Shady Mechanic?? - ZR1 Help
 

I recently bought a 1990 ZR1 (21K miles) that had performance issues with the secondaries and the "full power" mode. It stumbled and coughed and when pushed, the 3K RPM limit would occur and the SES light would come on then clear after backing off. The car had been sitting for a while so I though maybe the ethanol that may have been sitting in the secondary "system" may have been bad. I filled the tank with new premium and ran the crap out of it. As expected, it got much better the more I drove it. It eventual felt like it was close 100% except for an occasional hard stumble when the full power mode was first engaged and the pedal pushed. At that point I had not seen the SES light in quite some time even when applying WOT many times during a club cruise. I had originally made an appointment to have a local Chevy dealer look at it and decided to let them check codes even though it had improved drastically. The Chevy mechanic told me he saw a code 61 which made sense. We agreed to clear the codes and drive it a few days and see what if any codes returned. As luck would have it, as soon as I left the dealer, the Full power mode was back like it was at first and runs like crap. It may just be a coincidence but it went in running pretty damn good and now EVERY time I mash the pedal in FP mode, the light comes on, 3-4K limit and bad cough/stumbling. I hate to think that a mechanic would intentionally cause a malfunction to get work but......
Any thoughts on what might have caused the sudden change?

The secondary vacuum pump appears to come on then off as is should without any issue. I haven't checked anything else but I'm headed out now to get a vacuum test kit.

The Chevy dealer has quoted 2.5 hours to R&R the plenum and up to 2.0 diag time to find the problem. The good news is the seller has stepped up and agreed to cover the repair if becomes necessary.

I am pretty handy with tools but hesitant to do this myself.

Since you have a 90 I would think your problem is caused by bad injectors requiring a plenum pull. Since you are pretty handy I suggest you do it yourself, it looks a lot harder than it is and as a Z owner it is sort of a right of passage. Do some research on here and on the Zr1 registry regarding plenum pulls before you start, there is a ton of info on things to change while you're in there as well as the necessary parts and tools you'll need to do the job.

Welcome to the Brotherhood!!! :cheers:

Yep was thinking about doing it myself.
Just thought it was kinda odd that one day it ran fine and immediately after they looked it, it was drastically worst. I'm not sure if the previous owner had updated the injectors. I should be able to test them without pulling the plenum.

Shady Mechanic?? - ZR1 Help
 

Hello, Go to http://pnwzr1.net/PNWZR1.htm there is a step by step information for pulling the plenum. Also check out http://zr1netregistry.com there is a lot of information in the Forum section on pulling the plenum.

Tomcat 74 :flag:
91 ZR1 #906
http://pnwzr1.net

Thanks for the info. I seem to go from bad to worse.

I just took a short spin and now the car is performing poorly in the regular power mode. It started off smooth then it feels like I dropped a cylinder or two, then clears up, then when I get back on it it does it again. Would bad injectors cause such intermittent behavior?
I was looking at the test procedure for checking resistance. I'll try that first. Is there a way to physically look at the injectors to see if they are original?

^^^ Yes!, almost surely bad injectors dude. I had my car 5-6 weeks before mine started acting up- it just never got warm enough on my first few drives before I discovered the problem. Once the winding shorts out, they kind of stay that way unless you let it sit for months or if it somehow heat and contracts to un-short it somewhat. At anyrate, start pricing 16 injectors and the plenum gaskets and fuel rail o-rings.

even if you have another issue like a vac leak or old spark plugs, the injectors must be replaced in all of the earlier ZR-1's.

I know the previous owner knew about it on my car, but he so seldomly drove it, he never got around to spending on repairs.

Can you tell by looking if they are original?

Here's some stock and aftermarket pics. The orig ones are black and gray with a rounded top edge

http://www.zr1specialist.com/HAT%20W...eplacement.pdf

where I got my lucas disc type injectors (they were $550 in Feb this year-but no more).

corvette injectors dot com

where are you located and make sure you pop over to the registry site http://www.zr1.net/forum/ for more help

Marc Haibeck is one of the gurus of the ZR-1 who makes his living exclusively by working on and modifying the ZR-1s Here is a link to an article he wrote regarding the injectors...Which, BTW, sounds exactly like what you're experiencing - like me and so many others with 90-92s.

Just as a point of interest, when I bought mine it had been fitted with new injectors. Little did I know that they were NOS and it only took 3 years before they too went south. Summit Racing fixed me up with a new set of 16 Accel #150821s - $378 shipped (a year ago). It made a day and night difference in the WOT and idling.

Mozy over to the ZR-1 Registry soon as you get a chance!:thumbs:

P.

Thanks again for the help! I'm getting a list together now of what I'll need. I assume plenum gaskets and fuel rail O rings. Do the new injectors come with new o rings or can I reuse the old ones?
Funds are a little tight since I just plopped down my spare fun money on the car itself. Are the rebuilt injectors from FIC any good? Seems to be conflicting opinions on that.

I'm located in Nashville TN. From what I've been able to find, the nearest ZR1 shop is Near Lexington KY. Does anyone know of anybody closer? There a shop here called Vettesport that has my 85 (bad EGR valve) but he shys away from the LT5. He was recommended by a fellow NCC member.

I'll be doing this my injector job myself. My first plenum pull! Glad to know I have you to guys to help me out!

You should definitely replace all of the fuel system o-ring seals. The original seals are now over 20 years old. Since the engine was assembled new, ethanol blended fuels have become the norm. Buna-n was the preferred material for 100% gasoline fuel seals, but not so for ethanol. Viton is the preferred seal material when ethanol is present.

Check this out.

http://jerrysgaskets.com/store2/root...roducts_id=459

Will do. I just visually verified that I have originals injectors. I'll swap em out next week.

The things you have mentioned so far can be done yourself & you will be glad you did......but if you need a shop this is where I (I'm 80 miles east of you) go

http://www.automastersofbg.com/

Biggest mistake you could EVER make is taking the car back to a Chevrolet Dealer.Stop by the ZR-1 site and you wont need to go anywhere else.

besides checking the vac lines and secondary actuators, is there anything else I should check or do while i'm in there besides a good cleaning? The hard initial stumble in FP mode kinda concerns me. Would a sticky or failing actuator cause that?

I would recommend using a vacuum pump after the plenum is off to diagnose some of the bits under there before you buy anything besides the gaskets to do the job. You might have a big vac leak- that is pretty common as well. If it idles at 800, then probably not, but usually people change the spark plug wires, sometimes the coils since they are inexpensive, and of course the injectors.

Theres a simple procedure for checking the secondary system,fuel system before putting the plenum back on.Reattach-tighten all the fuel lines,back probe the ECM harness and find a PINK wire in one of the 4 wire bundles,maybe the third plug.Make contact with the pink wire so it can be grounded.With the key in the on position ground the pink wire and the secondarys will open,unground and they will close.The fuel line must be tightened up before this can be done.

Sounds great! Thanks