JANO

Hi to all
I would like to ask you for help.
Here is problem with my 94 Z :

Car start normal and run normal but when engine touch 175 F suddenly
engine lost power -cant drive anymore just have only 900 RPMs......
I always have full power-Haibeck chip and there is no ses codes.
This problem start few miles after i take fresh gasoline .

thanks,Jano

glass slipper

Sounds like your primary fuel pump is failing. When you start the engine, both pumps are running. If the coolant temperature is above ~180°F (I can't remember the exact temp), the secondary pump shuts off after two seconds. If the temperature is below ~180°F, the secondary pump continues running. Since you don't have a problem until close to 180°F when the secondary pump shuts off, it's most likely the primary pump. You can pull the fuel sender unit/fuel pumps out and swap pumps to get you going again and it's a no cost temporary fix. Just don't engage full power...leave the power key in the normal position. But at least you can get where you need to until you get a new pump. I did this temporary repair on the side of the road at the very beginning of a 400 mile two day trip out of town and had no problems. Only took me an hour...I enjoyed my trip (a ZR-1 gathering) and fixed it when I got back. Good luck with it!

Edit: I just saw where you have a chip with "full power" always on. In that case, just don't take it over ~3000 RPM and you'll be more than safe.

JANO

hi & thanks for fast reply.
Which pump is primary ...........upper pump or lower pump ? :o

glass slipper

What year is your ZR-1?
Also, if you're just switching them to get back on the road, it doesn't matter right now. Of course when you actually replace it, you'll need to know.
I'm going to look up the wiring diagram and see which color wires go to the which pump. I only have a set of '93 and '95 FSMs so I'm going to assume the color of the wires are the same for all six years.

I'll be back in a few minutes.

glass slipper

The gray wire goes to the primary pump and the light green wire goes to the secondary pump for the '93 and the '95 so it's probably the same for all years. It's been 10 years since I was in there and if I remember correctly, it was the bottom pump. The color of the wiring is the most accurate way to do it though. Hope this helps.

JANO

my Z is 94.
I came back to my home hardly , you can image how like was driving with 900RPMs 2 hours....
I would expect any SES codes , any possible to be something else before Im going pull out
the fuel sender unit.... Definitely problem always start when water reach 176 F...
thanks & regards ,Jano

glass slipper

It's always possible that it could be something else, just not very likely. Your symptoms match up with the secondary pump being turned off exactly. As long as your secondary pump is running, everything is good...turn off the secondary pump and you're barely limping along on the primary pump. Looks like an open and shut case for the primary pump on its last legs. Go with the most likely and switch the pumps to see if your problem goes away, shouldn't take more than an hour if you're handy with tools. Just be careful when you're pulling the fuel sender/fuel pump assembly out...you have to twist and turn it to snake it out of there. It's almost as bad as a Rubics cube but like the Rubics cube, once you figure it out, it's a piece of cake. Just have to find the right combination of twists and turns with a little bit of gentle persuasion here and there.

Hooked on Vettes

If the primary fuel pump is defective which could be causing the engine to not run above 900 rpm due to low volume/pressure try this.

For test purpose, remove the fuse on the right side end of the instrument panel labeled ENG 2. This fuse is used by the Fuel Pump relay #2. Removing this fuse will disable the FX3 controller, the EBTC module and the Secondary Air Pump. Removing the fuse will prevent the PCM from shutting off the secondary fuel pump when the engine is above 176 F. If the engine now runs normal that would point to a bad primary pump.

glass slipper

A much easier way than switching fuel pumps!!! Great suggestion!
One question though...where were you 10 years ago when I did my roadside fuel pump swap???


I've seen that relay in the schematic for years showing it passing power to the secondary fuel pump with the ECM not grounding the relay and never made the "connection" that the ECM grounded the relay to turn the secondary fuel pump OFF. I just had it in my mind that the ECM/relay turned it on. Sometimes the most obvious is the hardest to see.

Thanks for shining a bright light on it for me and JANO.

JANO

yes, i removed fuse nmb 21 and engine was running "normal" over 176 F SO DEFINITLY
IS PRIMARY PUMP BAD...............
THANKS both of you , very appreciate your help.
best regards
Jano