88 z24 fuel issues - Second Generation Forum

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88 z24 fuel issues
Wednesday, April 22, 2015 5:46 PM
Hey guys picked up an 88 z24 with an apparent fuel issue. Has spark and when carb spray is shot down the throttle body it will start off of that for a second.

Previous owner had replaced the fuel pump and supposedly checked pressure and checked the regulator by applying vacuum to it and checking pressure change as it was applied.

At this point, the original owner concluded it had bad injectors, got a set of used ones and went to put them in. When he pulled the plentum to do this, he claims the injectors were stuck, so he put everything back hoping something magically fixed itself ( which it did not) and he sold the car to me.

Upon looking the engine over I noticed he had left one injector plug off, which could not be accessed with the plentum on. From here I dug in, got the upper intake off and had access to the fuel rails and injectors. I ohm'd all of the injectors, which gave consistent appropriate readings within spec. I also checked the harness with a noid light and determined all injectors were also getting a pulse. I plan on removing the injectors and rail for cleaning and replacement of seals, but before then I decided to look for pressure

My haynes manual gives that warm and at idle it should have 41-47 psi, and with the vacuum line to the pressure regulator removed it should rise by 5-10 psi

Given that the engine was not running and the plentum was off, I was not able to warm it up or let it idle to check it, nor did I have a vacuum line hooked up to the regulator. I got a reading of 40 psi after cranking 3-6 seconds a few times. With the specs from my book it looks like I'm 6-11 psi shy of the low end of the spectrum, based on the understanding that with no vacuum to the regulator I should be seeing 5-10 psi more than 41

I was hoping someone with more experience with these 2.8 mpfi, or fuel injection systems in general, could answer a few questions and possibly lend some advice.

A: Do you think the cool engine vs warm engine would result in a lower fuel pressure reading

B: Do you think that just cranking would result in a lower reading or a higher pressure reading vs idling

C: If the 40psi is in the ballpark of an accurate reading, would that 6-11 psi shy of the rated spec keep it from starting?

If anyone has any input it would be greatly appreciated, Next im gonna remove the rail and injectors to clean them, unless theres anything else anyone thinks I should check while I still have the plentum off.


Re: 88 z24 fuel issues
Wednesday, April 22, 2015 9:18 PM
A touch tired but some points.The car has to run to show the fuel pressure is within the specs of 41-47,however your saying it is low based soley on (cranking it).The car has to idle and then at this point it will drop back from 3-10psi.I personally would just replace the injectors as the age of the car.I also would spend the couple of bucks and replace the fuel filter!You did not mention if the PO had done this even though a new pump was done.I will say I am not super fluent with the 2.8's fuel system,but if your spraying fluid in the tbi and it runs I think your issue is more mechanical and not like a relay or ecm issue.I could be dead wrong but just reread in your Haynes checking the fuel system as I think you misunderstood the info.Just my quick overview.I bet james cahill could answer this easily.

Re: 88 z24 fuel issues
Thursday, April 23, 2015 5:22 AM
Thanks, I didn't mention in original post, but new filter too. I didn't think my measurement at crank would match the hayne's at Idle specs, but I was curious if anyone had any thoughts on the 40psi at crank.
Re: 88 z24 fuel issues
Thursday, April 23, 2015 5:25 AM
i have an86 with the 2.8 and have found it a bit tempremental. imo not gms crowning acievment. do not assume anything the previous owner said or did to the car is true or correct. if you have fuel and spark the other part of the equation is air. can your engine breath? it might be as simple as a clogged exhaust. are there any touble codes? you can retrieve them by jumping thre test port with a paper clip and counting the flashes of the dash cel kight. the v6zz24 website is a great source of infor on these cars and i would check there. some 80s camaros and fieros used these engines and you could check some of those forums also. good luck and keep us posted on your progress.some pics would be great too. once you get it running im sure your gonna love it
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