New ZR1 owner

[jrd1990zr1]

Hi,

Just picked up my 1990 ZR1 about a month ago, obtained it from an exotic car dealer. On the 2+ hour ride home, I noticed a stumpling (hesitation) when I put my foot into it. I have now learned the previous owner had the fuel filter replaced due to gunk in it, the injectors cleaned and put on a dyno where it was claimed to make 345 HP at the wheels. I also recently learned that the car was stored with very little fuel for about 2 years.

The dealer wants me to replace the fuel filter again and I plan to check it for gunk. I have found a place which has a chassis dyno where we plan to put the car on with a new fuel filter and a pressure guage in line to see if there is a problem with the pump pressure under a load. This time of year I can't put it on the road.

Any thoughts on what the proper pressure should be if the pump is working properly?

Any thoughts on other possible causes to the stumpling problem?

Thanks for the advice.

[Aurora40]

Welcome to the club! I believe idle fuel pressure is around 45psi or so? It's been discussed, though, so a search might find the info.

[rbidwell]

I have read that stumbling at WOT can be caused by the rubber air dam being soft and collapsing. I just had a problem with rust in my fuel tank and had to have the tank removed and cleaned out. My "90 would complete quit running due to the filters on the fuel pumps being plugged. Also, I think if the secondaries fuel injectors and/or actuaries are not working properly that could also cause the car to bog. Might check plugs and wires also. Good luck. From Common issues ZR1 Net Registry: 22. TITLE - Lost of performance under hard acceleration.


YEAR(S) - '90 -'91



PROBLEM - Under hard acceleration you made feel a sudden lost of performance especially on hot days. This could be your air intake duct collapsing. This duct is thin and when hot becomes soft and under hard acceleration can suck close starving your engine of intake air. When you slow down this duct may open again and you start running fine.



CORRECTION - Replace the intake duct with a new one from GM. It's the same part number (#14104555) but seems to be heavier (thicker) in design.



SERVICE BULLETIN/RECALL - None


23. TITLE - Engine hesitation problems.


YEAR(S) - All



PROBLEM - Every once and a while the engine hesitates while accelerating.



CORRECTION - Of course there could be many reasons for this. But one that seems to be well known is AC platinum plugs. Owners have pulled plugs and found no platinum tip on the negative electrodes. Which when measured gave a gap of approx .058 thousandths. Sources at AC have said that the first couple of years they made the "so-called" 50,000 mile plugs they had a steep learning curve with welding the platinum "pucks" onto the center and side electrode. AC said that the newer double-plats are more durable.


Ron

[tomtom72]

Hi & welcome to the asylum!

Good stuff by Ron! I had the air duct problem on my 90, among other things. My car sat more than it was used by the orig owner, 8200 miles in 15 yrs! So I had quite a few things that went wrong in my first yr of ownership. To be expected if you start asking all the parts to come back from vacation suddenly! I must have looked like a slave driver to the car after the orig owner! I think it's warming up to me as I bought it presents!

One thing for sure is a Helm manual (GM) is a must & the NetRegistry site for the "common issues" and the "How To " section and the recall & TSB section. All worth reading! Oh and then zfdoc.com for trans info & Marc Haibeck's site for EEC theory. One thing I think Haibeck says about the stock injectors is that they don't react well to cleaning and remember that the 90 thru 92 injectors were designed before alcohol as a fuel additive...that is a cause for coil shorting = no pulse = not correct amount/or no fuel from that injector.

I have a Helm for my 90, so if you would like to know the book proceedure for the fuel pump pressure test PM me and I'll type it up & send it to you. Basically through you are looking for 48 to 55 PSI with KOEO, and 45 to 50 PSI motor running. Start test with cold motor & A/C off. Pull 2* FP fuse, pump should run about 2 sec to prim sys. Gauge should = 48-55psi. Install FP2fuse, both pumps should run 2 sec & psi = 48-55psi. Both steps should hold psi. That's the condensed version.

Do a vacuum check on the secondary port vac sys. Sys should hold 12" Hg. Also if the injectors are the problem a scan tool will tell you alot with the motor in "closed loop" & the tool hooked up. The O2 readings will tip you to bad injectors.


Tom

[jrd1990zr1]

Tom,

Is the "helm manual" the same as the red 1990 GM Corvette service manual? Any suggestions where I can get one or about how much I should expect them to cost?

Thanks, John

[rbidwell]

I am pretty sure the Helm's Manual that Tom referred to is the same as the GM Service manual. A few of the places you can purchase them are: a GM dealer, Eklers ($149.99 set), Corvette Central ($109.95 ?set), and Mid America Motorsports ($129.99). There should be two books. I'm sure there are several other places, but I just happen to have those catalogues on my desk. Hope this helps. Ron

[tomtom72]

Hi John,

Yea right on Ron!!! That's the straight scoop, John. Also Helm.com, the source. Ya gotta get a set, three books in the case of the 90's: electrical diagrams, General mechanical-covers L98 & LT5, LT5 specific mechanical motor service manual. The general book covers all the car's systems for C4 vettes and has the electronic engine control diagnostic & drivability stuff for both L98 & LT5's. It's worth the POE!

Gingle Bells guys!
Tom

[rbidwell]

I'm not sure how familiar you are with the ZR1NetRegistry, but there is a ton of information on the site that has been very helpful to me. On the left side of the home page if you click on General Info, then on maintenance, there will be a list pop up that will include information on such things as Tech manuals, ZR1 how-tos, common issues, ect. If you haven't used this you might check it out: http://listserv.corvettemuseum.com/archives/zr1net.html. The search function will usually yield information on just about any topic. Again, I hope this is helpful. Ron

[Aurora40]

You can get the whole set from Helm directly for like $105 plus shipping:
http://www.helminc.com

[ZR-1 Mack]

Welcome to another ZR-1 in Albany. This forum is the place to be if you have a question on your car.

I know of one other in your area owned by the NYS director for the ZR-1 Registry who trades in his ZR-1 for a snowmobile in the winter. You might even know him if you belong to a club up there.

I get up to Albany all the time on business so look for a couple ZR-1s (Red & Black 91's) running down I90 in the summer.

Post a picture when you can.