pickup coil bend everytime vacuum advance moves. eventually 1 breaks. usually inside the insulation.so it will conduct at an idle then fail as advance moves. by pulling on each of these wires 1 will stretch showing its broken inside. another test for this is disconnecting vacuum hose.

[nrb's70gmc]

yes i run headers all the wires are clear

i change and maintain my air/fuel filters every few months
i will need to take a look at the rotor when it stops raining

i take care of my stuff--dont get me wrong

i have never had a problem with my wires/plugs so i have never had to question them

i dont know if this helps but i only have around 15,000 on the brand new engine sence 2004 and that includes the spark plugs and wires- just for refrence all the ignition problems in the past have stemmed from the mallory hei.

guys please dont asume i lack in maintaing my truck i fix and replace things as they break or wear out. when i dont know what the problem is i ask for help.

i do appreciate all the information you have given me.

[mr48chev]

And any or all of the above mentioned things will cause the miss or rough running you are experiencing.

The heavy (10 gage) wire to the distributor from the ign on pole on the fuse block is a must. Also make sure that it is firmly connected to the "batt" pin on th cap. I am having issues with mine right now as I have an old Hei primary wire off of a doner rig that has the clip to hold it on the cab broken. Every once in a while it gets just loose enough to cause the engine to die or miss. I've gotten pretty good at pulling to the side of the road and reaching in and giving the wire a push back in place and going again.

The wires on the pickup coil that Neba mentioned bear checking if the thing has some miles on it. That exact thing was a nemesis for me on one engine running problem for a customer and it took another mechanic in the shop to bring it to my attention.

I'd change the fuel filters just as a matter of course and I put one between the tank and fuel pump on everything I have that didn't come with one there originally. On a rig that has been sitting for a number of years you can expect crud in the tank.

That carb has been sitting around for the past eight years either in the box on your shelf or sitting on the engine. That makes it eight years old which isn't exactly new. You may have low or few miles on it but it may need to be freshened up with a new kit.

Also the plugs are six years old and if you only made short runs with them or fire up and run they may need to be changed.

[nrb's70gmc]

What is the job of the pickup coil?

[72swb_327stroker_?]

honestly... a spark plug that is gapped a little off can cause symptoms like this.

this is why I run platinum plugs... You NEVER have to gap them, and they run better/colder and producer stronger spark. something to consider...my local napa has champion platinum plugs for 2.69 a piece.

[nrb's70gmc]

i need to run shorty plugs because of my headers-- if i ran regular plugs than the boot would be touching the headers.

[72swb_327stroker_?]

ahhhh... I see.

Were you able to pull the plugs yet?

[chevytrucks]

These 40 yearold tanks are hard on fuel filters. I would replace it just to get rid of the idea.
I have also had the same problem as everybody else with the hot wire. Last time it was simply loose on the fuse panel side. inspection told me it was that way for a while because everything was a little black and melted. Now I look at it all the time even with no problems. also check the motor side of your negative battery cable. I've seen easier fixes.