Truck is stock. Installed a 180 t-stat. Plenum fix parts in the mail (so not fixed yet). Tuned the truck w/ the 87 tune. Idle became very rough, no audible pinging. Letting off the brake at idle lead to heavy lurching in sync with the lobing of the engine. Two days later started throwing P0305, Cyl 5 Misfire. Cleared code. 12 hrs later same thing, and then it happened again less than 5 min. Restored to stock. Idle is no longer rough, lurching gone. Not run long enough to see if it will throw the code again. Interedting bit is that it was only Cyl 5 missing. Is this because of the broken plenum you think?

 

Need to eliminate that as a possibility. The tune relies on the engine functioning "normally" I.E. No major vacuum leaks......

 

Might also check plug wires/wire routing while you're at it. Cylinders 5 and 7 are especially prone to misfire due to arc. Don't think there is anything in the tune specifically that would cause it, but I'm not familiar with all the parameters that can be adjusted by SCT.

Look for pretty blue lights on the wires at night, but don't try to touch them.

 

What year is the truck?

 

truck is an 01 with the 5.9. seems like the truck still idles kinda rough. when you tap the gas from a dead stop, anything under 10 mph is lurchy. idk if its the engine idling rough or if the trans is slipping but i dont think its the trans because it is a rebuild with less than 15k since install. Going to check all fluid levels now...

 

If you paid for custom tuning, ask your tuner to send you a tune with torque management left ON.

The the SCT tune runs much better, you can then safely blame the trans/torque converter.

 

I put a SCT in a friends truck and had some of the same symptoms. The only thing I could think is he never had a flash done. We didnt investigate so who really knows. He still drives the truck stock with no issues.

 

No way. If it was a mechanical failure such as a vac leak, it would have been persistent regardless of the tune and, it most certainly would not be isolated to CYL 5 either. There's either an issue with the tune itself that's the root problem or, there's something out already with the EFI system whereas, it is possible that it had a pre-existing condition such as a possible injector related issue which, could be a fault in the driver CKT for that injector etc. But, if that was the case, it would have run rough 100%- not just on the new tune.

To me, the way that you described the problem, (ran fine before tune, ran rough after STC tune, ran fine after returning to OEM) this leads me to believe that the root of the issue is rooted at the STC tune. PM Hemi and have him go through it to rule that out before doing anything to your truck. Start there first.

Has it been rough PRIOR to installing the tune? If so, it's most likely a pre-existing condition that is exacerbated by the new tune.

Did you clear out the memory AFTER installing the tune? I have had some quirks after a flash (DID NOT clear memory) and, what I do to alleviate that is to simply disconnect the negative terminal on the battery and wait about a minute just to make sure that all power is drained from the caps in the PCM.

What happens is, it retains some of the old parameters that are in memory at the PCM level thus interfering with the new flash. Try resetting the PCM by removing power for a minute or two. Contrary to what ANYONE tells you, NEVER ground out the NEG to the POS battery cable on a PCM.

Here's why: if the caps are charged up to full capacity at the cap level, the discharge is violent enough to induce failure at the PCM level. It is VERY hard on the caps to fully discharge them instantly and, if that is done repeatedly, damage to the inside of the caps is imminent. This is also why it sparks when discharging them in this manner. It also increases the chances of a back-feed voltage spike through case ground- not good as all the sensitive components as well as the high current / voltage component legs are tied to ground thus blowing the gates and drains on the ICs to blowing FETs, Diodes and various other components.

IF, you want to expedite the discharge rate, YOU MUST place a 1M resistor in between the leads. This will perform a safe, soft discharge that is safer and won't induce a latent field failure later on down the road.

CM

 

I'm just thinking out loud, but if he has not replaced his Plenum gasket yet that definitely could cause you to have a huge vacuum leak. After I installed the SCT Tuner mine ran like night and day. It got rid of all the death/flash issues I was having and everything.

 

True, but, <IF> he had a HUGE vac leak, it would induce a lean running condition on ALL cylinders- not just CYL 5 as was stated. If and when there's a plenum leak that is bad enough, there will be signs of oil fouling out the plugs.

This will occur on all tunes across the board. The vacuum leak will also induce pinging and show signs of detonation but, it's not going to be isolated to just one CYL as it's the common air intake for all cylinders.

So, if it's pinging on an OEM tune, it would ping and detonate on any tune as it's a mechanical malfunction that is common to all. It should also be noted that no pinging was audible / noted during this rough-running condition. The common function is: A/F ratio. ON any tune, this ratio is to be established and remain constant. With a HUGE vacuum leak, it's not going to remain constant. As a result, it will keep moving around as the load and idle speeds change. It would also induce a high idle condition, a loping idle condition, a lean running condition on all cylinders thus leaning the fuel mixture out. This would be common to all cylinders as they all share the same intake supply so, theoretically / logically speaking, they all would use this unmonitored air during the intake stroke as, again, it's one intake that feeds all eight cylinders.

What was mentioned was how it was fine after returning to OEM stock. When the problem was resolved, I noted a change was made- return to stock OEM tune. Therefore, it my belief that this is not a mechanical failure relating to a large vacuum leak at the plenum for, if it were, it would continue to induce failure across the board on not only the STC tune but, the OEM tune as well.

To me, when reading through the original posters first post, it almost sounds as if the sync value / EFI timing is out of whack. Lurching is sometimes associated with a timing issue. Without seeing the PCM parameters on the screen and watching the timing on a scope, one would be hard pressed to come up with a definitive answer as to what the root cause is.

CM