1998 c70 backfire through inlet

deadmike07 · Post by **deadmike07** » 29 Jul 2014, 09:05

I've got a 1998 c70. I replaced the etm that was running low power and limited revs (limp mode?) With a reconditioned one. Since the swap it has got the power back and will rev as normal, but had developed a miss fire back through the inlet manifold. It gives me a p1238 code which I've worked out as a turbo charger control unit, but i connected a live and neutral and it clicked like I've been told. If any one has any ideas please help me.

Post by **northernlights** » 29 Jul 2014, 20:06

On a naturally aspirated engine, backfires through the intake is usually messed up ignition/timing or a burnt intake valve. I don't know if a turbo engine would be any different. I've seen engines with bad intake valves that won't backfire until you put load on it, so a bad ETM may have masked it.

It's probably worth checking ignition components first, and then a compression test (or even better, a leakdown) if you don't find anything funny with the ignition.

I didn't think the 98's had ETMs? Do you have a distributor or are those coil packs?

Post by **abscate** » 30 Jul 2014, 05:21

1999 model year was first for ELectronic throttle body Or module (ETB or ETM) in a North America, so that mystery is worth noting

The turbo control valve is a high duty cycle solenoid, not just an open/shut. If it's original, it's tired.

deadmike07 · Post by **deadmike07** » 30 Jul 2014, 06:02

Thanks for the info guys. It has individual coil packs and has had new plugs yesterday. Will check the compression as soon as I can. I was thinking that the timing might have slipped a tooth on the belt leaving a valve open when it shouldn't be. And it's an s reg which is late 98 to early 99. I don't have the docs at hand to check the exact date. I did check the valve with a live and neutral and it was clicking like I've been told it does. But might get a new one just in case with new piping

Post by **abscate** » 30 Jul 2014, 09:31

It must be an early "1999 NA model year" or first with Electronic Throttle Body. Coil packs clinches it.

deadmike07 · Post by **deadmike07** » 30 Jul 2014, 09:45

It's not n.a it's the 2.0 turbo model. And the turbo is actually boosting while it's backfiring if that's any help to diagnose the problem

Post by **abscate** » 30 Jul 2014, 13:43

Aha - I am a victim of my own acronym

Here NA meant North America, not Normal (natural) Aspirated, nor numerical aperture, nor National Association