Air to Fuel ratio

[97formws6]

Hello all, I am new to the forum so I thought I would jump right in. I just hooked up an OBDII scanner to my computer and I was wondering if I have any chance of detonation by running the stock 14.7:1 ratio with my mods(97 formula WS6: LT4 hot cam kit, ported heads, long tubes). Also, I am getting a random misfire at idle. I just replaced the plugs and wires, so I know it's not that. Could it be simply because I haven't had the car tuned yet? I have to drive the car about 3 hours to get to someone with LT1 edit, so if there is any chance of detonation I guess I will have to trailer it down there. thanks...

[RAF7789]

fuel injector cleaner, i don't mean to sound like a ***** but check your plug wire locations and make sure all of them are plugged in tightly to the opti and to the plugs. one time, my steering column pulled out 2 of my plug wires when i was driving and boy did i feel like a chump. when i crawled under the car, the wires were gone, and i had to go find them on the street were i came from. Doh! another thing it could be, is what you were saying, the PCM doesn't know whats going on with the camshaft, and why there's so much more flow through the heads. i would suggest getting the PCM tuned. you can ship your entire module to a tuner and he'll tune it, and ship it back, for less than a ben franklin. hope this helps

[97formws6]

I've heard a few horror stories about the "mail in" tuners. A lot of my buddies say that they have never had a computer come back right...they always had to send it back in to get it tweaked a little. Also, the only place I've heard of is pcmforless. I thought they charged about $175. There's a shop in North Carolina that has a pretty good track record. They charge $400 for a complete tune with three dyno runs...the last being a WOT tune. After that, all off dyno tuning is free for the rest of the time I own the car. Sounded like a pretty good deal to me. I'm interested in some other opinions on getting my computer tuned..

[RAF7789]

i looked at the wrong price. MadTuner.com does a full tune for 150, the "budget" tuning is under a hundred.,.

[Injuneer]

Hello all, I am new to the forum so I thought I would jump right in. I just hooked up an OBDII scanner to my computer and I was wondering if I have any chance of detonation by running the stock 14.7:1 ratio with my mods(97 formula WS6: LT4 hot cam kit, ported heads, long tubes). Also, I am getting a random misfire at idle. I just replaced the plugs and wires, so I know it's not that. Could it be simply because I haven't had the car tuned yet? I have to drive the car about 3 hours to get to someone with LT1 edit, so if there is any chance of detonation I guess I will have to trailer it down there. thanks...

Your PCM is programmed to run at 14.7:1 only in "closed loop"----- part throttle/part load condition. It isn't likely that you will get detonation (knock) under those conditions on a stockish, or even heavilly modified engine, unless you "lug" the engine.... heavy throttle at low RPM in the wrong gear. In the event that did happen, the knock sensor would pick up the knock, and the PCM would retard the timing to eliminate the possibility of engine damage.

There's not much you can do in the way of programming for closed loop operation. The 14.7:1 is hard-coded into the programming, and not something you can change with LT1_Edit or other programming software.

When you put the engine under load.... e.g. - wide open throttle..... the PCM is no longer operating at 14.7:1. It shifts to power enrichment (PE) mode operation, and sets a target A/F ratio based on various engine operating data. Typically, the resulting target A/F ratio in PE mode, with stock programming is 11.7:1. And that is "rich". You can pick up 12-15HP simply by leaning out the PE mode tables.

And again, if there is detonation, the knock sensor and knock retard system protects your engine from damage. You would have no risk in driving your car to a dyno for tuning. Your scanner should be able to show you how much knock retard the PCM is using.

With changes including the LT4 HOT cam and ported heads, a small misfire or a code for a misfire might not be all that unusal WITHOUT A TUNE. The PCM uses the crank position sensor to detect misfires. A cam without a tune may produce an irregular velocity pattern on the crank rotation that can show up as a misfire. In any case, you need a tune. Not tuning it can cause misfires.

I didn't see any injectors in your list of mods. Are you still running the stock 24 #/HR injectors?

[97formws6]

Yes, I'm still running the stock injectors. That was the next project, but I thought if I was going to do the injectors, I might as well do the intake...and if I was the intake, I had better put on a 58mm throttle body. I would love to do all of this work, but I don't have the cash. Would just getting bigger injectors give me pretty good improvements?

[1slo_camaro]

i have the same misfire problem with mine is not consistent and only misses when im idling if you find the problem can you give me a shout so i can check and see if that is what is wrong with mine, plugs, wire, and all that is new ive tried all my basic knowledge and cant think of anything else

[97formws6]

i have the same misfire problem with mine is not consistent and only misses when im idling if you find the problem can you give me a shout so i can check and see if that is what is wrong with mine, plugs, wire, and all that is new ive tried all my basic knowledge and cant think of anything else

I'll definately let you know when and if I figure it out.

[97formws6]

OK..I think I'm going to go with bigger injectors. My only unknown is: If I put on bigger injectors, can I run the car without a tune with no damage?. I'm looking at the Accels on Summit. Probably the 36#. I know very little about injectors, so any input would be great. Like I said, my biggest concern is engine damage running the bigger injectors without a tune...as I have to drive the car a considerable amount for a tune. I've searched the forums for this info, but can't find it.

[1slo_camaro]

as far as i know the computer will regulate the a/f ratio so it shouldnt mess it up its not like carburated where you have to set the a/f ratio yourself now a days we have damn computers to do it for us. so it should regulate the air (MAF) and the fuel pump to pump the right amount of fuel. MSD has coils and ive ran msd my whole life all from 4 cyl wrxs and geo trackers to 800hp BBC so i think highly of MSD ive had problems with accel. well good luck with your ride

[Injuneer]

OK..I think I'm going to go with bigger injectors. My only unknown is: If I put on bigger injectors, can I run the car without a tune with no damage?. I'm looking at the Accels on Summit. Probably the 36#. I know very little about injectors, so any input would be great. Like I said, my biggest concern is engine damage running the bigger injectors without a tune...as I have to drive the car a considerable amount for a tune. I've searched the forums for this info, but can't find it.

You can not install larger injectors until you have the correct injector flow rate programmed into the PCM. It would be flowing 63% excess fuel with a 36# injector on a 22# program. The long term fuel corrections can only remove 15% excess fuel. At WOT, you would still see 63% excess fuel. That much fuel can do serious damage to the engine, in a short period of time.

That was the next project, but I thought if I was going to do the injectors, I might as well do the intake...and if I was the intake, I had better put on a 58mm throttle body.

You don't need a new intake manifold, and you don't need a 58mm throttle body.... save your money, and spend it on useful mods. Don't just start replacing parts that you don't need. I have a 58mm TB on an engine making 500HP without the nitrous. It is overkill on my engine. During engine dyno tuning, we were able to measure the actual air flow to the engine, and a 52mm TB would have been able to meet the engine's air requirements. The stock LT1 intake is more than adequate for the setup you have. If you have some really healthy ported heads, the intake should have been ported and touched up to match the heads already. If not, that's all that needs to be done, not a new intake.

[RAF7789]

...overkill...

true, GM used the same 48mm throttle body on on the LT1 as on the 502ci BB!!!!

[Injuneer]

Do NOT buy Accel injectors. In all the forums I cover, they appear to be nothing but problems. Everyone complains about them.

You keep your larger injectors in the boxes. You drive to the location where they are going to tune the car. While the tuner is loading the initial program into the PCM - including the new flow constant and offsets for the injectors - you swap out the injectors. There is no need to drive the car with large injectors on a stock program.

[Rob]

Its showing misfires because you are running the stock tune. It is also probably extremely lean at WOT. I know when I put my HOT cam in my 96 WS6. That is what happened. It was even rocking on the dyno because it was so lean.

I ran the stock injectors in mine but didn't spray. That would be the only reason to upgrade injectors.

Get a tune and it will run a lot better. It will throw no codes and you'll be a lot happier