CHVYPWR

Whats the operating fuel pressure of an '87 mpfi 2.8?

1991tealRSt-topGuy

43-46 PSI

CHVYPWR

Maybe I should rephrase just a bit. What does the fuel pump itself put out?

1991tealRSt-topGuy

around 45-50 PSI......dont forget that your fuel pressure is dependant on engine vacuum (load) because of the FPR

AGood2.8

100psi /Vette pumps put out 125psi

CaliCamaroRS

That would be correct NEVER. Think first, then post.

AGood2.8

I'll state this again-
Standard tpi pumps with plastic internals put out 100psi

Vette tpi pumps with the metal internal gears put out 125psi

You fuel pressure regulator regulates it down to aprox 42psi for delivery to the injectors on a V6 fuel rail and everything else recycles back to the tank.

Thank you very much!

CHVYPWR

Easy guys, it's not that big of deal I'm just gathering basic info right now for my upcoming engine swap. I'm comparing the pressure ranges between the 2.8's pump and a Jeep Cherokee's pump for my MPFI into my Jeep swap.

Dale

iTrader: (12)

The mpfi and sfi pumps at that ftg on the rail should be between 40-47 psi running.

You will need a different fuel pump of some sort. I am currently swapping from tbi to sfi in my s10. I put a new pump in camaro, and took used pump from camaro for my s10. I rather the new parts be in the daily driver rather then show truck.

zoomzoom

CHVYPWR: I'm in the middle of replacing the 2.8 in my '86 Cherokee with a MPFI 3.1 this is what I can tell you so far:

From the Helms '90 factory repair manual: "With engine off (no vacuum to regulator) ignition "ON" pump pressure should read 40.5-47psi (the max pressure IS STILL being controlled by the regulator's spring, these directions are for testing pressure at the test port on the fuel rail)...... A vehicle with less than 24psi at idle will not be driveable."

So this is how I see it: All we need is a pump that will put out around 50psi as anything over 47psi is going to get returned to the tank.
For the sake of simplicity I swapped in a complete fuel tank, pump etc. from a 4.0L '89 Cherokee with MPFI. I just ordered a fuel pressure gauge today & will connect it directly to the pump as soon as it gets here. Again I believe that if I can get at least 50psi from the 4.0L pump I'll be in good shape.

Will keep you posted.

PS: Any thoughts on my post regarding A.I.R. pumps, how is you motor set up??

CHVYPWR

Thats what I was thinking of doing, using a 4.0 tank, sending unit & pump. Mine is also an '86. Thanks for the info, it clears alot up

As for the air pump, mines been disconnected for months, and the Camaro 2.8 I'm going to use doesn't have one. I don't plan on using it, there are no smog inspections here

TomP

Whut?! Dead head pressure of the V6 MPFI pump is 60 PSI. Go test it out if you don't believe me. I'm assuming you know how to test max pressure, of course. If you don't, let me know.

As far as to the dead head pressure of the v8 TPI pump, I thought it was the same; I'll look it up in my GM book tonight.

Oh and yes, the MPFI pump is different than a TPI pump. Are you talking aftermarket pumps?

CaliCamaroRS

State it all you want. I know how a regulator works. Hell, I've only seen 80-85 psi max. from a pump out of a '96-'00 5.7L CPMFI which puts out 64 psi KOEO. That's a bit more than any thirdgen pump.

Even if it WAS capable of hitting 100psi, how is this in any way valuble knowledge??? Nobody cares what maximum unregulated pressure is, smart guy.

AGood2.8

You are a mental giant- Think maybe you should slow down and read previous posts befor you start your crap with people. Here is a quote from Chvypwr up above that I was responding to you "smart guy".

CHVYPWR "Maybe I should rephrase just a bit. What does the fuel pump itself put out?"

And I gave him some figures that I read out of Hotrod Magazine a few years back. GM parts guys do not have this info to give you on stock pumps so they did an article on this years back on stock and aftermarket pumps. I specifically recall the article stating that most TPI pumps produse close to 100psi and the Corvette units were an astonishing 125psi. I remeber this distinctly because I was surprized myself to see the #'s that high.
EDIT:
If I recall correctly it was Turbo City that did the testing for them.

And TomP, Plaese don't mock my intellegence- a 4 year old can read line pressure from a gauge. I did state TPI pumps and not MPFI pumps thank you. I don't know off hand what a standard mpfi pumps puts out- I have a metal '89 Vette pump in mine because I learned years ago that they are made better and last longer- we all know what a bear it is to change them? or do we?

CaliCamaroRS

Apparently we both can't read because he asked about a 2.8 pump, not TPI. F*ck it, whatever....i've been pretty quick to jump on people lately so I'm going stop now. Either way, I still don't believe 100 psi unless I see proof.

AGood2.8

Look buddy, I clearly stated the figures that I gave him were TPI units so he would not think I was talking about the MPFI pump. I simply gave him some figures that I have read and figured maybe at least that coul help give him an idea what that V6 MPFI was based on standard V8 TPI's and Vette TPI's. Why is everyone so hostile on this forum- Its like I'm the new guy invading everyones click?

TomP

Cute; I've changed mine twice, dude. And if you missed that bit, then you're definately new here. As I recall, I didn't mock your intelligence, I offered help. I still don't understand why he asked about a 2.8 MPFI's fuel system, and you told him about TPI pumps.

A 4 year old might read the pressure off the gauge, and realize that's a real world scenario. If you want to go by something you read, hey, read away! I've never been a bench racer, though, so it's not my style. I need proof; otherwise I would've believed every moron that comes in here talking about how their motor is turbo'd. Next time you "state something again", ask yourself again why people seem hostile on this board.

Pressure doesn't matter anyway, flow would. That's going to be the main difference between pumps; the 5.0 pump flows more than the 2.8 pump- and if the search was working, I could probably find those stats from a question I asked a while ago on the TPI board. If any of us need 125 PSI for our V6's, I'd have to see a picture and dyno sheet for that motor, because it'd be a world famous v6.

1991tealRSt-topGuy

well AGood2.8, or should i call you AFreakinGoodTime

i think you should choose a new username thats not so obvious after being banned for what? the tenth time?

i think the only mental giant here is you

that is all i have to say

oh i forgot, please grow up too

have a nice day

AGood2.8

I thought to myself real good this time before posting

Anyway- Hotrod magazine is a pretty good source of info- its not like I read the info from this forum and repeated it.

Chvypwr- The pump may put out close to 100psi by itself but by the time the pressure tavels all the way to the front of the car and then upward against gravity then it will read possibly 70 psi just before the regulator thae longer and higher the fuel line setup, the less pressure the pump will put out because of resistence. To a certain degree, you can't put too large of a pump into the car because the regulator will only accept to the fuelrail what psi it is set at. The only trouble could be if the fuel line from the tank to the regulator can't for some reason handle the higher psi- like if it were all rubber hose.
Edit: (To clarify this more- If your fuel line is 6 inches long the pressure may read 100 psi at the start and end of the fuel line, however if the line is 8 feet long the it may read 70 psi form the start to the end. It doesn't come out of the pump at 100 psi travel a foot and drop to 90- then travel another foot and drop to 80..etc. If it reads 70 or what ever at the end then thats as high as it is reading at the pump because of resistence)

Tom, sorry but I explained above why I offered the TPI info and clarified the second time I posted that I was talking about TPI pumps. Pressure does matter as well as flow- Why?- because the injectors fire off of pressure.