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 I had originally made an appointment to have a local Chevy dealer look at it and decided to let them check codes even though it had improved drastically.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

It idles at around 800 but it seems to take 5-10 sec to drop from around 1200-1500 to 800.

That's pretty normal. There are some measures you can take to alter the idle hang with custom tuning, but it sounds like you are most likely battling bad injectors or ignition problems. Even if it turns out to be ignition related, change the injectors anyhow- they all go bad (92 and below cars).

If your idle misses from time to time just sitting there as you listen, the injectors are also most likely bad. Mine cleared up and ran sooo much smother after I did mine.

It's just something that has to be done on these cars and isn't hard to do- it's just a $$ thing to buy the parts. All the other early regular C4 vettes also get this problem, but they only have to buy 8 injectors- and if rebuilt- pretty cheap cost.

When I did the injectors on my 91 at 8000 miles I also replaced the plug wires and coils at the same time,both with OEM parts.At maybe 7000 miles on the new G.M. coils one of them died so in went a new set of MSDs and I put the LT5 wires back on the car.At such low miles on the OPs car I wouldn't replace the wires-coils.Ive had my plenum of maybe 5 times,it to the point now I dont have to dig out the pictures to get it back together.

As mentioned, idle hang on a '90 is common, can be as long as 30 seconds, which seems like an eternity. It was an area of customer contention, and was addressed in later cars, and can be tuned out. There are a few things to check while under the plenum. All my vac lines were ok, when I changed injectors a couple of years ago, so I did not change any, but that's just a chance to take. There are a couple of "two vacuum line line couplers", that most guys put seperate lines on, because they are a common source of vacuum leaks. I put new couplers on, and they have always leaked, I need to change them to seperate lines. Aslo need to tighten, and put locktight on the bolts holding the cylinder case ventilation cover (#15 on pic) in place, as it is a source of oil leaks.....other than that, and a good cleaning, have fun! I generally think igniton parts should be good for 100K mileage from my experience in the indsutry back in the day, but here again that's just a chance. I really don't think the plenum pull is that bad at all, so I didn't care if I had to go back in later. I'll try to find a pic of the vacuum couplers. The vacuum block or couplers, is in the second pic just next to the electrical connector, and the A/C lines coming out of the compressor. You can see I replaced with new, but they still leak. I would replace them with two hoses. I'll add a couple more befoer and after photos...it should be as clean as the after photo when you get done!
:D

:thumbs::thumbs:

http://www.zr1netregistry.com/gifs/lt5_blowup.gif

http://im1.shutterfly.com/media/47a1...D550/ry%3D400/

http://im1.shutterfly.com/media/47a1...D550/ry%3D400/

http://im1.shutterfly.com/media/47a1...D550/ry%3D400/

http://im1.shutterfly.com/media/47a1...D550/ry%3D400/

Call Jon at FIC, he'll tell you. I think they come with orings on the secondaries, but not the primaries, or visa versa.

I have had the FIC rebuilt injectors in my car for over 2 years now and no problems. Flywheel was rattling before install and great afterwards. Drove the car to the 2010 Gathering from Idaho over 2000 miles. 27 MPG average and it runs great. Hope this helps.

Yup, Jim Van Dorn knows LT5s.

Here is an example of his work on my Beast. :thumbs:

http://i43.tinypic.com/2gvsmsx.jpg

Just be careful if you go and see JVD. I also started out just needing some new injectors (went with the FICs - outstanding) and before I knew it JVD had me talked into another 50-60hp that I didn't know I needed at the time. :lol:

Hey, what color is your car? While I no longer have my ZR-1, I'm in the Nashville area and might know its background if you got it local.

I now seem to have a vacuum leak that did not exist prior to removing the plenum. When I ground the pink wire to test the secondaries, as long as the secondaries are engaged, the vacuum does not leak down. When I remove the test lead to release the actuators, the sec. pump kicks on every 8-10 sec.

My sec pump will sometimes turn on once every 30 seconds or so (lately it has been sealed totally tight). There seems to be the smallest leak at the pump itself where the hose goes in, not so much the lines going to the solenoid...but check those. If you route the hose across the cooling hose wrong, that could also cause a bit of a leak at the coupler too.

A $30 vac pump tool can test all of the hoses.

Should I be concerned about a very slow leak? It seams to be at the solenoid. I tested both ways from that connector and it was tight.

This does sound like the solenoid.There is info on a replacement on the ZR-1 site.

I'd be curious as to what changed to result in the leak (albeit not at all severe). But, other than the annoyance it might cause me, technically, it isn't bad enough to cause a problem with the secondary operation. A vacuum problem big enough to affect secondary operation will be flagged by a code triggered by the secondary MAP sensor upon attempting to open the secondaries.

Secondary port throttles...Who needs 'em anyway??

FWIW, Many of the ZR-1 pilots, including me, have deleted the entire SPT system all together. That is another topic discussed at length here and on the Net Registry as well, so I'll just say that once the new calibration is installed and the system is removed, it never is a bother again.

I'm just sayin...

P.

I think it's the connector itself. I backed it out just a bit so that the little rings/nubs on the fittings on the switch hit new rubber on the connector. Seems to have solved the problem.

I'm making good progress and have the new injectors ready to go back in. When I was removing the fuel rail, I discovered that 3 of the 16 rectangular gaskets on the injector connector were missing from a previous service. I have checked around a few sources and cannot find these. How critical are they? Any ideas on a substitution. Was really hoping to get this back together today.

Google - Jerry's Gaskets

Tried him. He's only got a few from an old harness for private stock.

I typically don't do a lot of wet weather driving so it may just have to wait until the next time I go in there.

Can you make new ones?

Probably. I'll have to obtain the proper stuff to make my own. I called FIC and was told no big deal and not to worry about it.

I think Kurt White might have these.Since the injectors are also used in the L98,might just find these at a Corvette salvage yard.

Those are just bosch style square rubber seals on every injector from the 80's and early 90's. I scavenged a few from the junkyard as a couple inevitably fall into the valley abyss when you take off all 16 clips and plugs.

not ZR-1 specific at all.

I just got it all back together and ran it down the road. What a difference the new FIs make. WOW! Now THAT'S what a ZR1 is supposed to do!

Thanks to all the folks on this thread that provided the knowledge and support to help me complete my first plenum pull! Piece of cake!:thumbs::woohoo:

Yeah, next we'll have ya porting your own plenum and IHs, and port matching the heads (in place). With some headers and a tune, you'll be 'bout 400 hp at the wheels...Then, and then, and then.... Oh, what a sickness this need for speed is!!:D

P