Engine missing

[ZR WON]

Hey all:

I decided to replace the original wires and injectors on my 90. Re-ported the injector housings/plenum (much more aggressive than the 1998 vintage work). Finally got around to putting the car back together this afternoon, and it is missing on 2 cylinders.

I've checked the routing of the spark plug wires (10+ times); they are correct. The injectors are new FIC versions from Jon, and installed as instructed, so I can't imagine that being an issue. Basically, those are the only two things that have been changed since the engine ran previously (and well). I will pull the wires and have someone crank the motor over to make sure all injectors are pulsing tomorrow. Any ideas as to what the issue could be?

Brian A.
90 ZR-1
12.09@118
01 Z06
not quite stock

[-=Jeff=-]

did then injectors seat okay? I had an issue with a set from Jon, he swapped them ( great guy)

you may want to check for a Leaker..

[SharkPilot]

Brian,

Have you checked your coils? Each coil fires two cylinders and when one dies those two cylinders go with it. Mine had a coil fail and it ran very badly. Pull all of your plug wires off of the plugs. Each coil fires cylinders that are opposite in the firing order. 1-6, 5-8, 4-7 & 3-2 should be the pairing. I can't remember what the resistance through the two wires and coil should be but all four pairs should be similar. If you find a pair that is way low or open... there's your problem.

There are many on here that know much more than me but checking coils is where I would start.
You could also pull one wire at a time off while the engine is idling. When you cannot detect a difference that's your dead cylinder. Then check the opposite cylinder (in the firing order) and chances are it will also be dead.

Hope all of this helps,
SharkPilot

[Paul Workman]

Brian,

Have you checked your coils? Each coil fires two cylinders and when one dies those two cylinders go with it. Mine had a coil fail and it ran very badly. Pull all of your plug wires off of the plugs. Each coil fires cylinders that are opposite in the firing order. 1-6, 5-8, 4-7 & 3-2 should be the pairing. I can't remember what the resistance through the two wires and coil should be but all four pairs should be similar. If you find a pair that is way low or open... there's your problem.

Hope all of this helps,
SharkPilot

Just a pointer I picked up from Marc H. that could save the ECM or DIS...

Pulling a plug wire w/ the engine running results in a tremendous spike in the coil's output voltage (it is a law of inductor discharge as a function of load resistance). If there is any flaw in the plug wiring or say a crack in a coil boot, the voltage spike could breach the weak spot and ground out among the wires in the DIS and ECM harness that rests next to the plug wires!

I've pulled wires on distributor motors for years, but never thought about the LT5s sensitive harness resting next to the coils and the potential for disaster. Anywayz...The trick is to put a plug in the boot and ground it out and then start the engine and see if you have spark.

And, as indicated, you could measure the resistance across the two plug wire of each coil, looking for a resistance reading out of whack in comparison with the other coils. (However, a megger is needed to test high voltage circuits which might test "normal" when using a standard DVM.)

FWIW,

P.

[ZR WON]

Thanks to all for the suggestions!

It turns out the injectors that Jon had sent to me (I bought them close to a year ago) actually stuck shut from sitting. In speaking with several authorities on the subject, this is a relatively common occurrence, as the fluid used to flow test injectors contains some paraffin wax. As time goes by, it becomes sticky and can actually prevent the injector from functioning.

I cannot express my satisfaction in the customer service Jon provided through this unfortunate situation. I was on vacation last week and had intentions of getting the car back together on Tuesday. Misc issues caused delay after delay. Sensing my frustration, Jon insisted that he next day air a replacement set of injectors so I could get the car back up and running as quickly as possible. It reminds me of one of the big differentiators in a particular companies customer service. ALL companies provide 'good' customer service when things go right. The differentiator for TRUE customer service is how a problem is handled. Jon did what he needed to to get my car running, and I will continue to use him whenever an injector need arises.

I'm happy to say the car runs fantastic. The extra porting can really be felt above 5500. Unfortunately, another small problem has arisen, which I will be posting in another thread. Thanks again!

Brian A.
90 ZR-1
12.09@118
01 Z06
not quite stock

[secondchance]

Thanks to all for the suggestions!

It turns out the injectors that Jon had sent to me (I bought them close to a year ago) actually stuck shut from sitting. In speaking with several authorities on the subject, this is a relatively common occurrence, as the fluid used to flow test injectors contains some paraffin wax. As time goes by, it becomes sticky and can actually prevent the injector from functioning.

I cannot express my satisfaction in the customer service Jon provided through this unfortunate situation. I was on vacation last week and had intentions of getting the car back together on Tuesday. Misc issues caused delays after delay. Sensing my frustration, Jon insisted that he next day air a replacement set of injectors so I could get the car back up and running as quickly as possible. It reminds me of one of differentiators in a particular companies customer service. ALL companies provide 'good' customer service when things go right. The differentiator for TRUE customer service is how a problem is handled. Jon did what he needed to to get my car running, and I will continue to use him whenever an injector need arises.

I'm happy to say the car runs fantastic. The extra porting can really be felt above 5500. Unfortunately, another small problem has arisen, which I will be posting in another thread. Thanks again!

Brian A.
90 ZR-1
12.09@118
01 Z06
not quite stock

:thumbsup: