Backfiring at low RPM

unclebilly · unclebilly's Garage

1986 Euro 930
Garretson I/C, k27, 964 cams, k&n filter with plastic housing.

My car was running OK but I noticed it was smoking under hard acceleration. I had the car flatbedded home.

I determined that the turbo oil line was leaking and oil was burning off on the exhaust.

I replaced the oil line but noticed oil in the intake hoses etc.

I set the intake valves. I set the timing.

The car now has a backfire and won't idle for long.

It could be a vaccum leak, it could be ingnition. I took the car for a drive and could not get more than .6 bar of boost on the 934 gauge. When I go home, oil was coming out of the k&n filter on the turbo oil tank vent hose that is tucked in under the I/C.

Apart from the backfiring, could my turbo be pooched?

For the backfiring, I pulled the cap and rotor and both look ok. I will check the leads - I put the stock sheilded leads back on while it was apart. Any other thoughts?

Jim2 · Jim2's Garage

The low speed backfires and poor idle comes across as a vacuum leak. Since you had the intake off in order to service the turbo oil feed line perhaps you overlooked some connection when you R and R'd the intake/intercooler. Also, you might change back to the other set of plug wires which you mention you changed - nasty crossfire with the new plug wires????? Make only one change at a time in order to decipher the issue - you know the drill.

Only being able to make .6 bar of boost sounds like your intercooler is coming unseated and or an O-ring has escaped, but .6 bar could be a result of your vac leak, though it usually takes a larger aperture than that of a vac line or even the decel valve fittings to bleed off what a turbo compressor wheel can generate.

On your 3rd point, once you have the above sorted, check your oil separator to ensure the oil drain-back hose is not kinked or blocked somehow which would be causing excess oil in your intake system. Since your car is local I'm aware the motor was overhaul recently and I doubt it has excessive blow by but you could compare to your OTHER 930s breather vent hose to judge if there is an issue.

Good toys you got, motor on you lucky dog!