PistonHead

Hopefully I can make this as easy to read as possible.

I'll give the history of the car up to this point.

'94 Caprice
383ci LT1, GM846 cam, 58mm BBK TB,
Nitro Dave's 58mm plate kit, Mallory ignition, MSD coil,
Clear Image Tri-Y coated headers, high flow cats, 2 1/2" full mandrell bent exhaust,

Front four cylinders run very lean at idle.

Rear four cylinders are rich at idle.

Engine temp runs to hot at idle or even on the highway. (back when it was actually driveable)

Car starts and runs very good initially. At about 4 minutes the cats start to glow and by 8 - 10 minutes some header primaries are glowing as well as everything back to the tailpipes. (cats, x-pipe, tubes up to the mufflers...)

The car is no longer driveable. Everything starts smoking and burning after the 10 minute mark.

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I've gone over and over looking for vacuum leaks and have not found any.

removed intake and inspected the IAC passages. All clear and good. replaced gaskets and re-installed intake. No change.

Swapped injectors front to back and then replaced all of them with a temporary set to test. (running 30lb SVO's) No change.

IAC and TPS are both within factory specs.

Replaced fuel pressure regulator with an Aeromotive adjustable and have it set to stock pressure. No change.

Replaced the PCM after it stopped responding while running. no change.

Verified spark at each plug.

Removed Autolite 103's and swapped back to stock plugs with stock gap. No change.

Replaced the SLP shorties and factory cats with Tri-y headers and high flow cats. No change.

tried running in both open loop and closed loop. Makes no difference.

By-passed the Mallory 685 ignition and then eliminated it. No change.

Checked and re-done valve lash.

I have verified that the actual timing that the car is commanding is what it is getting. As far as what TDC #1 is compared to what my laptop shows.

Compression test on engine shows lowest is 205 to highest at 215psi.

Cats have been replaced. No change.

Wideband A/F ratio shows around the 14 and change mark at idle. Verified readings with a second wideband.

I have used two separate well respected mail order tuners with no difference in the way the car behaves.

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The car's been stuck in the garage and not driveable for a long time now. I finally found a shop to work on it, but they are a little stumped right now as well.

After spending a few hours trouble shooting the car, the shop is leaning towards something in the tune causing the issue.

Therefore:

By making individual cylinder adjustments they have been able to get the car to run much better. They have added fuel to each of the front four cylinders until the car no longer turns anything orange at idle. The down side is that the car is now running at 12 and change at idle. It likes the extra fuel, but this just seems like a band aid and it won't pass emissions running like this.

I'm a little worried that adjusting the front four cylinders is possibly masking the actual problem. Whatever it might be.

The car still slightly turns one cat orange while driving, but after stopping and idling, the orange will dissappear. The car's fans cycle off and on now at idle. Before, once they turned on the car would not cool down enough for them to shut off.

I'm sure I've missed a few things I've done. It's been a real nightmare for quite a while now. Being completely out of ideas myself, I've turned to this shop and they are kinda stumped now as well.

Any idea's would be greatly appreciated.

Thanks,
Brad

jaycenk

iTrader: (1)

what was your idle like before you made changes to correct the front cylinders in the tune? Have you checked the TB to make sure it isn't leaking either at the IAC or gasket or at the body its self (cracked)? Have you check for un metered air leak behind the MAFS? Double check an conections past the MAFS. Have you verified the PCM is good by using a dfferent PCM from one of the tuners? Are the injector plugs them selves good? this can cause real bad odd ball problems. Other than that make sure if the PCM has been removed that you don't have a bent pin.

jaycenk

iTrader: (1)

Oh yea whats the fuel pressure set at?

PistonHead

Before making adjustments to the front cylinders the car idled perfect. If everything didn't start to glow orange, you'd never know that there was a problem.

I've had the TB off a few times and looked it all over. New gaskets and everything. Nothing I can find to indicate a possible leak.

My MAF connects with a single coupler to the front of the TB. I've gone over both clamps and the sensor connections and found nothing.

Here's a picture to show the MAF location:



I am now on my second PCM. The first one was working up until two weeks ago. After it stopped responding I replaced it with a new one from the dealer. We switched back to a tune before we made adjustments to the front cylinders (thought we had found the issue) and it made no change.

I ran a noid light on each injector plug and looked at the connections. No signs of heat, melting or corrosion at the time. I will double check this again, next time I am at the shop.

I'll check the pins on the PCM next time I get to the shop.

Fuel pressure if I remember is set to 44psi. I have a walboro 255 in the car and it was causing the factory FPR to sit at 56psi. Upon discovering that I thought I had found the issue. I replaced the OEM one with an Aeromotive one that was able to set at the correct pressure. Again it made no change. Hell, I even tried dropping pressure down to 30psi just to see what happened and at idle it didn't change anything. re-adjusted it back to factory and continued on ...

Thanks,
Brad

jaycenk

iTrader: (1)

Your still running the steam pipe on the back side of the heads?

PistonHead

Yes the steam pipe is still installed.

Thanks,
Brad

DisturbedTA

iTrader: (3)

did you chedk the wiring to the injectors ive had this problem before with a mustang i had the wrong cam,firing order was for a ho and my cam was a regular 302 firing order all my stuff glowed untill i changed the spark plug wires around i know thats was a ford not a lt1 i just giving you ideas

PistonHead

I musta gone over the plug wires a dozen times. Seems to be a common problem.

My plug wire order has been verified by a couple people.

As for the injector wires. They are numbered on the plug so I have verified that they are on the correct injector.

Thanks,
Brad

DisturbedTA

iTrader: (3)

ok kool um gm never did any different firing orders right? oh are your mufflers on? i see you changed everything but those

PistonHead

I don't believe they did any other firing orders?

I've had 3" exhaust with SLP shorty headers and factory cats. Then swapped the cats for export pipes. Using Dynomax Race magnum mufflers.

Then I went with open headers, which the O2 sensors did not like.

Then new Tri-Y headers and high flow cats.

Then I added an X-pipe to the cats.

Then I put on the rest of the system using magnaflow mufflers. 2 1/2" all the way this time.

Through all of that it never made any difference. Whatever pipes where on the car would get orange.

Thanks,
Brad

fuel

iTrader: (13)

if you have a lazor temp gun you can tell what the temp is on the front 2 and the back 2.

i had i problem like that to,fronts running lean and backs fouling out.i was chasing a ghost.i changed to a vic and problem solved......i just put my budy's 396 to gether and

he have the same problem.lean in the frount rich in the back.car sounds awsome at start up,and after 2 minutes starts to sound like crap.he has not got it tuned yet to see if it cand be fixed.

fuel

iTrader: (13)

with a lt1 computer can you and more fuel to the front 4 cylinders at idle or lean out the back 4.

PistonHead

I've used a laser temp gun on the header primaries right at the port. There is over 200deg difference from the front tubes to the rear tubes.

The shop that has it now is actually using a temp gun as a method of checking the results of adding fuel to the lean cylinders.

They have kept adding fuel to each individual cylinder until the temperatures of each tube are similar. This is how they got it to be able to run so much better.

The front four cylinders are now being given more fuel, which has lowered their respective primary tube temperature significantly. The car was able to be driven and idled for a long time in the shop, but it is now running at 12:1 at idle.

Keep me posted on the 396 tune. I'd be really interested in seeing how it gets worked out.

Thanks,
Brad

fuel

iTrader: (13)

i was getting i think 480 to 500 degree on the fronts and 290 on the rears.the backs are to cold and the fronts are to hot.and it is to hard to get a good reading on the middle two i think because thay are so close that they effect each other.

fuel

iTrader: (13)

did you at all grind out the hole front of the intake like this

PistonHead

Sounds like the exact same issue I am having. The temperature numbers even sound similar.

I had the intake machined to match my 58mm TB, which left a ridge on the outside top of each bore as well as on the bottom centre. I ground them down as much as possible to smooth the transition into the intake.

As you can see from the pictures I did keep that centre port.





So you changed to another intake manifold, which fixed the problem?

Thanks,
Brad

RamAir95TA

iTrader: (2)

Do you have stock 94+ fuel rails, regulator, etc.?

PistonHead

Stock fuel rail with an Aeromotive adjustable fuel pressure regulator and Ford 30lb SVO injectors.
All supplied by a Walboro 255 pump using the Racetronix wiring kit.

Thanks,
Brad

PistonHead

Still trouble shooting. None of the suggestions panned out.

Any other experience / suggestions ?

Thanks,
Brad

Wicked94Z

iTrader: (26)

email me a copy of your tune.

wicked94z@aol.com