After installing a Crane AFPR and setting the pressure to 52, I decided to tape the gauge to the windshield and see what happens in the 1/4. The pressure goes up when you blip the throttle, but as soon as you floor it and hold it down the pressure drops down well below 40 and stays there until you let off. Just backing off a little causes it to immediately jump up. It's funny when you're trying to tune in these cars the the things that start making sense. My tranny is not wanting to make the 2-3 WOT shift (next mod), so I've noticed that when I let off a little @~5200 rpm to let it shift the rpms would pick up as I backed off. Sounds like this may be the cause of that. The AFPR seems to be working fine...I put my hand vac. pump on it at idle and it decreases with the vacuum. Do you think it's time for the dreaded tank pull and new pump? What else can cause this? I asked the previous owner if Scroggin-Dickey had upgraded the pump when they did the motor swap and he didn't know. Suggestions on a new pump? GM or aftermarket? LPH? For those that have done it...what would you do differently, advice on the install?

I'm gradually getting this thing tuned in and learning more with every problem. I can't imagine how well it's going to run when I nail everything. After the tranny rebuild I've got to start thinking about a custom prom. I need to at least find out what's in it. He said it had been upgraded but didn't know the details. Thanks for any help!


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'87 Formula WS6 - ZZ4 TPI, ported heads, LT4 hot cam, 1.6RR, SLP runners, Accel lower, ported plenum, Edelbrock 58mm TB, pulleys, SLP cold air, headers and full exhaust, Koni yellows.

 

Sometimes the simplest things are over looked.

Did you adjust the fuel pressure with the vacuum line off and plugged up?

Have you changed the fuel filter?

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89 IROC-Z 5.7L
130,000 MILES
2.77 GEARS
K&Ns FILTERS
ALL FREE MODS
FLOWMASTER MUFFLER
PERFORMANCE RESOURCE CHIP
Best 1/4 E.T. 14.37 @ 95 MPH
Best 1/8 E.T. 9.22 @ 76 MPH
Best 60ft. 2.07

 

Oh, I forgot to mention the first thing I did was change the filter and it didn't help. I did set the psi with vac off and plugged. Just to be sure I hooked up a vac pump to verify the AFPR responds with or without vacuum. If I understand right, I should have the same psi at WOT as with the vac line off @ idle.

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'87 Formula WS6 - ZZ4 TPI, ported heads, LT4 hot cam, 1.6RR, SLP runners, Accel lower, ported plenum, Edelbrock 58mm TB, pulleys, SLP cold air, headers and full exhaust, Koni yellows.

 

I had the same problem.

Added an in-line pump and no more problem.

It's a hypertech, and it's noisy. My stock pump is still in the tank.

If your in-tank pump is old, then I'd put a good one in the tank. Mine was brand new.

 

damn, running at less than 40psi at WOT is running lean. dont to many WOT runs or you might eat holes in the top of your pistons. Id put money on it, that your pump is on its way out. Have fun dropping the tank i had to do it back in february. its a b*tc*

 

the inline fuel pump is going to be your least painful fix. Note that if you have some sort of physical restriction inside the tank, the inline pump isnt going to get you anywhere.

Considering the time involved in removing the tank, the inline pump is definitely worth a shot.

Stephen.

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stephen - 89 GTA - https://www.thirdgen.org/rides/index...ew&rideid=1321

 

Walbro makes most of the pumps that other peaple put there names on (including Ford and Chevy) I got my 255lph pump from jegs for 130$ and my head stoped hurting from the sound of the inline pump that I through in the trash.

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1991 Z28 ZZ4 with LPE superram base, SLP runners, LPE 58mm T-body,Random Technology ramair,TES headers,24#svo injectors,and just about every other bolt on that there is. Just got a ZEX nitrous kit!