well, been having problems with my new engine and one of the causes is that i have WAY too much fuel going in there. found this out yesterday when i drained the oil for other reasons. i have an LT4 hotcam with 1.6 rollers in it, pushing about .525 on the lift. fuel pressure (static) was set at 43 w/no vacuum. then with engine running, set at 48 w/NO vacuum. i was told yesterday that this was way wrong, that it should be set at about 25 WITH vacuum. i have a holly afpr on it... (i'm talking about my 91 Z 5.7 TPI) i need to get in the ball park for fuel and will work on getting the tuning with air/fuel mix set. no, i don't have a custom chip - it is stock. thanks for any help... again...

KAM

 

Well, don't know who told you 25# with vacuum. Mine is set at 48 psi everything hooked up, vacuum on the AFPR and the engine idling. Then I taped the gage to the windshield and did a couple of WOT runs to make sure it was staying there, it did climb to about 50 then settled back down. Stock I believe is 42 or 43 at idle. I know some go to 37 or 38. If you have gas in your oil on a new engine I'd be very very concerned about more than fuel pressure.

 

yea, something definitely ain't right... had the injectors cleaned and serviced, too... any ideas???

KAM

 

I'd be looking here...Low vacuum with stock calibration would tend to run pig ritch I would think especially at idle. ECM is likely to think you've got your foot in it. Fuel in you oil simply is a sign you not burning all the fuel. I have the same cam in a 383 and I
bet it wouldn't run on a stock chip.

 

The correct method for setting fuel pressure is to:

1) connect the fuel gauge securely with no fuel leak
2) start engine, let engine idle down to proper idle RPM
3) disconnect & plug vacuum line from plenum to AFPR
4) read your fuel pressure.

Stock fuel pressure should be at 43 to 44 psi.

With mods, you might want more than stock fuel pressure. Also, realize that the fuel pressure is set for the correct AFR at WOT, not for idle or for cruizin around. While idleing and cruizin, the ECM will correct the AFR to 14.7 (this is your BLM value) as long as the ECM does not have to out of range on its correction factor, which will get you a warning light.

Do a cylinder compression check and bleed down. Maybe you have worn piston rings. That would explain fuel in the oil.

 

Do some searches that cam has been tuned by others on this board. you will have to get into prom burning if you want that thing to run like its supposed to.

The thing is with sd and a bigger cam you get real rich at idle. Its easy to go in and find the kpa and rpm where the car idles and pull fuel in the lower ve table.

Try LOWERING the fuel pressure down from 48 a little at a time that should help the idle. BUT MAY GO LEAN ON TOP Take it for a drive to see how it runs.

Putting money into the motor is only just a start with sd. It will take more work to get it to put out the power it should with tunning. If your not going to get into tuning you might just as well put a carb on it. No way around it.

 

MikeH, Like you said, you really want to set the fuel pressure for WOT (AFR between 12.8 and 13.0), not idle. You do not want to go lean at WOT, its an expensive leason. If the engine runs way to rich at idle (or lean), a custom chip is most likely required.

 

Yes that is the proper procedure to follow, I get it in the ball park by running the fuel pump with the engine off.

let it run until the coolant fan turns on, or the Temp gauge reads >190°F this insures that the ECM is in closed loop mode.

 

Hey thunderstick you never said what size fuel injectors you are using .?
Another possibility of fuel in your oil could be a bad injector or injectors that are constantly leaking. Invest in a fuel pressure gauge.

 

rogsgta:

You are very correct, great call. You can check for a leaking fuel injector by attaching the fuel gauge, start the engine up, let it run for a minute, and shut it off. Watch the fuel pressure. It should not fall to zero for about 15 minutes.

rgarcia:

That is the alternate method, just key on (do not start engine) and read the peak fuel pressure as the fuel pump comes on. But, with this method, you do not have time to sit in the drivers seat and key it on and catch the fuel pressure as you walk around the front of the car. You need to be able to read the gauge right from the drivers seat, or have someone help you. I've used this method many times.

 

Don't need help.
The key doesn't have to be on, apply 12volts to ALDL terminal "G" to power the fuel pump. This is I what I do when I need to empty the gas tank.

 

My cam is hotter than that and my car will run just fine on the stock chip. That was with 26# injectors, haven't tried the stock chip with the 30# injectors, but I think it would still work fine if I dropped fuel pressure.

 

Actally no the comp cam in your sig. is similar but slight smaller than the HOT CAM. You also realize that cam is much milder in
a 388 than a 350. I'd be willing to bet your car would run alot better with a tuned chip. My moneys still on the calibration.

 

rgarcia, you are a very resouceful guy, I would never have had that of that one, thanks.

 

Not, just lazy, and you know your friends are never around when you need a hand, but when I pop a top there always seems to be one there with an open hand.(beerchug smiley here if we had one.)

If you need any lazy ideas just ask.

 

LT1's... had 'em serviced by rick @ cruzinperformance, came back all good. i have a f/p gauge. initially set press @ 43, then 47ish with the engine trying to idle (no vacuum). why is f/p set with no vacuum?

KAM

 

Because 47ish psi is what is needed at WOT, at some point in the rpm the vacuum begins to decrease and the idle 38ish psi fuel pressure will increase until it reaches 47ish psi at no vacuum.

 

[ why is f/p set with no vacuum?

KAM [/B][/QUOTE]

When you (wot)romp on the gas there is very little to no vacume present inside your intake. So when you remove the small vacume line going to your fuel pressure reg your are simulating the pressure your motor will see at full throttle. You would like to know that it does increase not drop with out vacume. I run a high out put pump as well as an inline pump my fuel pressure increases at least 10 psi with out vacume. 47 at idle and 57 w/o vacume.
rob

 

You have a MAF car and they are more forgiving on mods with a similar cam than an SD car (as the original poster has). 26# injectors are not too different from the original so it won't adversely affect the eprom too much. However 30# would work far better with an eprom change. Even a bone stock MAF car will respond very well to eprom changes.

 

I would say that it should not fall to zero in a MUCH longer period than that. I recently had a bad injetor and it took about 30 minutes for the fuel pressure to fall to zero.

With the injectors cleaned I still have pressure (though only 20#s) in the rails over 24 hours later; and I still feel it is dropping a bit too much.

 

Glenn, since fuel is incompressible, it only takes a minor leaking injector to drop the fuel pressure pretty fast.

 

A leaking fuel injector isnt the only reason you can lose fuel pressure.
A leaking or cracked seal on your fuel regulator is a possibilty.
A weak fuel pump is also another possibilty for a falling fuel pressure.