Only getting spark to half of the engine. PLease help.

[Johnny-T]

So last month I was having some upgrades done to my daily driver 967. A DPI exhaust was added then we moved on to replacing my original fuel lines with braided SS lines. While in that area I had a tune up done as well. But while working on things we found my wiring harness had been cut and re-routed in several places and we were having to tape up and fix things as we went. Once everything was back together the car wouldn't start. It didn't seem to be getting any spark at all. After switching out distributor caps and plugs back and forth from the new ones and old ones we were able to get spark on the left bank but still nothing on the right bank. Obviously the car still wouldn't start so we came to the conclusion that some exposed wires on the harness had probably grounded on something possibly causing damage to the distributor.

A couple of days ago we finally got to putting in a new harness and distributor. We put in new plugs and everything but the result was the same. No spark to the right side of the engine. We tried switching out the ECU and that had no effect. The strange part was that when testing all the sparks, the 3 that weren't working would actually get a little burst of spark as the engine was turned off. We eventually messed with the mixture while cranking and got the car to start and idle. But still only on 3 cylinders. The engine actually idled pretty smoothly considering... But the car barely had enough power to get up my driveway. We then tried switching out the coil and ballast resistor but neither of those made any difference either.

Everyone is completely stumped. We have changed everything that could be causing the problem and nothing works. How can we be getting good spark on 4,5,and 6 on the left and nothing on 1,2,and 3 on the right until that last split second when the key is turned off? What are we missing? At this point we are considering putting in a new system that will bypass the ECU, coil, ect and give us a stronger spark and hope that it inadvertently fixes the problem. Has anybody ever seen or heard of anything like this before?

Any help would be great. As my daily driver, it is becoming increasingly difficult for me financially and emotionally not being able to get 967 back on the road.

[Bitsyncmaster]

That is really a strange problem. Only thing I can think of is your distributor cap is faulty since you have already replaced the distributor.

Edit: I see you already tried another cap, did that also include a new rotor?

[dmcnc]

You also changed your exhaust system. You could check the air-flow out of your new headers on the dead side. No airflow would kill all three cylinders on that side. Maybe troubleshoot with the original headers installed?

[Rich]

I think Dave picked up on the likely component.

With an odd-fire engine as in original D engines the symptom you describe is possible if the rotor/distributor and the plug wires are out of sync by one firing interval either way. Am not talking about the firing order. Long story.

Check that you did not install an even-fire distr. cap* (assuming that's even possible).
Check that the distributor is installed correctly per M:01:02 in Workshop Manual based off of TDC for #1. That is critical - assume nothing.
Check that #1 plug wire is on #1 TDC plug tower.
Check that the ign. timing is really set to #1 cylinder (rt front).

*Correct (odd-fire)cap looks like this, with the ignition towers sort of arranged in 3 pairs - looks weird but evenly-spaced towers (as used on even-fire PRV's) are bad for us:
http://store.delorean.com/images/Pro...ium/102606.JPG

[DMCMW Dave]

Did this happen before or after replacing the distributor/cap etc.?

I don't understand how anything in the harness could "damage" the distributor. It just doesn't work that way.

The only part of the system that is separate right bank /left bank is the cap and wires. The ECU has no idea what plug it's firing at any point in time, and neither does the pickup coil in the distributor. Replacing the ECU won't fix this, you already proved that by swapping it with a known good unit.

Recheck your wiring, and make sure you don't have a bad (cracked or bad center spring/button) cap and rotor. I've seen new ones bad right out of the box.

What kind of wires are you using? What kind of plugs?

Did you try swapping the ignition coil itself with a known good one? Also be sure to verify that the +/- is connected correctly and that the condenser is on the right one. Go by wire colors, not position. It makes a huge difference.

[DMC-Ron]

I am new to DeLoreans, but regardless of car type this is a strange symptom. Here are some troubleshooting suggestions:

1. Get a spare (or temporarily remove) a spark plug and spark plug wire. Connect the wire directly into the coil and secure the plug where it is grounded and you can observe it firing (dark area). Crank the engine a observe the spark. Is it irregular (skipping) or regular? you might be able to detect an erratic pulse if the issue is with the coil or distributor firing signal to the coil ( this is because the firing order is 1-6-3-5-2-4 and, as such, does not uniformly alternate from left to right engine plugs). Erratic spark would let you focus on the coil and distributor. Nice even firing spark, start looking at the distributor cap and spark plug wiring.

2. If the coil spark checks out, you can take the same test plug, plugging one by one into each cylinder connection on the distributor and observing the spark.

All the testing should be done with the distributor cap in place. Use caution when testing exposed spark plug in the engine compartment.

Ron

[David T]

The only thing that would prevent you from getting spark to one side is if you damaged the ignition wires to that side. Check the resistance of each ignition wire or just replace them. If you are getting spark to one side the distributor, coil, ECU, wiring harness, etc is all working.

[FABombjoy]

Normally I don't like to add "hail mary" hypotheses, but this one is just weird enough to throw in another consideration:

Assuming:
-Proper distributor cap
-Proper rotor phase angle
-Known good ignition ECU

The trigger wheel inside the distributor does have a built-in asymmetry that will favor one side of the block. See part #8 on the diagram here:
https://www.deloreanautoparts.com/de...t-overview.jpg

You could scope the output of the pickup and look for a clean VR signal. Maybe there is a bent pole piece, flaky impulse coil, or something like that? Do you get 6 sparks / 720 degrees off of the coil?

[Ron]

( this is because the firing order is 1-6-3-5-2-4 and, as such, does not uniformly alternate from left to right engine plugs)

I might be misunderstanding you, but just in case:
I like your thinking but with our engines it doesn't normally fire uniformly because the angle between each firing is different, while alternating from right bank to left bank ( 1-6-3-5-2-4 = R-L-R-L-R-L).

======

Johnny, you said it "didn't seem to be getting any spark". Did you check for spark actually getting to the plug wires and/or to the plugs?
I'd definitely check each position on the cap with a known good plug and wire as DMC-Ron said...

Also for, "3 that weren't working would actually get a little burst of spark as the engine was turned off", was this all 3 at the same moment? If so, that and you putting in a new distributor makes me suspect the cap/fit.

[DMC-Ron]

Ron,
You are absolutely correct, on both counts. If one side of the engine cylinders doesn't get spark, it just removes every other pulse and an irregular pulse would not be apparent visually. I had forgotten also that the spark, when fully working, is not equally spaced, hence the odd look to our distributor caps.

Thanks,
Ron