Sudden bog under boost, engine falls flat on its face.

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forcefed86

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Jul 28, 2005
(combo in sig)

So after winter storage I had some issues with an injector not firing. Sent out the ECU to have driver replaced and the car starts up and idles and drives perfect. All scan master items in check. MAF readings are normal. Only CEL error is a code 23. Which I always have. I'm using a turbo tweak chip and don't need the intake temp sensor.

When I go WOT, boost will build fast to 24 psi or so and then the car acts just like a coupler blew off. It starts to loose power quickly and bleeds off boost, then it abruptly falls flat on its face coughing and sputtering. At this time the AFR gauge pegs dead rich. I'm getting no knock readings.timing is at 18* AFR's 11.6:1. Compression test is good all around. I pressurized the inlet of the turbo and checked for leaks on the entire car. There is a slight crack in the intake manifold I've had since last season. I need to fix this, but the car ran fine with this small crack all last season. I leak checked the system to 40psi and had no other major leaks.No couplings blew off etc. I don't run a BOV. I just don't know where I could be losing pressure at?

I replaced the MAF with a spare unit I had with no change. Turbo is new and tight. No smoke etc.

Car runs great other wise. I'm stumped... again!
 
If its going rich.. That means the fuel isn't being burned right? Bad spark? What have you for plugs? New? Plug wires? Check your coil pack?
 
ZNix said:
If its going rich.. That means the fuel isn't being burned right? Bad spark? What have you for plugs? New? Plug wires? Check your coil pack?
Click to expand...

Wires are 8mm magnacores deals. Plugs are last seasons (prob 20 passes on them and 500 street miles or so). I'll change them out, but I doubt thats it. Thanks for the suggestion. I'll eliminate that possibility at least.
Coil pack and module are newish. Bought them last year. High output coil pack and a magnovox OEM replacement IGN module. Went through a few modules until I found this one. Seems I always have problems with them in the past. But this is a new problem. It's not like ignition break up. More like the boost is leaking somewhere. (which I'm pretty sure is impossible).
 
Does boost stay steady on the gauge? If it does.. I don't think the boost would be leaking anywhere. Hmmm..
 
What happens at say 3/4 throttle? TPS setting correct? You are either getting too much fuel, not enough spark or not enough air to be running rich. How old is the O2 sensor?

Bryan
 
turn the boost down and see if it clears up.

I had a bad coilpack act that way. The engine felt like it was dropping a couple cylinders (which I'm sure it was), boost would peak and then fall off to 15 psi or so.

Bob
 
11.6 is on the lean side. With E85, you can run 10.8:1 and the car will be just as fast (or darn close, but you will be safer)
 
ZNix said:
Does boost stay steady on the gauge? If it does.. I don't think the boost would be leaking anywhere. Hmmm..
Click to expand...

Yes the boost drops on the gauge. As soon as the boost peaks as I said it acts like a coupler let go boost drops as well.

Phoneguy said:
What happens at say 3/4 throttle? TPS setting correct? You are either getting too much fuel, not enough spark or not enough air to be running rich. How old is the O2 sensor?

Bryan
Click to expand...

The engine just bogs very rich at 3/4. TPS is .44. WB02 as about a year old. E85 doesn't carbon them up like pump gas though. The sensor calibrates to free air as it should. Seems to be right on at idle and cruise.

TurboBob said:
turn the boost down and see if it clears up.

I had a bad coilpack act that way. The engine felt like it was dropping a couple cylinders (which I'm sure it was), boost would peak and then fall off to 15 psi or so.

Bob
Click to expand...

I usually run between 10.3 and 10.8 on the AFR. But anything richer and the car would just bog on the initial spool-up. It doesn't stay in boost long that way.

With boost down the car is dead rich. I was told by eric this is the nature of the chip. It was burnt for 35lbs of boost. I usually run 30ish. After the MAF count peaks the fuel table is very rich.Previously I'd have to drop out alot of fuel to run 12psi (wg pressure). If I turned up the boost it would then be lean. But it never pegged out the WB02 rich like it does now at low boost.

I did try adjusting it down to -20 on the WOT fuel. This will flash around a 12.5 AFR around 1-2psi then it jumps to 11.6 or so and does as stated above. I've had IGN issues in the past with this car and it feels nothing like that. The boost actually falls off rapidly as soon as it peaks. You feel the car accel hard as it should for a brief second. Then you feel it slowing slightly like its pulling a ton of timing then the boost drops rapidly and it loads up with fuel. KR seems to be working as I get the audible tone when cranking at times. Also I'd get the standard 2-3 counts on the shift. I did try 15* of timing and 21* of timing with no changes.

Compression test was good, I think i'll try a leak down test today and see if I turn up anything. I just think it odd that the car runs so well out of boost. Makes it hard to believe it's something major like rings, hung or damaged valve etc... No oil in down pipe or oil smoke etc...

Thanks all this ones got me puzzled! I'll try to get some video if I don't figure it out soon, don't think it's a "normal" TB issue.
 
Had some Autolite spark plugs go bad before and would act just as you describe. That would be too easy though. :p

RL
 
Didn't have much time sunday, but new plugs didn't help. I'll replace the wires soon to just to rule it out. I suppose I'll pull the intake and patch or replace it. Although I did pressurize the entire system with shop air to 40psi. The crack was leaking pressure for sure, although not enough to go from 25lbs to 10 in a brief second. The 72mm charger should be more than able to compensate for that small leak. Hopefull I'll find something I missed when I pull the intake.

thanks all!
 
TurboBob said:
turn the boost down and see if it clears up.

I had a bad coilpack act that way. The engine felt like it was dropping a couple cylinders (which I'm sure it was), boost would peak and then fall off to 15 psi or so.

Bob
Click to expand...

I've had similar experiences like that a couple times over the past 10-15 years. Always ended up being a bad coil pack.
 
Well I replaced the coil pack with my old known good unit and it made no difference. Doesn't make sense if I drop the boost as low as I can go (around12lbs) it goes dead rich and sputters. If I crank the boost up it will blip rich for half a second, then lean to a decent afr and pull very quickly to 20psi and it acts just like a coupler pops off. No ignition miss sounds etc. Yet a shop air pressure test holds tight to 40psi with only a slight leak on the intake. Suppose the module could be shot. I seem to replace those all the time, yet they never end up being the problem.
 
if fuel isnt being burnt it will read lean, the wideband reads oxygen content not fuel content
 
What kind of intake ducting to the turbo do you have? If it's some sort of flexible hose, it could be collapsing with high boost.
 
kidglok said:
if fuel isnt being burnt it will read lean, the wideband reads oxygen content not fuel content
Click to expand...
Makes sense to me, although if it isn't fuel... and it isn't spark...what is it?

The car drives great out of boost, so it has to be pressure related. The turbo is a new unit. The compressor side seems in good health. Maybe I'll pull the exhaust side and make sure it isn't heating up and seizing or something really odd. (thats what it feels like it's doing anyay) I really don't know how else to approach this issue.

I did just have the ECU out to bob for a driver repair. May try another ecu I suppose. He said it functioned great on the bench so I doubt thats an issue. Never heard of a chip going bad.

I run a maf translator, not using the timing control on it. The maf translator seems to be working according the the SM2. Idle/cruise maf countss are normal, it seems to max out the MAF settings once in boost as it alwasy has. I swapped out a known good MAF just for kicks. No change.

I suppose the fuel pressure could be dropping under load. I have verified it raises with boost on the trans brake. I don't have a gauge in the car however. And I'd guess this would show up as sudden lean readings on teh wb02 which it does not.

Sorry, I'm just rambling...but this MAKES NO SENSE! :mad:
 
tonka said:
What kind of intake ducting to the turbo do you have? If it's some sort of flexible hose, it could be collapsing with high boost.
Click to expand...

I run 3" alum piping, but my filter is boxed in the driverside lower fender area. I'll check the filter and make sure nothing strange is going on. Thanks for the idea! Would be funny if I left a rag stuffed in the piping or something.
 
kidglok said:
if fuel isnt being burnt it will read lean, the wideband reads oxygen content not fuel content
Click to expand...

This is backwards. His chip is delivering fuel for 24psi+ and it falling on it's face, so it'll read rich if the fuel isn't getting burnt.
 
how are your wires? have you pulled plugs? a piece of plug couldve broken loose and damage your exh wheel...but turbo wouldnt work after that or would it? so you've gone WOT with no boost? and everything runs ok?
 
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