1994 LT1 tuning Issue

[roughneck427]

Heres the tune that was in my car back in 2006 it was a 95 LT1 6 speed 355 ported heads with a GM847 cam that cam is somewhat close I did have 36LB injectors in it so if you try it you will need to rescale it and cyl volume changed for the 355.The car put down 391 rwhp on a dynojet through mac mid tubes.

[steveo]

you have to wonder how much that has to do with the difficulties in nailing closed loop idle on this platform. the system starts kicking the crap out of each other pretty fast.

you have a cam with a bunch of surge, so you have fluttery MAP, your FPR fluctuates pressure, but the random waveform of afr alterations that produces doesn't really correspond to anything useful. then, every tiny change in afr that corrcl and int are making, the fpr is making its own jitter and confusing the hell out of it.

perhaps that's why when i was doing some just for fun 'how low can i go' idle testing, it would idle around 400rpm no problemo if i put a restrictor in the vac line to slow down the fluctuations, but without the restrictor it would almost die. i'm a bit different, though, my cam makes fairly high idle but unstable idle vacuum. unfortunately i couldn't leave it like that, it noticeably affected throttle response. instead of a blip of throttle instantly maxing out the FPR, it would lean out for a split second.

[Caleditor]

you have to wonder how much that has to do with the difficulties in nailing closed loop idle on this platform. the system starts kicking the crap out of each other pretty fast.

you have a cam with a bunch of surge, so you have fluttery MAP, your FPR fluctuates pressure, but the random waveform of afr alterations that produces doesn't really correspond to anything useful. then, every tiny change in afr that corrcl and int are making, the fpr is making its own jitter and confusing the hell out of it.

perhaps that's why when i was doing some just for fun 'how low can i go' idle testing, it would idle around 400rpm no problemo if i put a restrictor in the vac line to slow down the fluctuations, but without the restrictor it would almost die. i'm a bit different, though, my cam makes fairly high idle but unstable idle vacuum. unfortunately i couldn't leave it like that, it noticeably affected throttle response. instead of a blip of throttle instantly maxing out the FPR, it would lean out for a split second.

I am just trying to tune the VE tables in Open Loop. It just seemed like I was pulling way too much from the VE table. I had a correction factor of 20 to 30%, so I chopped it by 25% (The AFR was in the high 10's to mid 11's). Then I logged it and had a correction of .7 to .835 (AFR of 11.1 to 12.8). I another 25% and it was still rich
The cuts were across the board and figured I would go back and add if I needed to
I stopped

[EagleMark]

I checked the fuel pressure. The engine was cold, so it did not have much vacuum

@ idle I had 41 psi. I am thinking is was 9" or less
@ 2000 I had 36 psi. The engine was smooth, so it should have been around 18". This is whatI had on previous data-logs

Since this calibration has 1 injector setting for flow rate I can see how this could be compounding my issue. Later calibrations have a table for Flow Rate Vs KPA

KOEO was 41psi, but I did not check it after I ran the car. I thought it might be on the low side, so I headed in to check the spec.

I will go ahead and proceed with my tuning method.

Well the pressure will be higher with engine running do to altenator charging, higher voltage in system to pump = higher pressure.

Found this from a reliable source:

Put the pressure gauge on it, start it up and let it idle. Remove the vacuum compensation line from the fuel pressure regulator (cover the end of the line so there's no vacuum leak). Fuel pressure without the vacuum line should be 43.5psi. Factory specs are 41-47psi.

Reconnect the vacuum line, and the fuel pressure should drop in proportion to intake manifold vacuum. With a stock cam, a drop of 6-8psi from the "no vacuum" pressure is normal. With the HOT cam it might only drop 5psi. So, 35psi at idle, with the vacuum line on may be almost "normal".

Tape the gauge to the window, and take it out on the road. Run it up to max load/RPM. The fuel pressure should stay at 40psi or higher. Anything less and the pump is weak.

And when your all done and do the WOT high RPM with that cam I still say your going to go lean with stock injectors, pump and wiring to fuel pump.

[Caleditor]

Well the pressure will be higher with engine running do to altenator charging, higher voltage in system to pump = higher pressure.

Found this from a reliable source:


And when your all done and do the WOT high RPM with that cam I still say your going to go lean with stock injectors, pump and wiring to fuel pump.

That may be the case, but I am not that far into the tune. If I was lean I would be happy, then I would look at it differently.
So far on this log I have a cell that is 40% tooooooo rich. This long hand math is for the birds.

The voltage will not change the pressure in the rail. The regulator dumps pressure

[lionelhutz]

The idle fuel pressure at 41psi seems too high. Even if the vacuum numbers you listed are correct it should have been around 38psi or 39psi.

Having to cut that much fuel just doesn't make sense.

Are you sure the injectors are 24lb/hr units and not something else? Have you put a wideband on each bank? Checked the plugs? Done anything to confirm all cylinders are running about equal for AFR? Checked that all cylinders are firing? Checked that all cylinders have compression?

[Caleditor]

The idle fuel pressure at 41psi seems too high. Even if the vacuum numbers you listed are correct it should have been around 38psi or 39psi.

Having to cut that much fuel just doesn't make sense.

Are you sure the injectors are 24lb/hr units and not something else? Have you put a wideband on each bank? Checked the plugs? Done anything to confirm all cylinders are running about equal for AFR? Checked that all cylinders are firing? Checked that all cylinders have compression?

Stock Injectors.

Heintz Racing did the work.


if I have to pull the plugs the car won't get tuned. I will cut my loss and give it back.


I work at a dealership from 7 to 5. I have been a driveability tech most of my life. I started out doing it and with fuel injection I needed to do other types of repairs

[Caleditor]

Sorry if I have been short with some comments, but I have been doing the VE table in long hand for the last 2 hours.

[EagleMark]

Very rarely do I get a built motor, transplant or even bolt on mod tune on a daily driver and not find some kind of maintenance, mechanical/wiring issue... very rarely! My diagnostic skills have increased ten fold when my tuning skills were up to par. I still learn each and every car and each and every day here helping others.

[lionelhutz]

Heintz Racing did the work.

Seems to me if they did a good job you wouldn't be trying to get it running right.

Were you told they are stock injectors or did you pull an injector and check the part number? If I've learned anything troubleshooting it's don't take anyone else's word for what they've already checked and confirmed is OK.

[EagleMark]

if I have to pull the plugs the car won't get tuned. I will cut my loss and give it back.

Quick and easy test but not all inclusive... gives you direction if there is a spark issue.

Use an infrared heat gun on each header tube when warmed up and cleared out and see if all cylinders are close to each other. If not, well there's an issue going out the exhaust and skewing the WB or NB readings.

[dave w]

I'm often challenged with injector flow settings. Rated injector flow rate / actual injector flow rate / programmed injector flow rate in the .bin are not always the same value.

I think I would change the injector flow rating, for a rich running engine I would change the injector flow programmed in the .bin to a larger flow rate to lean the engine.

The attached .zip file is an excel spreadsheet I did for $EE VE tuning using TunerPro RT.

dave w

[Caleditor]

I checked the numbers on the injectors

I would not say that it runs that bad at all. It has a poor idle, but I expect that

I am attempting to correct the calibration as I would on any other tune.

I have a step by step process and I am simply stuck on the VE table. Even if stoich is 14.1 and I am doing the math at 14.7 then I should be lean and I can not get it lean in the majority of the cells. I had it lean in 2 cells last night

[Caleditor]

I'm often challenged with injector flow settings. Rated injector flow rate / actual injector flow rate / programmed injector flow rate in the .bin are not always the same value.

I think I would change the injector flow rating, for a rich running engine I would change the injector flow programmed in the .bin to a larger flow rate to lean the engine.

The attached .zip file is an excel spreadsheet I did for $EE VE tuning using TunerPro RT.

dave w

I will try this after I do the Open Loop VE tune.

[Caleditor]

I am just trying to tune the VE tables in Open Loop. It just seemed like I was pulling way too much from the VE table. I had a correction factor of 20 to 30%, so I chopped it by 25% (The AFR was in the high 10's to mid 11's). Then I logged it and had a correction of .7 to .835 (AFR of 11.1 to 12.8). I another 25% and it was still rich
The cuts were across the board and figured I would go back and add if I needed to
I stopped

I chopped the VE table up last night and fired it up. It cranked, fired, stalled several times. I got it running but it was tooooooo rich and eventually stalled. I went in and looked over my changes. I am pulling fuel not adding, so it is a little confusing. I smoothed the VE table slightly and removed some of my correction.

I flashed it the morning and it never even started.
I flashed in the Mod tune and it would not start. I could not get it to fire off in clear flood mode. I pulled 1 plug and found it slightly wet.

I got a ride to work.


This car is not that nice. First it's OBD1, Second the owner was not a car guy. The car has a unsprung puck clutch. The trans is about to grenade. The rear end whines. The exhaust was banging on the floor. I replaced the engine mounts to correct the exhaust issue. The O2's were weak. Installed 2 used O2's from an upgrade I did. The heater did not work when I got the car. It had an air pocket in the heater core. The electric water pump has a drop of coolant on it. The drivers window is inop at times. The drivers door lock is inop most of the time by remote or key. The tires are on the wear bars. The engine oil pressure drops very low at times. It will be Ok one test drive and the next time it will be close to 0 at idle. Cold start it might be over 1/2 way and the next morning it might be 1/8 off 0.

The car runs good. It does not misfire. It has a mild surge at times in gear at cruise at lower RPM's. Long tubes with the old style O2's cause this.

The car runs smooth, but I have not been able to OLSD tune it

I will load TunerPro back on the dealerships laptop and look for something that is effecting my fuel in OPEN LOOP