2g limp mode

Jon Lane · Apr 26, 2015

Trying to diagnose a persistent limp mode in a late 2g Tsi 5spd. Car goes into limp when warm, and resets back to normal after it cools and then runs fine for five miles or so, including in boost.

Coils check okay. Plugs are new, wires are also fine. Reset ICM connector a few times, and checked big connector on the MAF. Manual trans and so no trans related limps. Has only CEL'd a 0300 general misfire. Rebuilt throttle body w/ new gaskets, new water pump and timing, new thermostat and stable temps, car runs very well when not limping. The only other recent change from habit was a swig of Lucas fuel system cleaner.

I'm asking myself how likely the culprit could be an injector, ICM/power transistor, or the dreaded ECU, which is stock and unmodded. I'd appreciate some input...

Type1DSMr · Apr 26, 2015

Check the gap of your plugs should be at .28 and also which plugs do you have. Also do a boost leak test. Do you have a wideband sensor by chance?

Jon Lane · Apr 26, 2015

Appreciate the reply. O2S are original and upper O2S is new - forgot that. Plugs are fairly new NGK BPR6ES but I'll gap em again. Haven't done a boost leakdown.

Type1DSMr · Apr 26, 2015

Yes definitely check the gap. I had a set somehow loosen up to .34 when I gapped them at .28 according to my gapper from autozone and I threw multiple misfire code and went lean until I shut my car off and restarted. Re gapped them and was good to go.

Jon Lane · Apr 26, 2015

You'll love this: Checked the BPR6ES I'd gauged with an AutoZone gapper to find they'd all opened up to group between .31 and .36. I kid you not.

Car idles like a top for the time being, but I'll have to see if it wants to keep running when actually driven somewhere. Really appreciate your insight...

Type1DSMr · Apr 26, 2015

Haha nice, I take it you re gapped them at .28. Glad I'm not the only one now with that problem with an auto zone gapper.

Jon Lane · Apr 28, 2015

Well, it's not plugs. Went into limp mode again today.

With a plug wire disconnected, are the coils able to arc from the tower over to the laminations stack and the coil bracket or is that a bad tower? Pulling a wire results in a lot of sparking from the coil tower across the lams to the engine ground at the bracket mounting on the intake manifold.

bmxfelon420 · Apr 28, 2015

Hmm general misfire? Not Random misfire? Random misfire is usually a CAS issue if it's not an actual misfire. Does it go away if you shut the car off/turn it back on?

Jon Lane · Apr 29, 2015

The car will not reset itself that I recall and I'm trying to short the hot leads to ground for awhile to reset it. Both cam and crank sensors are recent replacements and should be fine.

Just replaced the coil that arced when the wires were pulled and if the car resets I'll test that, plus report any CEL that appear. Had some P0300 randoms recently, but I don't know if they're related.

rtrocket59 · Apr 29, 2015

Is it only going into limp mode when you enter closed loop? Or just when the car is warm?

Jon Lane · Apr 29, 2015

100% of the time it's completely warm, and all but once it was at idle.

(Trigger plate is new too, and it's not wet. New front end seals at all four locations and the front of the motor is nearly dry.)

Jon Lane · Apr 29, 2015

I may have to take that back about oil in the front cover. It's leaking a little again. How sensitive are the crank angle sensors to being wet?

rtrocket59 · Apr 29, 2015

Did this start to happen after replacing a certain part?

Jon Lane · Apr 29, 2015

It happened about a month after a new head gasket, oil seals, timing set, water pump, cam sensor, and a general freshening up. No electrical, ignition, or fuel changes, except for a dose of Lucas fuel system cleaner.

Car has since seen maybe 500 miles and a week ago started going closed loop again and again, usually within 20 minutes of starting.

rtrocket59 · Apr 29, 2015

It sounds like a short to ground but it also sounds like an overcharging issue.... Can you check your battery voltage with engine off? At idle? And at 2500 RPM? Do you have a digital multi meter?

Jon Lane · Apr 30, 2015

Off voltage is 12.25v. 2krpm is 14.35, and 1krpm is 14.23, both of which are over 13.8v but less than 5% over.

What are the odds this is the ICM / power transistor?

Also, car will reset itself, I've found. It just takes overnight.

Jon Lane · May 2, 2015

I should add that the FIAV is disconnected so there's a little idle surge. Could that trigger closed loop?

Jon Lane · May 2, 2015

ICM / igniter / transistor tests okay.

In limp mode there's an odd, intermittent clicking or snapping centered right on or in the ICM. No visible arcing. At first I thought it was an injector, but it's further back. It's done this from time to time for a long while. It seems to appear any time the engine idles poorly.

Each coil tested by swapped it for a new one. Currently there's one new and one old in the pack.

bo0st · May 2, 2015

If you had link it'd be easy to diagnose this but it's a PITA with a stock ECU.

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