Found my problem

[Bad Ass Black Trucks]

After quite a bit of fussing, fixing and general problem solving several issues I think I found the root cause of many of my problems. I thought I would share in case someone else has the same problem.

I was having several issues but kept coming back to ignition. I was getting spark but my AFR's were not steady at idle and it got progressively richer with increased RPM. When changing things around chasing problems I was having a difficult time setting the timing. Seemed like my timing light was messing up and I did indeed have a problem with it. The positive connection to the battery came loose and I was left with a bare wire. Fixed that but noticed that spark on cyl #1 didn't seem consistent. I thought that perhaps the inductor got too hot so I shut it down and let the truck cool. Tried again later and still had the same problem. I decided to put the inductor around cyl #3 and found the timing light was working perfectly and spark was consistent.

I finally got the timing set right on #1 and a short drive revealed a complete lack of power, rich condition and and rough operation. Going back through the ignition again I found that the pigtail from the main harness to the distributor was pulled too tight. I had turned the distributor pretty far when setting the timing and the flat spot on the dizzy was essentially facing the driver's side. I removed the tape on the pigtail and there was a kink in the wires. I re-taped and re-set the distributor gear on the camshaft and it fired right up and purred like a kitten. Got the timing light out and spark was consistent on #1. I had to rotate the dizzy to get it to 0 degrees and it wound up pulling on the pigtail too much. Spark went away and the engine stumbled until I took the stain off the pigtail. Bingo! (I think)

I re-set the distributor gear again since I didn't get it far enough the previous time. Unfortunately, I suck at getting it close to 0 degrees on the drop in and haven't had time to get it started again. I have high hopes that it will run much better now. Although, I know that I will probably need to cut the pigtail and do some soldering to fully remedy the problem.

 

[Damian]

Re: Found my problem

I'll have to look at mine then. My afrs are anywhere from 14.9-15.7 at idle. I won't be able to verify it fixes my problem until I get my crank work done.

 

[Windedv6]

Re: Found my problem

You need to reclock your distribtor. If uyou have to turn it that far you are off a tooth or two.

 

[Don W.]

Re: Found my problem

Good catch. Might be interesting to find out why, exactly, does pulling on that set of wires cause the problem. Is the issue at the dist plug or something in the harness or ???

 

[Bad Ass Black Trucks]

Re: Found my problem

You need to reclock your distribtor. If uyou have to turn it that far you are off a tooth or two.

That's what I did here:

I re-taped and re-set the distributor gear on the camshaft and it fired right up and purred like a kitten.

But I think I only got it moved one tooth. That allowed me to really see the problem. The strain was taken off until I had to rotate it clockwise to locate 0 degrees. Rotating clockwise put the strain on the wires and bam the stumble came back and the truck wanted to die. Then rotating counterclockwise, away from 0 degrees, made it run better.

I re-clocked it again and moved it about 2 teeth.

 

[Bad Ass Black Trucks]

Re: Found my problem

Good catch. Might be interesting to find out why, exactly, does pulling on that set of wires cause the problem. Is the issue at the dist plug or something in the harness or ???

I think it is the wires in the harnes right by the plug. There is a visible kink and the behavior leads me to belive the wires might be damaged inside. Although, I guess it could be losing contact at the plug from the strain.

 

[Don W.]

Re: Found my problem

I think it is the wires in the harnes right by the plug. There is a visible kink and the behavior leads me to belive the wires might be damaged inside. Although, I guess it could be losing contact at the plug from the strain.

Ya, thanks. Wiring can be a nightmare. But it's always nice to be able to actually find the problem. There's not quite enough slack in that harness. I had a similar issue (ran OK just a lot of strain on the wire) with the plug that connects to the MAP sensor. Did basically the same as you opening up the main harness a bit. Worked good.

 

[Don W.]

Re: Found my problem

How to set a distributor with the engine not running. This assumes that you are not 180º out. (If you aren't certain, then you have to pull #1 plug, establish it's on compression, and line up the timing marks).

• Loosen hold down bolt enough to turn distributor body fairly easily.
• Align the timing marks for TDC. It will be on either #1, or #4. For this static check, it doesn't matter which cyl it's on.
• If not certain where rotor is, remove dist cap and visually check that rotor is pointing to either #1 or #4.
• Turn key on, but do not start.
• rotate dist body CW, until 'points' are past the rotor points.
• Turn body CCW 'sharply'. When 'points' line up, the coil will spark, and fuel pump will prime.
• Do this several times, and get a 'feel' for where the spark/pump event occurs. Leave dist body in that position.
• Tighten bolt enough that oil pump won't make it turn.
• Start engine, and check final timing with a light.

With practice, it is possible to get the timing set within a degree or two using this method. Which is a useful skill when installing distributors.

Fascinating. I had not heard that in years. I used to do that all the time with the old breaker point style dist. Worked very well. Didn't know it worked with our dist. I've just lined up the reluctor wheel with the pickup. Gets me close enough to fire the truck but that's about it. I'll try your system next time!

 

[Bad Ass Black Trucks]

Re: Found my problem

How to set a distributor with the engine not running. This assumes that you are not 180º out. (If you aren't certain, then you have to pull #1 plug, establish it's on compression, and line up the timing marks).

• Loosen hold down bolt enough to turn distributor body fairly easily.
• Align the timing marks for TDC. It will be on either #1, or #4. For this static check, it doesn't matter which cyl it's on.
• If not certain where rotor is, remove dist cap and visually check that rotor is pointing to either #1 or #4.
• Turn key on, but do not start.
• rotate dist body CW, until 'points' are past the rotor points.
• Turn body CCW 'sharply'. When 'points' line up, the coil will spark, and fuel pump will prime.
• Do this several times, and get a 'feel' for where the spark/pump event occurs. Leave dist body in that position.
• Tighten bolt enough that oil pump won't make it turn.
• Start engine, and check final timing with a light.

With practice, it is possible to get the timing set within a degree or two using this method. Which is a useful skill when installing distributors.

Kudos to DAVE! The little trick worked like a charm. You do have to 'flick' the distributor CCW quickly. This is so the magnetic pickup can 'see' the movement and send the signal to spark. This is also why you have to do it several times, it is hard to tell exactly where the spark occured because you have to zip by it. Just rotate quickly and narrow down exactly where you had the spark, move it back to where you heard the arc and then you should be close enough to get it to fire. I was within about 4 degrees. A spark checking tool is also helpful, you can see if you are actually getting spark at the plug you think you are (#1 in this case).

My problem is definitely the wiring. I'll be digging into that soon. Anybody know the location of the pins for the distributor at the ECM? I might hook up the long leads on my DMM and check each wire the for quality continuity rather than dice up all the wires looking for the culprit.

 

[Don W.]

Re: Found my problem

Black 32 pin connector, kinda in the middle of the connector look for C8 C9 D8 D9. D9 should see ground. The numbers and letters are hard to find/read but they're there.

 

[Bad Ass Black Trucks]

Re: Found my problem

I relived some of the stress on the harness checked continuity between the wires to the ICM from the ECU. Everything checked out fine. It made me wonder if I am chasing the wrong thing. I did find a vacuum leak at the TB gasket while doing more troubleshooting with the darn truck and that helped the hunting AFR. I thought perhaps my problem was the vacuum leak all along but I now have intermitten backfiring. I took it on a very short drive at 10 MPH and there is just a complete lack of power. Runs like crap. It feels like an ignition problem and leads me back to the wires between the ECU and the ICM.

It doesn't stumble or die when wiggling the pigtail but when I put a timing light to #1 plug wire and hold the light on continuously I notice the spark is not 100% continuous. It seems to drop more spark when I move the wires in the pigtail to the ICM but I cannot hear the engine stumble or change idle speed. The backfires seem to increase in frequency when I fiddle with the pigtail but again, it's hard to tell. I really have to jerk the wires around to see difinitvely see the spark drop out and it is not consistent on which way I pull the harness.

I am starting to get confused but here is my theory: The AFR's are good on the wideband as a whole, but when I lose spark that specific cylinder is rich and dumps raw fuel in the exhaust stream. I can see that in the log. That is what is causing the backfire. I don't think the ignition problem is specific to a cylinder so the backfiring is not consistent.

I would try repair the pigtail to the ICM but I think the damage is very close to the plug and there may not be enough wire to make a good solder connection. I don't think that pigtail can be disassembled. If that is true there isn't a way to replace pins and fix it that way. Can I buy that pigtail anywhere?

I might also pick up a reman dizzy from Advance to try out if these problems persist. I wonder if the ICM got damaged in this mess or if the e-bay 'billet' distributor I am using has a bad pickup.

 

[Bad Ass Black Trucks]

Re: Found my problem

Can I buy that pigtail anywhere?

Stop looking, I think I found it: http://www.rockauto.com/catalog/moreinfo.php?pk=1217555

 

[Bad Ass Black Trucks]

Re: Found my problem

I decided to double check the plugs and see if I could get an idea of what is going on. #6 was fouled and a resistance measurement revealed the connection between the conductor and plug connector was bad. I had a spare and threw a new set of plugs in. Backfiring now stopped. Idles great and throttle response is awesome! Although, it does go way rich when reving but not as bad when leaning into it. Also getting tons of knock. I need some fresh 93 and see if it is real knock or false.