i have a 91 z28 with a vortec tpi and auto tranny. it has about 15k on it.

about 2 weeks ago i pulled out onto the highway and started to accelerate and the car stumbled very badly then back fired very loudly. it would not run above 25mph so i limp the car home. at the time the temp, oil pressure and volts all looked good.

after the car sat for i while i went a cranked the car and hardly any exhaust was comming out the tail pipes so i figure the cat must be clogged. i cut the exhauset loose from infornt of the cat and started the car and other than being loud it seemed to run fine. i gut the cat hook it all back up and take the car out for about 40 minutes of hard driving. i did several runs from 0 to 60 and my times dropped about .5 sec so i am thinking problem solved.

next day i drive the car to work, store etc. it runs fine. that afternoon when i pulled out on the highway to accelerate it did the same thing!!!!! now what?

some time before when i setting the fuel pressure i noticed the guage jumped wildly and it was suggested that my fuel pump, which had 155k on it may be going bad. now with this problem i am told by someone else that, yep it is the fuel pump.

today i had the new fuel pump, screen, etc installed. after installing the pump we tried to set the fuel pressure. when the car is turned on, not started, the pump goes up like it should but it does not hold pressure, it will drop back down to zero rather quickly. the pressure was set at 35-40 psi and when you tried to start the car it would cut back off. we finally set it at between 56-60psi and then the car ran fine.

after a quick test drive with no problems i take the car home. about 4 miles into the trip it stumbles again. not as bad but it will not run above about 45mph.

anyone wanna suggest the next part to be replaced??????

thanks

 

Turn that fuel pressure down to 42 pounds.
Replace fuel filter.

If you prime the pump by turning the key on and you notice that your pressure leaks down rather quickly, then you have 1 or more bad injectors (stuck open).

If this is the case, change your oil immediately and dont drive it until injectors are replaced.

Just some advice!
Good luck!

 

we were unable to adjust the regulator to anything between 40 and 56psi. even minor adjustments went to the extrem.

fuel filter has about 1500 (1500 is correct not 15000)on it. do you still think it might be the problem?

anything below 40 and the car would cut off.

the injectors were all installed new when the engine was installed but i will do a search and find out how to check them.
could a bad injector create this kind of a problem?

could the afpr be bad?

thanks fer da tip badz and yes you do have a bad z!!

 

Yea, it could be a bad AFPR. But, I had the same problem with my stock injectors. I replaced them and the fuel pressure held.

 

these were switched to new 24# because the old engine was 305. just like the engine they have about less than 15k on them.

any ideas on why would could not adjust the AFPR to any place between 40 and 58?

i am leaving for south carolina in a couple of minutes but will check back tomorrow nite.

i'preciate it!!

 

It could be the AFPR. Change it out, reset fuel pressure, and see if it holds.

 

just got back in and got your message. i will try that next. if that doesnt work i will start with the injectors next.....sigh

 

ok, i spent the last 2 hours trying to see if there is anyway to check an AFPR and have not found one. is there anyway to check it or do i just get to buy another one and hope that was the problem?

(no wonder people just put a carb on)

 

I would suggest a Holley billet TPI AFPR from summit. Thats what I run and it's awesome. It has a dial that you can turn with your finger vs. having to fish a wrench in there to turn a bolt.

Unfortunately I do not know a way to test the diaphragm in there to see if its bad. You might just have to buy a new AFPR.

Get the Holley piece, it's worth it!

 

hello.....summit.....yes i'd like to buy a holley afpr.

thanks z it's on the way.

yes the little wrench was a pain in the azz. : )

 

No prob!

Let us know how it turns out when you get the Holley AFPR on the car!

 

for those interested, i reposted this with updates under the TPI section titled "VERY fast fuel pressure drop".

the problem still ain't solved so....feel free.

 

mines doing almost the exact same thing.........ill keep checking the posts to see if anybody replies with some answers....i have the holley afpr and it is a nice piece........thanks