BIG No start problem, please help

[8upZR1]

I am new to this site and Zr1's in general but have a serious sittuation and I thought maybe somebody could help me out. My ZR1 is a 1990 with just under 20,000 miles. The head gasket blew from using purple ice and so I replaced it. While motor was apart I ported the heads, intake, TB. air horn, and headers. I put the motor back together and set cams at 107.5 intake, 109 exhaust. Now the motor will not start. The starter will turn the motor, the plugs are firing in correct order, and the injectors seem to work. When checked, the plugs are wet with fuel, and there is a puddle of fuel under the open headers. I have tried different chips GM and aftermarket, fuel pressure looks perfect, no trouble codes, good compression, good intake vacuum, yet no start. Every once in a while I get a pop and a fireball from the headers but that is it. Does anybody have any ideas about this situation? I am desperate because I have tried every trick in my arsenal. PLEASE SOMEBODY HELP ME OUT.

[tomtom72]

I'd be stupid if I said I knew what was wrong. The crank & cam sensors are okay? the brain box for the inigition, the one on the underside of the plenum, is okay and the other one over by the A/C box? Sounds to me like it can't find the cylinder the system uses to start the ignition sequence, cyl #6 or is it cyl #1. See I told you I don't know much, sorry.

Maybe a call to Gordon Killabrew, foryourcar.com, or maybe call Mr. Haibeck at ZR1Specialist.com. Sorry that's all I can come up with. One of the more experienced guys would have more useful input to share with you...when they see this they'll post up.


Tom

[ZR1 MK]

I assume its an ignition issue based on your description. Wet plugs means they arent firing at all or spark is too weak. Check spark at each plug to determine if you have no spark or weak spark and diagnosis according to the manual.

[8upZR1]

the cam and crank sensors are new, so is the ignition module under the plenum. coils are msd and I run the MSD dis-4+ box. I have visually verified that all plugs are firing. There is no adjusting timing so I cant imagine it being that far off. is there any way my cam timing is so aggressive that it wont start? would the plugs perhaps be firing in the improper order if I switched the wiring harness connections that go into the ignition module under the plenum? Can't imagine i did something like but then again I cant figure anything else out. Does anyone know of a way to adjust fuel mixture @ start up without burning a chip?

[ZR1 MK]

If you are getting proper spark, you might be getting too much full. Check full pressure. Try full throttle for an extended period of time (flood clearing mode as outlined in the service manual).
Just because a part is new doesnt mean it is good, although most faulty parts will create a trouble code. Easy to check each part for proper connection, voltage, resistance etc.
110 degree is the max timing for the LT5. Any more wont create more power. Why so much timing? I cant see aggressive timing as cause of the problem, but Im not the expert in that area. Are you sure you timed and locked them in correctly?

[8upZR1]

Today's mission will be to replace all new sensors with the originals to see if they are faulty. The cam timing is accurate, I rechecked each cam after instllation to verify the timing. The cam timing I chose was based on recomendation by a highly respected ZR1 builder, MR. K. He told me 108/110 for good drag motor, `103.5/106 as most aggressive he has gone. I figured since my port work was a tad on the aggressive side I would go with cam timing slightly more aggressive than the recomendation. I ditched the secondary throttles/shafts as my motor is setup for topend power, I dont care much about low speed torque. COuld my lack of secondaries have anything to do with the no start situation? Is it possible to verify timing on the LT5 with a timing light?

[8upZR1]

I have checked for codes throughout the process of trying to start the engine and never a single code.

[8upZR1]

I have just ran a little test that may help in diagnosing the problem. As stated earlier the car shows no trouble codes. I thought this was strange and so I unplugged the cam sensor and tried again to start the car. Obviously it did not start, however after the attempt I rechecked the error codes and to my surprise there were none. Just 12 12 12. Should I not have a trouble code if the cam sensor is unplugged? Does this mean ECU?

Unplugging the cam sensor will not keep the car from starting. It will just not receive the sequence for corrct firing and run in batch mode instead of sequential.

Just out of curiosity, when you pulled the original crank sensor out, did you notice if you had a small shim?

[Tyler Townsley]

Do you have a service manual? Its the best place to start. Having chased a bad dis for 2 1/2 years I can understand your frustration. You need to check the crank sensor function, depending on which you have there could be too much gap. I do not remember what it should be but this is a known problem. You can put a timing light on it to see if you are in fact getting spark at #1 tdc.

My dis would give good spark at <400 rpm but start falling apart over that rpm. Finally found a dis checker that checks the whole dis system including the cam and crank signals. The tester allows you to simulate the crank and cam signals through crank and running. I put a scope on the crank signal and cam signal and they were the the same as what was being simulated. I then ran the simulation through the dis and you could see the spark fall apart on a scope and at the pulgs.

It is called an ISS (Ignition system simulator), made by OTC model # 3575. I bought mine off ebay for $130 and it should be a tester everyone doing LT5 troubleshooting should have. It can also be used to check injectors and coil/wire problems. IE put a plug in each wire, lay them on the plenum and watch the spark across the tip. Any plug with weak spark would indicate bad coil or wire. Again easy to check, replace wire or coil and run the check again.

Tyler