Tuning - misfires at high(ish) boost - Page 2 - Pontiac Solstice Forum
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post #16 of 38 (permalink) Old 01-02-2019, 10:17 AM Thread Starter
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Thanks for posting that service bulletin. It’s not clear to me if that stuff can be sprayed through the throttle (with the plate open) or if the intake manifold needs to come off. ??

Why would the carbon buildup issue only present at higher boost? I can create the misfire at 3500-4000 RPM (under load) if the boost is high.

When the weather was a little warmer, the GMPP tune was making closer to 18PSI, and the 15# number is in 2nd gear. I haven’t tested on the highway yet, so getting up to higher RPMs, under load, out of 1st gear hasn't happened.

I *can* get 18psi-20psi in neutral (sitting in the driveway) if I floor it, at which point it misfires even on GMPP.

Putting the car back to stock won’t really help here since the problem only happens at boost levels higher than those allowed by the stock tune.

I may try copying the air load tables and wastegate duty cycle table over from the other tune to GMPP just to up the boost and see what I get. Which hopefully won’t include detonation and holes in pistons.

Blue-ish 2006 2.4, Werks stage 1 turbo, Borla cat-back, DDM braces, Spec aluminum flywheel, Spec stage 2 clutch, Werks aluminum radiator, some gauges, RKSport hood, Morimoto FX-Rs, GReddy Profec, Norm's fenders

'07 GXP, RPM Stage 2, Solocatless downpipe, TCE Wilwood 6 piston front brakes, 4-piston rears , Stainless brake lines, slotted/drilled rotors, BC Racing BR coilovers, Performance Autowerks intercooler, DDMWorks CAI, charge pipes and braces

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post #17 of 38 (permalink) Old 01-02-2019, 12:07 PM
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OK, i'm puzzled... how do you get carbon buildup on a direct injected engine; and how does a gas treatment help prevent that???
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post #18 of 38 (permalink) Old 01-02-2019, 12:35 PM Thread Starter
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My limited research indicates that the buildup comes from the recirculated exhaust gases and, over time, builds up on the valves. The "Top Engine Cleaner" helps to break that gunk up. I assume that, at that point, it gets sucked into the cylinder and hopefully makes its way out the back without clogging up the turbo or the cat. :/

Blue-ish 2006 2.4, Werks stage 1 turbo, Borla cat-back, DDM braces, Spec aluminum flywheel, Spec stage 2 clutch, Werks aluminum radiator, some gauges, RKSport hood, Morimoto FX-Rs, GReddy Profec, Norm's fenders

'07 GXP, RPM Stage 2, Solocatless downpipe, TCE Wilwood 6 piston front brakes, 4-piston rears , Stainless brake lines, slotted/drilled rotors, BC Racing BR coilovers, Performance Autowerks intercooler, DDMWorks CAI, charge pipes and braces
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post #19 of 38 (permalink) Old 01-02-2019, 12:42 PM Thread Starter
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Quote:
...induce the cleaner through the throttle body or an engine vacuum hose/pipe.
Okay, through the throttle it shall go. I went ahead and ordered the Delco cleaner from Amazon. If it works, it's a cheap fix.

Blue-ish 2006 2.4, Werks stage 1 turbo, Borla cat-back, DDM braces, Spec aluminum flywheel, Spec stage 2 clutch, Werks aluminum radiator, some gauges, RKSport hood, Morimoto FX-Rs, GReddy Profec, Norm's fenders

'07 GXP, RPM Stage 2, Solocatless downpipe, TCE Wilwood 6 piston front brakes, 4-piston rears , Stainless brake lines, slotted/drilled rotors, BC Racing BR coilovers, Performance Autowerks intercooler, DDMWorks CAI, charge pipes and braces
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post #20 of 38 (permalink) Old 01-02-2019, 02:52 PM
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The threads referenced describe the phenomenon in some detail. Basically in a normally injected engine, the incoming fuel washes off the intake tract and the valve. In the DI engine there is no fuel to wash the surfaces clean.

When the engine is running and hot, any hydro carbons coming into the intake, either via the PCV overflow or from the turbo "washes" the intake and is apparently not a problem when running. It flows in the heat and gets burned as designed. But once you shut the motor down, if there is any oil or unburned hydro carbons in the intake it can "plate out" on the intake valve and the intake tract surface as they cool. Each of these cooling cycles can result in a very small buildup of carbon and over time it gets significant. If you kept the valves hot all the time, no problem but they will eventually cool off and form deposits that remain through the next run cycle.

The "best" way to remove them is to mechanically remove them. Either by using a brush or by media blasting them and then sucking the loose carbon out with a vacuum.

Apparently the way that GM does it is to remove it chemically. They say warm the car up, blast the intake with the right amount of chemical, wait THREE hours and run the car. The chemical is supposed to transform the hard carbon deposits into soft or even semi liquid deposits that then pass through the combustion chamber and out the exhaust.

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post #21 of 38 (permalink) Old 01-02-2019, 02:58 PM Thread Starter
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Cool - thanks for the detailed explanation.

On the LE5, removing the intake manifold is a 15 minute process. Not sure about the LNF. If the rain ever stops, I'll go ahead and yank it off. I found a video from one of the Cobalt SS guys showing the cleaning process, and it looks pretty straightforward.

In the mean time, I ordered a cheap bore scope (really "needed" one, anyway). I'll check the accessible valves through the vacuum port on the manifold. With 100k miles, I'm sure it's going to look pretty terrible.

The real question is if this will impact the misfire issue. The TSB implies that it will, and it's worth taking care of in any case. Fingers crossed.

Blue-ish 2006 2.4, Werks stage 1 turbo, Borla cat-back, DDM braces, Spec aluminum flywheel, Spec stage 2 clutch, Werks aluminum radiator, some gauges, RKSport hood, Morimoto FX-Rs, GReddy Profec, Norm's fenders

'07 GXP, RPM Stage 2, Solocatless downpipe, TCE Wilwood 6 piston front brakes, 4-piston rears , Stainless brake lines, slotted/drilled rotors, BC Racing BR coilovers, Performance Autowerks intercooler, DDMWorks CAI, charge pipes and braces
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post #22 of 38 (permalink) Old 01-02-2019, 04:09 PM
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Part of the challenge is the buildup is "random" so each cylinder can develop its own pattern of buildup.

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post #23 of 38 (permalink) Old 01-02-2019, 05:47 PM
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Quote:
Originally Posted by raygun View Post
Thanks for posting that service bulletin. It’s not clear to me if that stuff can be sprayed through the throttle (with the plate open) or if the intake manifold needs to come off. ??

Why would the carbon buildup issue only present at higher boost? I can create the misfire at 3500-4000 RPM (under load) if the boost is high.

When the weather was a little warmer, the GMPP tune was making closer to 18PSI, and the 15# number is in 2nd gear. I haven’t tested on the highway yet, so getting up to higher RPMs, under load, out of 1st gear hasn't happened.

I *can* get 18psi-20psi in neutral (sitting in the driveway) if I floor it, at which point it misfires even on GMPP.

Putting the car back to stock won’t really help here since the problem only happens at boost levels higher than those allowed by the stock tune.

I may try copying the air load tables and wastegate duty cycle table over from the other tune to GMPP just to up the boost and see what I get. Which hopefully won’t include detonation and holes in pistons.
Thats interesting
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post #24 of 38 (permalink) Old 01-02-2019, 07:01 PM
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the 'carbon plating' of the intake runners is insignificant compared to the buildup on the valves and is of little consequence unless it liquifies or shrouds the valves.

the CRC product is less than 1/2 the price of the GM, and there seems to be other similar products
Bill

Last edited by wmf246; 01-02-2019 at 07:11 PM.
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post #25 of 38 (permalink) Old 01-02-2019, 07:12 PM
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If you had significant carbon build up it would likely not only effect the intake tract but also the value seats. If it effected the value seats you would see that in the compression test you did. If you are getting that bad of a misfire under load at high boost my guess would be fuel starvation or too much timing leading to knock. Where did you get your tune?
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post #26 of 38 (permalink) Old 01-03-2019, 04:11 AM
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In my reading it does not affect the seats. If you do a search there are several threads with pictures. It appears on other DI cars as well

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post #27 of 38 (permalink) Old 01-03-2019, 09:29 AM
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For what it's worth, I've had significant carbon buildup on my intake valves twice due to oil getting into the intake. Once from a bad PCV valve and once from a turbo that was on its way out. I never had much luck with solvents, I ended up walnut shell blasting the valves.

Misfire at boost was never an issue for me even when they were badly gunked up. The only symptom I had was a random cold start misfire CEL. The CEL would set between 10 and 40 seconds after starting the car. The best way to check for buildup is to pull the intake manifold. It's a pretty easy job and the one way you'll know for sure if that's your issue.
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post #28 of 38 (permalink) Old 01-03-2019, 10:16 AM
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I'm surprised noone has asked this yet, but....If your Gmpp tune is only giving you 14psi.... What amount of boost were you seeing stock? Also, it could be possible at the 15psi boost level that you are blowing out spark slightly. What do you have your spark plugs gapped at?
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post #29 of 38 (permalink) Old 01-03-2019, 01:40 PM Thread Starter
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I'll flash it back to stock this weekend and compare boost levels vs GMPP. What sort of boost should I expect from the GMPP tune? I also need to get it out on the highway and log some WOT pulls.

Spark plugs are the Delco 41-108s, which come pre-gapped.

Also, I previously had a CEL due to multiple random misfires, even before the new tune. There's something else going on here. I replaced the HPFP recently, but as far as I can tell the new one is working fine.

It's still a balmy 40° F here; supposed to be back up close to 70° in the next day or two. New Year's resolution: clean out the garage so that my wrenching time isn't restricted to good weather days.

Blue-ish 2006 2.4, Werks stage 1 turbo, Borla cat-back, DDM braces, Spec aluminum flywheel, Spec stage 2 clutch, Werks aluminum radiator, some gauges, RKSport hood, Morimoto FX-Rs, GReddy Profec, Norm's fenders

'07 GXP, RPM Stage 2, Solocatless downpipe, TCE Wilwood 6 piston front brakes, 4-piston rears , Stainless brake lines, slotted/drilled rotors, BC Racing BR coilovers, Performance Autowerks intercooler, DDMWorks CAI, charge pipes and braces
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post #30 of 38 (permalink) Old 01-03-2019, 01:42 PM Thread Starter
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Quote:
Originally Posted by wmf246 View Post
the CRC product is less than 1/2 the price of the GM, and there seems to be other similar products
Bill
What is "CRC?" I'm thinking error detection & correction, but that can't be right.

Blue-ish 2006 2.4, Werks stage 1 turbo, Borla cat-back, DDM braces, Spec aluminum flywheel, Spec stage 2 clutch, Werks aluminum radiator, some gauges, RKSport hood, Morimoto FX-Rs, GReddy Profec, Norm's fenders

'07 GXP, RPM Stage 2, Solocatless downpipe, TCE Wilwood 6 piston front brakes, 4-piston rears , Stainless brake lines, slotted/drilled rotors, BC Racing BR coilovers, Performance Autowerks intercooler, DDMWorks CAI, charge pipes and braces
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