Chasing Hesitation/bog

[FixxerAuto]

Hello,
I have a 90 ZR1 that sat for about 3 years. Unfortunately, after start up, the car was drivable with a shaky idle and misfire/ lean backfire when hot. As well as a large hesitation when trying to use the secondaries.

So I replaced the fuel pumps with new Delphi pumps, replaced all the fuel injectors, plug wires, and coil packs. I checked and regapped the plugs but didn't really find any reason to replace them. I checked all of the vacuum components in the secondary system- replaced check valve. My vac pump no longer works, but it has never worked in the time Ive had the car... I found one fuel injector at 4 ohms and 4 others at 8 ohms which, i thought, was my problem.
Well, the idle is fixed and there is now no cough/ hesitation when i blip the throttle. And, until the car fully warms up, i can get some good full throttle, valet key on launches. But as soon as she fully warms up, I get a big bog when trying to accelerate wit the key on. Key off, everything is fine.
Fuel pressure is in spec when idling and bliping the throttle. But the pressure quickly drops to 0 when the engine is turned off. I wonder if the check valve is not holding on my secondary pump, causing an internal pressure leak when the pump shuts off? So, i run out of fuel before the secondary pump kicks back on at 3500rpm? Due to the loss of fuel volume through the failed check valve? Is it possible that my pressure regulator is allowing too much fuel to flow back to the tank to maintain pressure?

The car starts to accelerate and pushes me back in my seat, but i am quickly thrown forward against my seat belt. Any ideas?
Thanks

[Paul Workman]

Fist things first: let's eliminate the check valve or whatever the reason it isn't holding pressure with the ignition switch turned off. (I had a bad check valve on a brand new fuel pump once. Just because a new part was just installed,, you can't assume it works properly. Anyway, with mouth back pressure on each individual pump, the pump with the bad check valve was immediately discovered.)

Then I'd want to hook a fuel pressure gauge to the fuel rail and tape the gauge to the windshield and go for a drive. At light throtle, pressure should be mid 40s. And, at WOT you want to see low to mid 50s. This will verify the entire fuel delivery system: pumps, regulator, filter, and fuel lines. Failure to provide pressure means isolating each delivery part and verifying they each are working. (My fuel filter was nearly plugged at just over 40k miles.)

Unless you install a "secondary delete" chip and tie the SPTs open (tie-wrapped), the integrity of the SPT system is important. You can get by w/o the vacuum pump upon initial WOT operation. But, depending on how tight the vacuum network is, the secondaries may not stay open without vacuum from the plenum or the backup pump. (And, you should then get an SES light and a code 61 (no vacuum).

So. Fix/replace the pump and assure the integrity of the rest of the SPT system first. Or! Elimimate the entire SPT amd install a "SPT DELETE" chip (and NEVER be troubled with it again).

Enough 4 now. Ned to a eliminate the fuel issue first.

[FixxerAuto]

Thanks for the response, Ill pressure test the pumps at the fuel sender. I think the pumps are lifetime warranty, so i should be able to get a new one for free. You brought up a good point with the filter. I think mine probably has 15 or 20K on it on top of the stale gas that was in it earlier- Ill get that changed and report back.
THanks

[Paul Workman]

If fuel and SPTs are eliminated, the next thing might be that "accordion" tube on the throttle body collapsing. THAT created a significant BOG on my "new to me" 90 ZR-1.

Marc Haibeck provides some wire hoops that go inside the tube to keep it from collapsing. (However, I built an inner sleeve out of air duct sheet aluminum and a couple pop-rivets. Smoother air flow and works like a charm!)

[FixxerAuto]

I suppose the way to check that would be to do some test launches with it removed and see what happens...

[Ccmano]

Do what Paul is telling you. Had the accordion tube collapse on mine, felt like I had no secondaries at all. Tho this does sound like a secondary pump/pressure issue.

Btw, your not that far from me, I’m in Reno. Ever make it down here?
H

[lfalzarano]

Jerry sells a solid one that doesn’t collapse, and you can save the accordion one for NCRS.

http://www.jerrysgaskets.com/duct-si...lue-90-95-12a/

IMG_3140.JPG

Attach it to a SLP induction filter system and the car will be ready to rock! Save the old plastic one for NCRS also.

https://www.summitracing.com/parts/sle-21028

IMG_3141.JPG


Lou

[FixxerAuto]

Just wanted to give an update. So I installed a new K&N fuel filter and a new battery (I thought that maybe the old battery may have had a loose plate). I also pressure tested the system and found that it is now holding pressure well. I figured out a way to easily isolate the fuel sender from the pressure regulator as well as a way to get all of the fuel out of the lines to change a fuel filter.

First I connected my pressure gauge to the fuel rail and got it where i could see it. Then i went around the back and rigged this up. I slowly opened the valved and watch the gauge go up to 55 and listened to all of the gas blow out of the return line and into the tank. I didn't open the valve any more than was necessary than to achieve the 55PSI limit of the regulator. After about 10 seconds, there was no more gas flowing back into the tank.

MVC-698F.jpg
I Observed the rail holding the air pressure well at 45PSI
MVC-700F.jpg
Then as a final step, i rigged this contraption up to test the fuel pump check valves and sending unit. I only opened the valve enough to build ~50PSI and shut it off. I then observed that it held pressure well.

MVC-701F.jpg
As a result, there was not a drop of fuel spilled at the filter upon removal and replacement

[FixxerAuto]

Afterward, i used the fuel pump prime connector to pressurize the system. After, two hours the system bled down to 35PSI. Id say that is pretty good. Im at a loss as to why it was bleeding pressure the last time i checked it...
I also replaced the secondary vac. pump. The pump kicks on for about 2 seconds then off for about 3. I think the leak must be the check valve. but it is much better than it was. And this is the first time that the pump has ever worked in the 12 years that i have owned the car.

So, the car seems to be running a bit better. The hesitation is pretty much gone but the bog is still there. The bog only occurs now when accelerating through left turns. I think i may have to make an ALDL cable and do some data logging to figure this out...

[A26B]

Good methodology, but I’m concerned about using compressed air on the fuel system. Even turning an ordinary flashlight on over the gas tank to have a look inside is dangerous. If you must look, only turn the flashlight on or off when well away from tank.


Sent from my iPhone using ZR-1 Net Registry