Is this LIMP?

[Boost]

An agressive tune in an '05. It has been running well and very powerful, but he rarely steps on it. Recently, after stepping on it hard, it banged into a bad shift, then would not upshift and felt very bad "as if it ran out of fuel". After cycling the key, resumed normal operation. Clearly, I have to go in and reduce the tune, and scan for codes and log data. I asked in another thread what PIDs I should log. Trans. wise:

What codes should I look for? Could this be limp mode? Are there different versions / symptoms of limp? Could it be because he never fully steps on it so the TAPS never got a chance to adapt? In any case if it slips or limps it's no good.

I thought the "PRNDL" would flash and then it would set a code in typical limp... are there different kinds? Bang - bad shift - engine noise - no power... then normal??

Thanks for the help, of course I will post findings and log tomorrow.

[Boost]

I have e-mail notifications on and I saw that someone posted "yes that's limp" but then erased it. I think it is too.

[Boost]

Well, I first scanned the ECM. I found a P1093, which is "Fuel Rail Pressure Low During Power Enrichment". That could explain the weird hesitation he complained about, but there is more. On my LBZ, with my 500 hp program and stock fuel system, just every once in a blue moon during full throttle in the higher gears, it would run into a wall for a second and fall on it's face. It happened about once a month. I called it "defuel" and assumed that the requested fuel was not available so it shut down to prevent a lean condition, although I never logged mine. Could this be the case with this LLY?

On to the test drive. There seemed to be no codes in the Allison controller, when I connected to it and pulled codes, it gave the same P1093. I am guessing any tranny codes would be "P" and stored in the ECM also. Anyways I selected and validated all supported PIDs and went for a short spin. Under some heavier throttle, the trans flared noticeably into the higher gear. It felt like a big momenary slip. He also described that under full throttle when it banged bad, it slipped and then felt like it completely ran out of fuel. I am thinking slipping into the 3200 rpm fuel cutoff maybe? PLEASE LOOK AT THE LOG, thanks! ( I've detuned it since )

[etmotorsports]

Does the truck have a stock torque converter. I have seen truck drive right though it with just a few mods and a healthy tune. I really couldn't tell much from the log i will look at it again.

[Boost]

Thanks! Yes, stock torque converter. Also has intake and exhaust, but the tune is what added the big power. It is not doing it so far with a less powerful tune. Could it slip into the limiter and go into limp? He says it wouldn't drive normal after that until he cycled the ignition. I also suspect the TAPS never experience full throttle learning since I cautioned him so much about the stock tranny and the extra 100 hp.

[vortecfcar]

1093 will put the truck into a fuel limp. You may want to explore fuel pressure relief valve modifications, a lift pump, or replacing the fuel filter. Not necessarily in that order. :)

It's not a trans issue if you don't have any P7xxx codes.

Nick

[Boost]

Thank you! Very good info. And what about the flared shifts? Did the TAPS just not learn yet because he never gets on it fully?

[vortecfcar]

I come from the 'fix one problem at a time' school of troubleshooting. The flared shifts may be related to the fuel pressure issue, or something different. Diagnose that after the fuel pressure is consistent.

Nick

[Boost]

Agreed, thank you Nick.