back fire through intake when in gear

[aureliusmaxed]

Hi guys. We have a 1998 Boxster in the shop. It's a JDM with 53,000 KM. Tiptronic.

 

The symptoms are a backfire through the intake manifold when in gear, hesitation and lack of power won't go through the RPM range.

 

What we have done; freshen the gas with new

replaced spark plugs

replaced maf

replaced engine coolant temp sensor

unbolted catalytic converter and ran without it to test for a plugged system, without change

 

the symptoms occur only when in drive. when in park and neutral, we can rev the engine and the soft rpm limiter stays at 4K rpm. 

however when the car is lifted onto the hoist we put it in drive, and then we get hesitation and backfiring through the intake, when we press onto the accelerator.

 

i have connected to the durametric and cleared/short tested for all systems and the software returns no fault codes. we also did live stream of the maf, throttle position, ect, and rpm, throttle position angle and didn't find any irrational values.

 

we're about to run a fuel system pressure and volume test.

 

update: i finished talking with the tech and he says that with the MAF UNPLUGGED, the problem went away and it worked all the way to red line. we didn't actually replace it with a new one yet.

Edited November 3, 2016 by aureliusmaxed

[txhokie4life]

Check for air leak post MAF -- 

 

Had something similar and found that the jboot had worked its way loose.

 

Mike

 

[Loren]

Any fault codes or pending faults?

[aureliusmaxed]

1 minute ago, Loren said:

Any fault codes or pending faults?

none Lauren. there were some initially that were caused when the technicians were removing sensors but after clearing/running short test again there is no faults. 

[Loren]

I agree that since this happens under load an air leak is likely. But you usually get a fault when that happens.

If you have a smoke machine it is likely a time to use it.

[aureliusmaxed]

19 minutes ago, Loren said:

I agree that since this happens under load a air leak is likely. But you usually get a fault when that happens.

If you have a smoke machine it is likely a time to use it.

 

sorry there was some miscommunication with the techs. i am about to determine if running without the MAF plugged in. we have ordered a new MAF AND will update this thread later.

Edited November 3, 2016 by aureliusmaxed

[aureliusmaxed]

turns out the spark plug boot wires were bent in such a way that they were shorting to the engine and not getting to the plugs. the issue is now resolved.

[Loren]