More ZR1 woes...

N8nSM · 03-06-2006, 08:25 PM

Well I got her back together last Friday afternoon after replacing the fuel pump (and fuse that blew) the fuel pressure regulator, and the battery. I drove it to the gas station and then back to work. When I left the gas station I felt a slight stumble in it at low RPM's but nothing major. So slight that I was wondering if I imagined it. So after work on Friday I go to take her home and it starts missing and backfiring as I leave the driveway. Turned her around and brought her back to my work parking lot. I had too much to do this weekend to deal with it so I got back in it this afternoon.

What I have now is a misfire in low rpms (below 2000) only when I try to give it gas. It idles fine but give it a little gas and it starts missing. I'm thinking I may have clogged the fuel filter when I ran the tank dry (and fried the fuel pump) but I'm not sure.

Any ideas where to start? I'm going to double check the fuse for the fuel pump to make sure I didn't blow that again. It's got 60K on the clock and the original plug wires. They look good but I'm probably going to change them out anyway. I'm not looking forward to taking the plenum off again... ARGH...

Thanks all,

-Nate

90 Corvette ZR-1 · 03-06-2006, 08:36 PM

my advise, check the injectors. Put an ohm meeter on then and see if they come out between 12.5-14 ohm

dallas916 · 03-07-2006, 02:42 AM

Yup. Check those injectors. One may be leaking.

Aaron71771 · 03-07-2006, 08:30 AM

Plug wires are only good for 30K, according to the manual.

91redrocket · 03-07-2006, 10:30 AM

60K on the original wires ?

guinnessdood · 03-07-2006, 12:11 PM

Did you try tapping on the ECM while it is idling? MY ECM crapped out and it had very similar symptoms. If it was idling badly...I could tap on the ECM and it would straighten out...and then run VERY bad again. The engine barely ran sometimes toward the end of the ECMs life. Replaced the ECM...worked like a champ. I also had similar symptoms from the DIS Module (mounted on the underside of the plenum).

A26B · 03-07-2006, 12:34 PM

You can go nuts chasing problems without a few diagnostic tools and the service manual. I think there are at least 2 sets of service manuals on eBay right now. A new set is about $100 and well worth it.

Here's a short list of very useful tools:
1. fuel pressure gauge
2. hand vacuum pump
3. multi-meter

Check for stored codes before you start. Also, if a new problem develops right after you've worked on it, it is usually something that broke, bent or was improperly re-installed. Use your diagnostic tools with the service manual and back track your work.

You mentioned having to pull the plenum again....if you pulled it to perform the work you described, you may want to check the ignition module plug. It's not uncommon for a pin to be bent, resulting in misfires or no start. Sometimes a vacuum hose will develop a small tear or a plastic line will crack when it is handled during the r&r work.

There is a tremendous amount of knowledge here, always ready & willing to help, but the more information you can provide with diagnostic results, the better the help will be. GOOD LUCK!

N8nSM · 03-07-2006, 01:27 PM

I've actually been leaning towards injectors myself... =/ Didn't want to hear that!!

I'm going to try and get it back into the shop this afternoon and work on it tonight. Hopefully it'll let me drive it long enough to get it back where I have some tools!

Thanks for the advice all. Much appreciated.

And as for serivce manuals, what is recommended and where do I get it? I have the big Haynes manual for my Z28 and it's awesome but I couldn't find a ZR-1 manual from Haynes. Only the standard Corvette.

Thanks again,

-Nate

Crabs · 03-07-2006, 02:35 PM

Quote:

Originally Posted by N8nSM

And as for serivce manuals, what is recommended and where do I get it? I have the big Haynes manual for my Z28 and it's awesome but I couldn't find a ZR-1 manual from Haynes. Only the standard Corvette.

-Nate

Nate:

Here's what you need:
http://tinyurl.com/hpoy5

TomC
'90ZR1 #792

guinnessdood · 03-07-2006, 02:39 PM

Quote:

Originally Posted by N8nSM

I've actually been leaning towards injectors myself... =/ Didn't want to hear that!!

I'm going to try and get it back into the shop this afternoon and work on it tonight. Hopefully it'll let me drive it long enough to get it back where I have some tools!

Thanks for the advice all. Much appreciated.

And as for serivce manuals, what is recommended and where do I get it? I have the big Haynes manual for my Z28 and it's awesome but I couldn't find a ZR-1 manual from Haynes. Only the standard Corvette.

Thanks again,

-Nate

Nate - Get the actual ZR-1 manuals for your year car from Helms or on eBay http://www.helminc.com

tomtom72 · 03-08-2006, 08:31 AM

Get the Helms manuals for your 90. Also if you have access to a scan tool with the proper software for an ALDL system do a scan of the car from start up thru "open loop" to "closed loop" modes and you could see the trouble. At the least the scan will aid greatly in diagnosis.

I would do the scan before you spend alot of $ on parts you may not need. I have the 90 Helm set if you need anything looked up just give me a shout!