ZR1991

First, I want to thank the members, as well as Scott from Oregon, on advice last week when my LT5 developed it's strange stalling problem. For those who haven't read that thread, the car would start cold, or near cold, and run for a few minutes and suddenly run out of gas. Just so happens that I caught one obscure line in the service manual that said the second fuel pump in the ZR1 was for full power (which I already knew), but also for cold starting and running. Bingo.... if the number one pump is bad, then when the second one turns off, the car "runs out of gas". This diagnostic logic was helped along by the members, and in particular, I was given lots of help in finding the correct substitute pump, and doing the repair for about $70, instead of the $750 that the dealer wanted.

But now to this post. After replacing the pump, I immediatly noticed a difference in the engine's performance, but like I said, I know the psychology of something like this and I know it is easy to imagine all sorts of things. So now I have waited, and indeed the engine has changed.

This may be helpful to some of you. My ZR1 is the only one I have aver been in, and so I don't have any way to judge what is "normal". In my car, which I have owned for over 2 years, the transition to full power has always seemed too aggressive. I know when the secondaries open up, the whole point is to be aggressive, but for such a refined car, this just seemed too "crude". The transition was sudden and strong enough that if it occurred at the wrong time you could lose the car. It has happened to me, and is one of the reasons I have been less comfortable letting others drive it than even my Shelby Cobra, believe it or not.

Now to the point. With the new pump, the car is stronger before the transition, and though the transition is still noticable, it is controllable. The difference is not the full power performance, but the period right before. Food for thought... It is my opinion that the pump that failed was probably bad since I had the car (probably low volume, rather than pressure), and the car approached the secondary opening point "weakly", and the transition was therefore really startling. Again, this is always something from day one that I have not liked about the car. Now it is gone, the only change has been the pump, so one can draw their own conclusion.

So if any of you out there are like me, and fairly knowledgable about your ZR1, but haven't been in others, this may help. If you feel the full power turn on is overly aggressive, maybe even a little dangerous (depending, obviously on the situation), you may be right, and there just may be an easy fix.

For your consideration. In my case, the car is just as fast (faster in less than full power), and the full power transition is much more like I would have imagined it should be in this car. I am very pleasently surprised.

No one else out there may have symptoms like I did, I know this is very subjective, but in my case the difference is quite noticable, and the car is now "right", and I just wanted to pass on these thoughts.

Hope it benefits someone.

And, again thanks to the forum, always there to help!

USAZR1

Scott has written an excellent tech article w/photos about changing the fuel pumps for the next issue of our KOTH magazine. In it,he gives the different part numbers so our members can purchase these for reasonable prices.

ZR1991

Super,

Then I can be the first to endorse the helpfulness and accuracy of the information.

And like I said, for some of those who have been "alone" with our ZR1's, a closer look at this issue may prove to be a cure to a problem we're not even sure we have!

Thank You, Clint. Pass my thanks to Scott.

scotfab

I will mail you a copy of the KOTH article I am preparing. I value any comment you may have. It would be better to find any problems in it now before it goes to print. The is a whole different set of symptoms when the secondary pump goes out.
Scott
90 ZR1 #64 :seeya

scottfab

Been a while since I used the forum. Looks like I have two accounts too.
Scott
90 ZR1 #64

USAZR1

Glad to have you back,Scott. :cool:

phrogs

Isnt it satisfying to do your own work and not have to pay out the back pocket for an outrageaous sum of money :yesnod:
Great find Ill have to check that out on my car when i finaly get to drive it :lol: