Bad hesitation/cutout and backfires

[Turbo6inKY]

Okay, just limped my car back home from Atlanta (see the southeast forum for mild details).

Basically, the story is this: Car ran fine on the way down, got to tech inspection at the event I was entered, guy shook the MAF real bad, car starts hesitating and popping and sputtering whenever you give it a good throttle input.

Changed fuel filter. No change.

Got in touch with Dana Wyatt, he didn't think it was the MAF. We checked the coilpack (what its doing feels like its hitting a spark-cut rev limiter... at 3000 rpm). Bad center coil (and the fouled plugs to prove it.

Okay replaced the coil, two fouled plugs. Runs much stronger until it cuts out again.

Switched out ignition control module. Same problem

Disconnected cam timing sensor. Same problem

Disconnected MAF. Same problem

Changed out all the plugs and the plug wires. Same problem.

Suspected plugged CAT, cut it off. Same problem.

Gave up and limped it home.

So, I just hooked TurboLink up to it. My TPS is set fine and registering throughout the range. The MAF is giving me a signal at idle and on-throttle (not moving). O2 is working (cross counts are good). I suspected possibly fuel pump, but I've hotwired it on and run it for ten minutes without hearing a stumble or seeing a variation in pressure on my gauge (rail mounted, can't watch it while car is moving). The system is holding pressure after turning the car off, so I'm not suspecting a leaky injector yet.

On the road, it will maintain a constant throttle setting, but ast soon as you tip in, it cuts out.

Gas mileage was around 17mpg on the way home. I'm running stock injectors and chip, fuel pressure is set at 40psi.

I'm getting a new inlet tube welded onto the cat so I can put it back on and not annoy my neighbors when I take it out for a load test, so no tests with it actually moving until probably tomorrow.

It is running rich. Very rich. Off-idle O2 millivolts are in the mid 800s, and on the way back from Atlanta, the thing let out some incredible backfires. Popped it right next to some lady in an SUV on I-24 in Tennessee and she almost swerved off the road.

I'm still suspecting the MAF. I've found a couple posts describing similar behavior, and the fact the problem started right after that dude shook it kinda keyed me in. I'm waiting on a translator and a 3" Declo LT1 MAF right now.

In the meantime, what I can I check? Cam sensor alignment? Crank angle sensor? EGR?

Thanks in advance!

 

[Turbo6inKY]

No help? Nobody has run into this?

 

[GotGas8668]

sounds semi familiar

have you tried the "tap test" on the MAF? take the handle to a screwdriver and with the car running tap it firmly and see if it changes any when you do that if it does i would look into getting a new MAF

other than that my car suddenly started running horrible (but all the time) i found a missfire on one cylinder checked compression good checked leak down good checked coil and ignition not the problem replaced a lot of things and finally tore the motor apart ended up having burnt exhaust valves and the exhaust valve on the cylinder that was missing was burnt a little worse that the rest this was causing the car to show good compresion but not be able to hold it under combustion i made a thread about it a while back and input any informatin i did to the car or anything i found out just do a search under my screenname and you should be able to find it

hope any of this helps

 

[TurboGN]

I'm also leaning toward the MAF. I'd be nice if you had a spare or could get a loaner. Good luck, Joel

 

[Mr.Buick]

Engine backfires

I had the same problems untill I replaced the MAF, what readings are you getting on the turbolink? you need at least 5-7 at idle and should be close to 200-250 WOT depending what air flow you can get through the filter.

 

[Turbo6inKY]

Fixed.

It was the MAF.

 

[RUQWKNF27]

Hum!!!!

If the car was fine up untill the moment the guy shook the Maf, then I would think it was pretty evident that the problem lied with the MAF. Next time I saw hi I don't think i would "shake" his hand, unless you gave him your new receipt for the replacement maf.

 

[Turbo6inKY]

Okay, more driving and watching has revealed that all is still not well.

First, car idles like poo on the stock chip. Dies after the first cold start, then hunts around. My Thrasher idles better, but it still stumbles every now and then.

TPS is set fine and responds well.
Haven't checked the IAC, but with the thrasher fixing the idle, I'm inclined to think the IAC is working fine.

On throttle tip-in, I sometimes get a hesitation accompanied by a pop. The pop is visible on the boost gauge, so something is expanding rapidly into the intake manifold.

I did notice that in 20 miles of driving I recorded on my TurboLink last night, EGR duty cycle never moved off of 0%.

Boost builds a lot slower than it did before all these troubles started.

I have an exhaust leak at the inlet to the catalytic convertor. Possibly one on the driver side header, haven't pinpointed it for sure yet.

All the problems except for the boost building slowly (which is simply a subjective observation, I could be imagining it) go away after the car gets good and hot.

Can anybody think of anything else I should check?

btw: Don't drive to Atlanta, it is bad for your car.

 

[Turbo6inKY]

Well, crap

Finally got a flashlight out with some soapy water and...

Driver side header cracked between 3 and 5. Score.

Probably accounts for the high BLMs I've been getting too.