Curt Baclawski

Hello, thanks in advance for any advice:

I have a 1990 zr-1 that developed a marked "stumble" when under strain(low power, vibrations, lower exhaust note). It seemed to start after a potentially bad tank of gas, but I cant be 100% sure of the timing since I rarely drive the car.

I drained the suspect gas, and ran good gas along with injector cleaner, then more with seafoam, no change

At first there was a rough idle, I changed the plugs, and that fixed the idle, but it still performed poorly under strain.

I changed the fuel filter - no change
Tested exhaust pressure and changed 02's... normal reading, no change with new sensors.

checked fuel pressure - looked good.

Now today I got brave and removed the plenum, changed the coils and injectors... AND... now it won't start at all.

engine cranks, fuel pressure is good. I removed a plug and it was wet and smelled of gas, so I think fuel is getting in. I don't think I have any spark, with a plug removed but connected, I couldn't get it to arc.

What could I have screwed up that might cause this, obviously i'm no mechanic, but trying to learn, and would love to avoid a trip to the shop and the 4 month cat and mouse game that general follows...

Advice??

mike100

It is pretty common to goof the connection to the back of the DIS plug on the module- get out your 1/4" socket, take it off and look for the bent over pin. If it is bent, carefully straighten it and reassemble. I take the map sensor bracket off to make enough room for your hand.

Curt Baclawski

Thanks!

I will try that tomorrow. A definite possibility, as I struggled mightily to get that re-connected...

RICHARD TILL

What Mike said. The same happened to me.

LT5corsa

Mike

Great advice! I was going to say just that.....

If the pins are straight, lift up the plenum and ensure the electrical connections are "in" (in front of the ignition module).



David

Dynomite

Yes.......just ran into same identical issue with a guy near San Diego , CA.

It is not a no start..... it is a no spark. He removed the plenum and when reinstalled pushed a pin socket back into the 14 pin connector (the connector with 1/4 inch bolt that connects to rear of DIS). He thinks he fixed that but still no spark. I doubt he damaged the DIS since no pin was bent and no shorting of any pins. I suggested he remove plenum and check DIS connector and coil connectors one more time.

He also mentioned the other connectors for coils and DIS had some broken locks which also could result in disconnection when te-installing plenum.

Curt Baclawski

Thanks everyone again, I'm at work, but will check the pins when I get home.


Dumb question, what is the DIS connector?

Dynomite

Distributorless Ignition System attached to bottom of plenum. The main 14 pin connector is attached to rear of DIS having 1/4 inch head bolt securing the DIS. There are actually 8 pins used in 14 pin connector.

Curt Baclawski

Are you guys able to access this connector without removing the plenum? I just spent an hour trying to do so, managed to get the bolt loosened, but don't see how I can get the connector undone(which is wired with the smaller on next to it, so I'd have to get both) without breaking something. Even if I could, don't see how I could get them back in...

Am I missing something, or to I just need to bite the bullet and ondo it again?

FASTAZU

Sorry but its best to remove the plenum

Curt Baclawski

I was afraid of that... Guess I was just hoping for a magic trick!

Dynomite

I have always removed the Plenum but I have TB Coolant Blocked at Injector Housing so removing the Plenum can be done in just a few minutes. I am thinking Mike removes the DIS connector prolly without removing the plenum as he suggested....... take the map sensor bracket off to make enough room for your hand.

I have Lee's MAP Sensor Cover pointed out as shown at rear of Plenum. There are two bolts holding the MAP Sensor Bracket to rear of Plenum. A Vacuum Line and an electrical connection are also attached to the MAP Sensor.

Curt Baclawski

I'm guessing mike has smaller, more skilled hands than I do... I removed the map sensor bracket, but still couldn't get to it... going to remove it Friday when I have some time and daylight.

thanks for all the help, I'll post my results!

DRM500RUBYZR-1

Good luck!

Why not have your phone or camera handy, and take a picture of the DIS connection right as you separate it.
Hopefully it will simply be that one of the pins was indeed inadvertently bent when re-assembled.

Such a picture might help others avoid making the same mistake.

Marty

mike100

I would try to recruit somebody who can reach behind the plenum before you take it off again. Mainly, for me, it is about getting a small 1/4 drive ratchet with just the right socket and extension length to place the tool were you can twist it. I thread it in by hand for a couple of threads on a deep 1/4 drive socket, then add the ratchet as it tightens.

You may find it easier to jack the car up, remove the wheel and put a towel over the dirty brake rotor assembly...then you can stand real close to the work without laying across the car.

Z51JEFF

The only issue I see in removing the plug with the plenum in place is its a pain in the *** to get this plugged in with the plenum loose,now trying to get it back in and fighting with no space just adds to the grief.

Curt Baclawski

Thanks all for the advice.

I removed the plenum, and checked the Distributor plug. Everything looked good there, but I'm not the first owner of this car and I could see where someone else had previously had the exact problem everyone described - the plastic connector was clearly cracked beneath one of the pins, obviously caused by a bent pin at some point.

Turns out, my connector was plugged properly on that end, but the other end down by the coils had the plastic clip broken off and I must have unwittingly knocked it out when replacing the coils.

Also, when inspecting the vacuum line that connects to the MAP sensor I noticed it was clogged with some really sticky, almost tar-like substance. I have no idea what it was or how it got there. So I replaced that too.

Once done, The car started right up and ran great. I don't know whether it was the coils, injectors, or the plugged sensor hose that was the root of the problem, but I guess it doesn't really matter...

Only thing left for me to do at this point is to verify that the secondaries are opening properly. The engine feels strong, the vacuum pump in the front on the passenger side cycles normally, and I really have no real reason to suspect they are not, but I still want to check to be 100% certain.

I know I probably should have addressed this with the plenum removed, but I really couldn't see past just getting it running again.

Any tips on the easiest way to do this would be great!

Thanks again,

Curt

ghlkal

Good work, and thanks for following up with the solution.

I'm not sure how to tell visually with the plenum on, but you can tell if the entire secondary system is working by turning your power key off and watching it fall on its face above 5K RPMs ...

Dynomite

Secondary Functional Test and Reconditioning the Secondary Actuators