91 Z28 with 87 TPI cranks, has some spark and fuel, no start
 

Hey All,

I have a 91 Z28 that I dropped my 87 IROC 350 TPI(including engine harness)into. Basically it is an 87 MAF setup complete with MAF ECM in a 91 Z28 body and VATS is out of the picture.

Beyond the wiring which John in RI is helping me with(I think it is in a good place for it to actually fire), I re-pinned the connections to mate as properly as I can discern, I am having a no start condition.

I think my distributor may be 100+ degrees out as I get some backfire out of the throttle body, which I will rectify tomorrow. I had to pull the new distributor I bought and replace it with my old one to fix a no spark condition, it seems the new distributor bit the dust as I got spark back when I swapped to the old distributor.

I am looking for suggestions on the no start condition. It could just be timing is out of course. But even when the "new" distributor was initially put in and working properly, with close timing I got a no start condition.

I have +12v at the coil before I crank(tested with two known good coils and ICMs), while cranking it's dropping to ~+10v. Spark in a tester is orange at the coil and at the plug. I believe it should be blue or white. I have tried with the ECM spark advance plugged and unplugged.

Starter is 6+ years old and off the 87 which was my donor, I can swap it out if it is a good suspect of the voltage drop.

Car cranks strong, and quickens for a bit as if it were catching than slows down, it repeats this a bit, but in the end I am left with a no start condition.

To recap, known good coils(one is brand new) have been used, new ICM and known good ICM, swapped ECMs and proms as I have 2. Verified injector pulsing. Tested with the ECM spark advance plugged and unplugges. I have orange spark at the coil to the distributor and at the plugs as seen in a spark tester. 50PSI fuel pressure after prime and during cranking. Car will quicken during cranking but not fire up.

This build has a lot of variables I know, I am just hoping for some hints. I have been scouring the forums off and on all day and found nothing that may lead to a solution.

Thanks for any responses and suggestions.

Re: 91 Z28 with 87 TPI cranks, has some spark and fuel, no start
 

The only thing I can think of is if the distributor is 180 degrees out.
You can put a timing light on number 1 cylinder and have someone crank it over and watch the timing. Too advanced it will bog during cranking.

Re: 91 Z28 with 87 TPI cranks, has some spark and fuel, no start
 

Hmm that's a good idea. I didn't think timing while cranking was a great idea, but hey if I am unsure of the timing that is the best way to find it. I will get a light tomorrow before I start and take a look.

Thanks.

Re: 91 Z28 with 87 TPI cranks, has some spark and fuel, no start
 

Hope it’s that simple , don’t forget to check umyour firing order 1-8-4-3-6-5-7-2

Re: 91 Z28 with 87 TPI cranks, has some spark and fuel, no start
 

Aye as do I.

I will check the order again.

Thanks.

Re: 91 Z28 with 87 TPI cranks, has some spark and fuel, no start
 

Just an update. Re-positioned the distributor and I'm getting something more. It sputters out of the exhaust, so it is firing and igniting, just won't start. Any thoughts?

Re: 91 Z28 with 87 TPI cranks, has some spark and fuel, no start
 

It could be flooded. Try holding your foot to the floor and see if it clears out.

Re: 91 Z28 with 87 TPI cranks, has some spark and fuel, no start
 

Was was trying that and it didn't result in anything so I tested the throttle position sensor and I seem to have 12 voltsI through all three pins. I think it's bad.

Re: 91 Z28 with 87 TPI cranks, has some spark and fuel, no start
 

Yeh that’s not good. The 5v ref is a grey wire at c14 of your 165 ecm.
I hope the ecm isn’t damaged. The black is a ground I’m wondering if the 12v fried the tps.
I’m surprised you even had injector pulse with ecm feedback of 12v.

Re: 91 Z28 with 87 TPI cranks, has some spark and fuel, no start
 

Looks like the problem ended up being that the valve train is screwed up. The shop that I paid to put the new camshaft in did something that's causing issues. I've gone through two sets of push rods all Bend during cranking after after being tightened down to zero lash what tge pushrod still able to spin. I'm kinda at my wit's end with them but I will give them another chance to fix it.