I have found a strange problem. Cylinders 1,2 had plugs that were much richer than the rest. We replaced the plugs and plug wires and no change. Cylinder 3 has a plug that is too clean. I will be looking to test the injector and harness next. Thanks for all the suggestions.

 

Gasoline?
Dyno calibrated and performing properly?
All wires & plugs OK?
Ignition timing where you need it?
Injector spray patterns OK?


G'luck.

 

Was this same dyno to same dyno.....that is a HUGE number if the engine seems to be running OK.

How much run in time since the rebuild?

Is there any indication of knock?

Old fuel in the tank?

Ken

 

When I was there on Thursday, and Jim said you couldn't start the car, was the speed sensor NOT hooked up, or broken and you replaced it?

When you replaced that, did you move around the injector harness as it weaves back there?

I know its difficult to get to thats stuff possibly because of that huge intake, but unless you are using totally new stuff in there, things can get iffy as you well know in those wires.

But 67HP is alot. Obvious stuff like "What does it sound like" comes up.

 

Hmmm....a short anywhere in the injector harness would prevent all the injectors from firing. They get 12V all the time and fire by the LH taking one side of the leads to ground as a single batch.

This sounds like 3 bad injectors. 2 leaking and one not opening as well as it should. It is possible 3 has a broken lead and not a short, but the other two are harder to explain by a harness problem. Also, if the injector for cylinder 3 were entirely out from a harness break you would know by seeing no change in the idle if you pulled the sparkplug lead to it.

However, would 67 HP be about the right amount for a dead hole in your car? Maybe 3 is out after all. Spark plug lead pull would confirm it. So would an injector lead pull, for that matter. I would expect an obvious miss that you could hear if you had a dead hole.

As a test, swap the injector leads on the bad cylinders for other cylinders next to them, if you want to. I'll bet the problems stays with the same cylinders.

Just go ahead and replace the injectors on the bad holes.

 

Can you post dynographs..and a/f graphs..that would help in the diagnosis..

good luck,
Tom
89GT

 

67hp?? Meh.....six hours in Tim's garage you'll find 200hp you never had

 

Something end up in the intake or exhaust when things were apart and now causing a restriction? Things like shop rags and mouse nests have ended in places like that and caused problems more than once.

 

Use your IR temp gun on the exhaust ports, looking for a colder cylinder. A too-clean plug says injector not plugged in correctly, broken wire, stuck, something. The exhaust port will be noticeably colder on that one.

 

I think we found it. The one injector was not firing. We cut open the harness and found where the wires had broken. We repaired it and hope to go to the dyno in the morning.
I'll post the results.
Thanks again for the help.

 

Good one, Larry. I had fleeting thoughts of lost rags too but thought they would have been sucked in and caused much worse problems that would have shown up in the compression tests. Fortunately, Mark has a special intake that I think can be popped open and examined easily. Actually, even with the stock intake, you could just remove the side plates and have a look inside the passages and do some probing for foreign bodies.

 

Glad you found it, Mark. That was among my list of possibilities, but the other 2 rich holes caused me to add other things. Normally a dead hole causes a regular miss, but maybe this is not so obvious is a race motor. Off to the races!

 

Good job Mark!

If your wires within the wiring harness are brittle, I would go ahead and replace the whole harness with one that's supple as that's what I eneded up doing with Ronn's car. I had several injector wires broken and shorted together which happened after I removed/installed the intake, and must have occurred when moving the harness/injectors around during the process.

The one good thing about that ordeal was that I learned how to read the workshop schematics.

The weather is looking absolutely perfect for Road America; high 60's low 70's with no rain!

 

Going back to basics you have ample compression so that only leaves spark and fuel.

Given that you have issue with 2 cylinders the likelyhood would be fuel and as Bill states an injector or 2 is probably the issue.

Given your resources I'd replace all the injectors and go from there.

 

Hey Mark, 928 Specialists could probably order you a new harness if you need one, LMAO. Sorry, you just made that too easy and I couldn't resist. Note to self: stop drinking and posting.........