My car is a 05 Sunfire m62, 3.0 pulley, dual pass, meth, running the reflash. So I'm assuming what I'm experiencing is detonation. When I hit boost, the car hesitates, pulls timing (I've seen down to -5 on the scan gauge). Started happening since I swapped injectors to the GMPP kit from the LSJ Green tops (leaking). I turned the meth to come on sooner remembering reading somewhere that the kit injectors were a touch smaller than the green tops. This seemed to work for the test drive I took it on and the ride into work the next morning. On the way home, the hesitation and pulled timing is back. It seems to happen when its hotter outside. I'm seeing IATs up to 130* sitting and I can't seem to get it under 101* with the meth spraying and dual pass and it seems to hover 120* when cruising. I didn't look at a thermometer and I'm no meteorologist, but saying it was 80* was probably pushing it today and I don't remember seeing 130's at all last year. To me, this seems to be the area I need to investigate. Does anyone else have any suggestions?

What are the iat's during a WOT pull?

You could be having spark blow out. what is your plug gap?



FU Tuning

as a general referance, GM says that (with the cobalt heat exchanger system) that IAT's 25 degrees above ambient air temp are perfectly normal on these blower setups.. I agree that it sounds like spark blow out.

I get 7-8 deg pulled.....i dont even bother getting into boost....so maybe I have the same issue?

Im on the stock pulley, but no cooling mods. But even when my IAT's are 70deg it knocks like crazy.

Im getting the same symptoms. First and second it doesnt really knock to bad but anything above that it does. Im running the one stage colder plugs with the stock gap.....I think its .040


Sorry to thread jack but it sounds similar to my issues, which I know arent helped by no exhaust and no cooling and a crap tune.

109-ish on a good pull seeing around 10 psi.

If I remember correctly, .032. Just replaced them I'd say less than 15k ago. They didn't have NGKs @ Autobone so I got the Autolite equivalent. I ordered the 2 heat range colder NGKs this week as a spare set. Maybe I'll just throw them in when they get here. Wouldn't I notice a change in AFR with blow out?

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Im running the one stage colder plugs with the stock gap.....I think its .040

Thats too much gap. Try 0.32

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Just replaced them I'd say less than 15k ago. They didn't have NGKs @ Autobone so I got the Autolite equivalent. I ordered the 2 heat range colder NGKs this week as a spare set.

15k is a good amount of miles on a boost set of plugs. At the very least check the gap, they could need regapped.

I personally hate autolites and have had eco's eat them up.



FU Tuning

Would the car actually pull timing if it's spark blow out? The AFRs would go rich with blow out, if that's actually what's happening. Does this happen both with and without the water/meth spraying? Too much water will cause a misfire that feels like what you are describing. What is the mix and the nozzle size?

By all means check your plugs (recommend appropriate NGKs or ac delcos), but i've never seen spark blow out on an M62 eco.

It starts to happen as the boost gauge starts to get out of vacuum. Basically any kind of load on the engine what so ever. I don't think my meth turns on till about 4-5psi right now. Im on a 50/50 mix and it's probably a small nozzle as i told the guy at coolingmist.com I was only making 200 hp. Im kind of tempted to pull my cat off and see if its partially clogged.

Richard Edmondson wrote:It starts to happen as the boost gauge starts to get out of vacuum. Basically any kind of load on the engine what so ever. I don't think my meth turns on till about 4-5psi right now. Im on a 50/50 mix and it's probably a small nozzle as i told the guy at coolingmist.com I was only making 200 hp. Im kind of tempted to pull my cat off and see if its partially clogged.

Do you have a wideband on your car?

If so what is it doing at the point of this happening?



FU Tuning

I have an AEM UEGO. Its reading anywhere from 14.5 to 10.4. The 10.4 being in boost.

Richard Edmondson wrote:I have an AEM UEGO. Its reading anywhere from 14.5 to 10.4. The 10.4 being in boost.

When you feel this hesitation what is the wideband reading? You said the hesitation happens right when the boost/vac gaiges goes from vacuum to boost, so 1-2psi. What is the reading that that point?

Also is it only at WOT?



FU Tuning

Its at the 14.5 reading and its at any kind of throttle.

14.5 is lean for boost, BUT at light throttle it is not as big of a concern and is what the ECU is setup to do.

Next question is it happening at a certain RPM?

I truly think you just need a custom tune.



FU Tuning

That AFR reading is just as its coming into boost.

RPM doesn't seem to be a factor as I'll be going up a hill, timing gets pulled, car bogs, I downshift, same result.

Swapped plugs yesterday and had no effect. Old plugs had black soot on threaded base facing into the chamber and the electrodes were a white ash-like color. Lean maybe?

I know a custom tune is the solution, but even with extensive reading, tuning just escapes me.

To me it sounds like car is still in closed loop this is why the AFR's are as lean as they are.

With a good tune this should be able to be resolved.



FU Tuning

Yeah I have notice for a little while before this whole mess started that the car would stay in closed loop while in boost for some time. AFR's would stay around the 14.4 to 15.4 range then it would be like someone hit a switch, car would go faster and AFRs would be in the 11's. I did notice that it was staying in closed loop on the Scangauge and the second the car would go faster, it would be in open loop.

Ah, well it makes sense now. You can usually get away with the first few psi in closed loop (~14.7:1), but too much or too long in boost at that afr, especially from a roots blower, and your asking for knock. The extra fuel cools the charge and cylinder temps. On a 3.0 pulley, you should be going PE at no greater than 40% TPS in my opinion. No leaner than 12.0:1 in PE if you really want to push it, 11.5:1 is more towards the safe side. Keep in mind that methanol will contribute to fueling, and if it cuts out for any reason, it will go leaner.

Fixed it. Finally threw p0327 today for the knock sensor. Pulled it off and the wire was broken. Swapped it out with one I had lying around and no more pulled timing. Thanks for all the help guys.