DieL

Im going to be installing a DFI very soon for my new stroker. Im curious about trouble codes showing up. Someone says to just unplug the bulb but it sounds like a band-aid fix. i would like to have the fans turn on sooner, and desensitize the knock sensors a bit if possible.

TIA. :cheers:

tjwong

Why go thru the trouble and headache and expense of installing a DFI system. If you have a OBD1 or a OBD2 PCM it will control all but the wildest stroker motors one can want to drive as a daily driver. LJ Stevens runs a 9 sec LT1 engine using the stock GM PCM in his F body.

Properly tuned a GM PCM will give you better drivabilty and more precise control than a DFI system can. Plus the cost alone should a DFI ECM fail would scare me off. At $100 or around that one can replace a GM PCM.

DieL

I hear you perfectly, and you are correct as well. The only problem i have is that the stock computer will shut down at 7000, or is it 7200 rpm. the stroker i built will redline 7600. And thats why i had no choice.

From what i know the dfi is a piggyback system so the stock computer may show codes... i just wanted to eliminate knock codes, egr and get the fans to come on sooner.

I guess i just send my chip out to someone?? :cheers:

snaketr

I have DFI. It will control more than the stock one PCM, however buy LT1 edit and you can change where the redline is set.

tjwong

Yes if you piggy back a system on top of the OEM PCM it will show codes. Especially if you disconnect the sensors and solenoids and such. I have a way to disable most any code within the GM PCM. But I need to know what you are disconnecting to be sure I get them all.

I can understand building a engine to handle 7600 RPM but would you really need to rev it that high? Mine ins built to do that as well but it hardly ever sees 6500 let alone 7600. I have heard that the GM PCMs will only go to 7000 or 7200 but I have not heard what happens if the RPM exceeds that. I have heard that the PE tables just straight lines from the last entry and that is it but the engine keeps running. But I can't confirm that.

Also if you disable the PCM your ASR and anti-lock brakes may not work correctly.

DieL

thx for the help. I honestly dont know what exactly will be disconnected, if anything is. Im still debating on blocking the egr at the back of the LT4 intake so i know i might need the egr removed... if possible.

The shoppe has had stock pcm cars - namely a friends canfield headed 95 that revves to redline. At 7200 the motor just shuts off. This happened a few times on the highway. My motor is a solid roller and has been specced out to make peak power around 6800 so it should still make huge power till 7600. Its more of a highway missile :D .. gotta teach those vipers and bikes.. :D

- i dont think the stock pcm will be disbled at all. And on top of that were trying to get this puppy to pass emissions.. cats and all.. the car should be dropped off in a week to start the dfi install so i can keep you posted if possible. I really appreciate any help you have given me. So i take it you can burn me a chip when i need or know someone who can?? I know i did buy some of those rewriteable proms, like 4 of them a while back when i thought i was going to use the stock computer... maybe i could use those??

TIA :) :cheers:

tjwong

Actually there are no proms in the OBD1/2 PCMs. There are two flash memory chips that are soldered onto the two main PCBs inside your PCM. And you are right the PCM will crash at 7200 RPM, then the ignition has to be shut off so that it can reset before the engine can restart.

Deleting the EGR codes would be a piece of cake. What would need to be done is that you send someone or me your PCM to have the programming done. I use a bench harness to do this with the PCM connected to my desktop or laptop PC. Keep us informed on your project, and I agree the bikes and vipers do need a spanking at times.

My engine is a supercharged 396, I am not using a solid roller in my engine. I do have a decent custom ground Comp cam which is still pretty streetable yet one can still hear a decent thump at idle. I maintained the GM PCM for practicality and ease of tuning. For street use I have found DFI and FAST systems to be a bit finicky. One has to spend a lot of time tuning to get them right for every day drivers. Especially when the engines have big cams in them.

And I have found most to have the need to be retuned if one goes to an high altitude situation. I have heard that the new DFI GEN7 has corrected this but I don't have any personal experience with them, I have done a few FAST or what used to be SPEED PRO systems, and with them even with the wide band o2 option they had to be retuned for high altitude operation.

I have found that for most situations one can't beat the control of a GM PCM. Even when the engine has cams in the 240 degree range. The only drawback is this 7000 RPM limit, which cannot be programmed out as it is hard encoded into the firmware.

DieL

how about the knock sensors, can they be desensitized?? Can you or do you know anyone who can burn this stuff for me?? i have removeable prom chips so i can send them.. theyre the re-burnable ones.

tia :cheers:

tjwong

The knock sensors can be mechanically desensitized by wrapping teflon tape around the threads and torqued to 11Ft/lbs. Or they can be disabled via PCM programming. You mentioned you have removable proms? What is the PCM service number? It should be a 16181333 if it is a 94/95 vette.

Oh by the way there is an Opti Spark conversion to coil over plug ignition that give you 8000 RPM potential from a GM PCM control. It is called a LTCC conversion which installs 8 coil paks from a LS1 engine onto the LT1 engine. It takes the high voltage side of the Opti away from it and channels all the spark energy from 8 coil paks just like a LS1 engine. The story is that it extends the RPM range to 8000 RPM. I haven't seen this personally but that is the story I am hearing. So if this is true this could be an alternative to going with a DFI or a FAST system and would save you hundreds of dollars!


[Modified by tjwong, 11:46 PM 8/21/2003]

DieL

i heard about the system a little too late (the coil/cyl one).

The car is a 93. I have reburnable chips for it. THeres a custom one in it now but i bought some extras (4).

tjwong

Actually you have an early LT1 with a pre-OBD1 ECM. 94/95 was actually the begining of the OBD* series PCMs with on board diagnostics. I can't say for sure what the RPM limit of your ECM is. Have you actually tried going over 7200 with your present stock setup? I checked in my tuning programmer for your ECM and the spark tables go to 7500 RPM while the VE Maps run up to 7000 RPM. And the PE tables go up to 7500 RPM as well. Your ECM maybe capable of running to 7500 or higher.

While it is true that for sure OBD1 (16181333 and 16188051) PCMs do take a dump at 7200 RPM I can't vouch for an earlier ECM style or what has been done with the firmware in a OBD2 (LS1) style ECM.