dallas916

After testing (both leak and ohms) and replacing some leaking injectors (and a wobbly oil sending switch) I finally got the Z out last night for a drive. It was almost as bad as before. Still the pup-pup-pup at idle, which got a stronger at cruising. This time, however, it did not bog down when accelerating.

I got on the highway...not a car within miles...thinking I'd blow it out a little. Shifted down into 3rd, stepped firmly on the gas, accelerated smoothly up to about 6000 rpms...then a little "pop" sound, the "service engine soon" light came on, and I just cruised for another 10 miles out and 30 back feeling the distinct lack of ZR-1 type energy.

I stopped at a store for a couple of things, engine had to turn faaaar more than usual to start. Ran it home...the sevice engine light had gone out...and put it away. Heard a faint "ticking" sound in the garage, but it was 0400 and I wasn't in th e mood to do any investigating. Haven't tried to pull the code yet.

No gas smell, except at the moment of first startup. Car had sat for several weeks again. Has about 13 gallons of fresh Chevron and a bottle of Techron in the tank.

The little "pop" before the SES light came on??? The lack of power? "Starving" at 6000 rpms? No vacuum leaks that I can detect...pump runs at first power, then quits. Whadya think?? Oh, yeah...light backfire through the exhaust when decelerating in gear (light popping).

drd21968

likely injectors

8388

Checking the codes will hopefully be your best clue in figuring out the problem.

dallas916

OK...got the code last night. 55. So, I have a lean condition and maybe starving for gas at WOT or higher rpms. I haven't run the fuel pump tests yet, but I can't believe that all of a sudden either one would start messing up.

I think I'll start by checking all the ECM connections for proper fit.

Any other suggestions???

8388

Hook a fuel gauge to the rail, and tape it to your windshield and then take it for a spin. You'll get to see what's happening under a load that way. If your injectors are firing correctly, lack of fuel is more than likely the problem.

dallas916

I'll try that.

95ZR1

Also make sure a backfire didn't blow a hose off the back of the plenum.
Wouldn't it be great if it was that easy? Prolly not.

USAFPILOT

sounds like exactly what happens when the secondaries dont kick in.

dallas916

I did check the hoses and they are ok. I know there's not a vacuum leak in the 2ndary system 'cause the pump shuts off and stays off right away. However, you are right that the secondaries are probably not even being activated. Anything that stops the fuel flow will shut down that part of the system. If it's a secondary pump I'll just replace it. I'm hoping it's just a connection. That said, the car has sat so much I could be a victim of plain old crud somewhere keeping the 2nds from kicking in. It sure doesn't have the kick it normally would.

My son and I will run through the whole troubleshooting path to be sure. Hopefully, by Sunday it will be breathing fire again.

glass slipper

It sounds like a bad secondary fuel pump which is easy to check...no need to tape a gage to the windshield and try to look at the gage while accelerating at full throttle. Just pull the "ENG 2" and "Fuel Pump 1" fuses and only the secondary fuel pump will run in this configuration. You can check for fuel pressure from the secondary fuel pump without even starting the engine, just turn the key to "ON" and the secondary fuel pump should run for about 2 seconds which is enough to get a pressure reading. I'm betting the pump won't even come on.

You can also check it without a fuel pressure gage by starting the engine and pulling the "ENG 2" fuse first and then pulling the "Fuel Pump 1" fuse. If the secondary fuel pump is completely dead, the engine will die...electric fuel pumps don't often "partially" fail although it can happen.

Don't be surprised when the check engine light comes on during this test...the ECM monitors fuel pump voltage via the circuit to the primary fuel pump. Since the "Fuel Pump 1" fuse is pulled, voltage will be zero and a DTC 54 (fuel pump circuit low voltage) will be set.

Good luck with it!

dallas916

Thanks, Richard. I'll definitely try the pump test first.

8388

Fuel pumps don't always just die, they can operate but not be moving the right amount of fuel. You cannot duplicate a load while standing still. Watching the gauge under a load serves several purposes, one them being a before and after record of the pressures during various gears and rpms. He will also learn whats normal for his car. Fuel pumps can and do partially fail, I see it all the time, especially if it's an electrical issue.

glass slipper

Most fuel pumps do "just die" when the electric motor dies. If the problem is on the pump end, it'll may even still make rated pressure under no load but not provide sufficient pressure at higher RPM under full load. Out of all the failed fuel electric pumps I've seen, I've only seen one that was on the pump end where it could keep up under normal driving but fell flat at high RPM/full throttle. All of the others were a dead electric motor and it did nothing...I like playing those odds.

I just said the same thing as you did above...I also said the same thing as I said in my quote below so I don't know what part of "don't often" and "it can happen" you don't understand. If it passes the simple idle test, then he can proceed to the "taping the gage to the windshield test". I'm a big proponent of going after the low hanging fruit and the method I outlined will reveal a completely dead electric fuel pump very quickly and very easily...sorry, I'm lazy like that.

8388

Here are my thoughts based on what I read :
He obviously has a pretty good load on the engine, and the secondaries are for sure open even under 3k rpms, pulling through 6k rpms when he notices a "little pop" Both primary and secondary injectors are operating at that point, or he would be explaining about issues south of 6k rpms. Pulling fuses which a good method of eliminating fuel pump failure, may not explain other causes which are normally found under a load. Not saying it's not a secondary fuel pump failure, but usually when that happens , he would be noticing some hesitation on the way to 6k rpms plus.

glass slipper

To address the part in bold first, the primary fuel pump is capable of supplying sufficient fuel to the primary AND secondary injectors up to about 6000 RPM so there would be no issues below that point. Pulling fuses is a quick and easy way of possibly finding the problem at idle...you don't have to recreate the problem exactly. If the problem doesn't manifest itself at idle, you've only lost maybe two minutes of your time

I really think we're in agreement and appreciate your thoughts. We've all had our experiences with these cars and that's the best thing about this forum. One of us is bound to have had the same problem and it only helps everybody involved to hear everything...experience is a good thing. One of us is going to hit on a solution sooner or later and that's a good thing for the OP. I've had the experience of a secondary fuel pump delivering no fuel and the symptoms were exactly the same as his first post right down to the RPM at which the lean condition hit...and there was no hesitation during the run to 6000 RPM. It pulled strong, popped, set the SES, and fell on its face as the secondary throttles were shut/disabled and remained disabled until it was shut off and restarted.

dallas916

My son and I finally got to test the #2 fuel pump. It powers up at "key on", and pushes 50+ lbs. I thn started the Z and warmed it up a bit. It sounded very good at idle and when in raising the rpms. It still, however, bogged when the throttle was pushed hard from idle, and backfired once (sounded like through the intake).

Haven't driven it yet...maybe today.

Tonite: 0130. Took the car out for a drive. Hit WOT 8-10 times. Easily ran to 7000-7500 rpms with lots of pull and no codes. Idles smooth and drives like a dream again. Somebody musta been prayin' for the "Little King". Felt so darn good!