98 PCM on my 01

EllowViper · 06-05-2008, 05:26 PM

Picked up a 98 PCM pretty cheap locally. I didn't really need it but what the heck..the price was right. I know the 2000-2002 PCMs had a few issues with throwing misfire codes due to the fast and unexpected acceleration a ROE introduces into the equation. Different programming design/tolerances from what Sean tells me. Thus far, my stock 01 PCM was working fine (from what I could tell). I put the 98 PCM in the other day and WOW. Talk about a difference. Idle is now right at 14.5-15.5 AFR (I could not get the 01 dialed in at anything other than 12.5-13.5 regardless of individual cylinder trim settings. I had thought the ROE short runner manifold was the primary culpret so I just lived with it...maybe not.) Run-up on boost is instantanious. I thought it good before, but the 98 PCM must have some really different programming. I need to do a bunch of logging, etc to dial this new arrangement in since I doubt my tune is optimized anymore. Anyways, just an interesting observation.

PowerKraus · 06-06-2008, 07:34 AM

Quote:

Originally Posted by EllowViper

Picked up a 98 PCM pretty cheap locally. I didn't really need it but what the heck..the price was right. I know the 2000-2002 PCMs had a few issues with throwing misfire codes due to the fast and unexpected acceleration a ROE introduces into the equation. Different programming design/tolerances from what Sean tells me. Thus far, my stock 01 PCM was working fine (from what I could tell). I put the 98 PCM in the other day and WOW. Talk about a difference. Idle is now right at 14.5-15.5 AFR (I could not get the 01 dialed in at anything other than 12.5-13.5 regardless of individual cylinder trim settings. I had thought the ROE short runner manifold was the primary culpret so I just lived with it...maybe not.) Run-up on boost is instantanious. I thought it good before, but the 98 PCM must have some really different programming. I need to do a bunch of logging, etc to dial this new arrangement in since I doubt my tune is optimized anymore. Anyways, just an interesting observation.

Interesting experience. Are you positive your old PCM had not been flashed by an after market tuner?

Seems the benefits you are seeing would also apply to a 'hot' NA set-up too. Just do what you can to demonstrate/confirm the 2001 pcm was 'stock' and unmolested, and then do the same for the 98....so we KNOW the pcm comparisons are stock to stock. Or do I have this all wrong and the pcm's have been flashed for the roe. Is the roe tune being handled via a vec or other piggyback?

Thanks !

EllowViper · 06-06-2008, 07:57 AM

My 01 PCM was totally stock. No reflash, etc. When I did the ROE with the VEC-II, I was advised at the time to get the earlier PCM due to the "75% likelihood" of having issues with check engine lights due to the programming. I wasn't interested in spending the $500+ at that time for the "chance" I'd have problems..so I waited to see if anything developed. I never did have the check engine light issue and basically forgot about the PCM and tuned away. When this E-BAY deal showed up...I picked up the 98 really cheap figuring I could always unload it for a few $$$. My basic thoughts after driving in this AM was that the accelleration at WOT is a lot more crisp and the transition from vacuum to boost seamless. It does crackle a bit more on decell, but I'm not able to look at my long-term fuel adaptive to see if they are now off from before. I need to plug in the OBD-II logger to see what has changed. I was also thinking that maybe the front 02 sensors are now being viewed differently by the PCM. Not sure the variables introduced by those in the Bellager headers (sensors in the single pipes in #3 & #4 cylinders). But as Martha Stewart would say..."Its all good."

Steve 00RT/10 · 06-06-2008, 08:33 AM

My 01 set some misfires codes last week end. Had never set any codes before. The only thing I can think of which may have prompted this is putting the Quick Fires where they belong..instead of the 3/4 tube set up as it's been since we bought it. Even though I had this running right at WOT, it would still spit black smoke on transition and start up had black soot on the floor. This was due to only sensing the 3rd tubes. The computer could only adjust what it could see.....and it was WAAY fat. After installing the QFs......I checked my adaptives and they were -28%. I dropped the injector set 2% and removed big quantities of cylinder trim fuel as well. No more black smoke, no more soot, clean pipes. The only thing I can think of which may be causing the misfires is that maybe by running leaner, and better, I have now crossed the faster spool up line. Pure conjecture on my part. The plugs are burning great...even the back ones. I'm going to swap out my computers and stick the 96 PCM from the 2000 car in the 2001 car when we take it to St. Ignace in a couple weeks.

May be looking for another PCM myself if that stops the code. The fancy car will only see a couple thousand miles a year, so I may just flop the computers around when we run it on a trip. Around town it's not a real big deal. I was getting a light every 60 miles or so.

How much did you snag the Ebay PCM for?

Steve

EllowViper · 06-07-2008, 05:43 AM

Hey Steve, I'm thinking about the Quick Fires as well since I have the same issue withthe soot, etc. I picked-up the PCM for $140.00 (real cheap for me based on trying to get a few before ...most going for well over 200-300). A guy just a few miles away from work. What do the quick fires run? I hate to call just to ask the price. I have the pigtail extentions already, but my stock 02 sensors would throw the infamous 02 sensor heat malfunction CEL every time when located in the collector.

Steve 00RT/10 · 06-07-2008, 07:07 PM

Hi Eric,

They work. Looks like $205 to here. Your soot could be caused by the 3rd tube deal as well. The pcm can only adapt what it can see. I needed no pigtails. As every Viper is a little different -- be careful that the sensor height is the same. I had this issue before in 2003 with the other car....shorted out. When I recently installed these 2, I shimmed up the little aluminum plate which covers them to gain a little more clearance from the top of the sensor...which was the reason for the earlier failure. The early ones I had in 2003 were slightly longer. These new ones were the same.

Steve