LT1 going lean

[LT1Nova]

After blowing a head gasket 2 years ago I tore down my LT1 and made some changes to the fuel system when putting it back together. I discovered a problem when I finally got it back to a driveable condition this fall. The car has -6 braided hose to and from the engine bay. I had -8 fittings welded to my fuel rails. I adapted up from -6 to -8 in the engine compartment on the supply side. On the return I ran -8 to the Aeromotive 13301 universal regulator and left the -6 to the tank. Fuel pressure was set at 46.5 at idle with the vacuum hose removed. I have a wideband A/F gauge in the car and it shows it going lean at higher RPMs and it starts popping at about 3500-4000 when easing on the throttle. If I stab the gas when at a lower RPM when driving it will also pop. A/F ratio when cruising is about 15:1. The in tank pump is a Holley 225 lph unit in a Rock Valley tank. Also if I turn the key on and do not start it the fuel pressure will drop to 10 psi within a couple minutes. Anyone have any ideas? I have double checked the spark plug wire routing to make sure I didn't have any going to the wrong cylinders.

[DeltaT]

I would start with a pump volume check. In the engine compartment, remove a supply side hose and connect another hose to it so you can safely pump fuel into a container outside the car. Since you have a 225lph pump, if you remove a pre-regulator hose and test that way you should easily be able to pump a gallon in about a minute.

You may find that the fuel pump shuts off after a short time when you just turn the key on but don't start the car. This is pretty normal - they just want to pressurize the system but not have the pump on full time for no reason. If that's the case you will have to hotwire the pump to make it run.

If the test is successful, then try the same test on the return line from the regulator, either in the engine compartment or at the tank.

Having -8 in your engine compartment pretty much means nothing. The -6 to the engine is the gating diameter, but it should be fine for your application.

A common problem I see is poor wiring for the fuel pump - wires not a heavy enough gauge (on the + or on the ground sides, equally important), poor connections, etc. Worth checking.

Where's your filter(s) in all of this?

Let us know how it works out and we'll see what the next clues are.

Jim

[LT1Nova]

The day after I wrote that it dropped into the teens and twenties and snowed here. Also my garage is unfinished and I don't want to drive the car now to test it so I'm not sure when I'll get out there to check on the suggestions. It may be a ground wire issue as I was having issue with the fuel level gauge as well. Thanks for your suggestions, I will try to remember to post my findings.

[avewhtboy]

We used to tape a mechanical fuel pressure gauge to the windshield of the car and make a few test runs.

It really helps to determine where the problem is before you start
reworking things.

It could be in the tune, have you loaded another tune into the pcm to see if the problem still exists?

I would start there before I spent money reworking anything, although it sounds like you can not drive the car now because of snow???

I don't see how you guys up north stand it!!!

[MonzaRacer]

OK first of all your fuel pressure is dropping because of no check valve or a bad one and unfortunately till you fix that issue, your gonna have issues.
Also the pump may not be big enough in one way yet big enough the other.

[MrForce]

What size (flow rate) and how old are the injectors. They tend to gum up when siting for a long time.

[LT1Nova]

I was kind of guessing there might have been some sort of check valve in the stock regulator that is not in the aeromotive. The injectors are stock, 28# I think. I was thinking on trying some FI cleaner since it hadn't been run in a while. I don't think it's a fuel pump issue, it's a 255 LPH Holley in tank. Yeah I know they can go bad but it doesn't have that many miles on it.
I have a fuel pressure and air/fuel gauge in the dash so no need to tape one to the windshield. I do not recall it loosing pressure, just the going lean. It is a non stock tune which I was going to try reloading at some point just to make sure that was not it. It will probably be April before I get it out to test drive again between the snow and the salt on the roads.

[LT1Nova]

I was looking on camaro site and found the post below. Aeromotive offers a replacement diaphram for under $20 so I'm going to try this first once Spring, nice weather and clear roads show up

Copied text:
"Wanted to post and let everyone know of another example of an Aeromotive fuel pressure regulator going bad.

I maybe had 4,000 miles on this regulator and it's bad. The car wouldn't hold fuel pressure, it would bleed off and it was going lean in the high RPM's. Swapped out for a GM Fuel Pressure Regulator and all issues are gone."

[LT1Nova]

I swapped out the fuel pressure regulator diaphragm and fuel filter and took the car for another drive. On this drive I noticed that the light for the Innovate LM1 O2 sender was shutting off when the car started missing. I found a loose ground wire and it fixed most of the problem. I still have a slight miss occasionally at high rpm but the A/F ratio stays about 14.7 and the pressure does what it should. I did find out from Aeromotive that my FPR is not designed to hold pressure when the pump isn't running so everything works as it should there.

I am going to run some injector cleaner through it and put some miles on it to see if that helps the remaining issue since it's been almost two years since it's been driven much.

Thanks for everyone's advice.

[Randy67]

My 95 TA had a high rpm miss when I got it (used from CarMax). After a trip to the dealer, it turned out the coil wire was corroding at the coil connection. New wire and cleaned the coil terminal, ran like a champ. I was reminded of this when doing the LT1 swap into my El Camino as the coil had the corrosion on the coil terminal as well. Just something to check as well.