I've just done the intake manifold, plenum and runner gaskets and now I've got slight pinging under gentle acceleration, and a rough idle with occasional stall. At the same time I also did fuel filter, plugs and O2 sensor and removed the restrictions / smoothed out the front of the plenum chamber.

Spark leads are all secure and in the correct firing order. I found one vacuum leak from a split in the PCV hose but haven't found any other vacuum leaks. I've checked the TPS and it's fine... haven't reset the IAC / minimum idle yet, but if anything it's idling slightly higher than normal.

Timing wise, I'm 100% CERTAIN that I put the distributor back in the exact same way it came out... being my first time I was very careful with marking the position of both the rotor and the base. However, initially it did run like crap and when I checked the timing it was way retarded... maybe 12* or so. I've reset it to 6* BTDC.

I'm wondering if maybe it had been deliberately retarded instead of fixing something properly... I'm sure the previous owner's mech did a few very weird things so it wouldn't surprise me much.

Drivability wise the care feels fine, it's just the vibration and rough idle and the pinging.

Any ideas on what to check? I don't want to bring the timing back... if anything I was hoping to try running 8* in a few weeks time!

Thanks...
Stu

 

actually the timing was advanced, you retarded the timing,


probably vaccum leak, either a line or the manifold

 

No, the timing mark was to the right of the tab and I had to turn the distributor anti-clockwise...

The manifold shouldn't have any vacuum leaks... new gaskets and torqued to correct spec... (read: I sure hope it's not that!)

 

The slightly high idle is a symptom of vac leak. Not the only cause of a high idle, but one of them. It's most likely IMO if it rears it's ugly head near idle/low rpm cruise, but not elsewhere.

Other than that...did you disconnect the tan/black wire while setting the timing?? That'll make a difference.

The pinging could be blow-by, meaning your rings and/or valve seals are toast. Or carbon build-up on in the chambers. Were the spark plugs the proper heat range?

 

Yes I disconnected that wire for the timing...
Spark plugs are AC Delco R45TS... which is correct... although I DID have R43TS in there previously.

 

So, if you leave out all of that stuff about gaskets and filters and porting, the bottom line is, you're telling us you advanced the timing 18° (from -12 to +6) and now it pings.

Well..... ???? are you really surprised?

It's not impossible that the inertia ring on the crank damper has slipped, and the timing mark is now off in the ozone somewhere. Wouldn't be the first time. Might not be a bad idea to ACCURATELY verify that the timing mark lines up with the #1 piston EXACTLY at TDC.

Try using premium gas if you're not already.

Or, if all the rest is OK and it really bothers you, back the timing off in small increments until it quits.

 

Rough idle and pinging sounds like a vaccum leak. If you advance timing alot the engine will not run rough at idle. There are alot of places in a TPI intake to leak. Yo see, if you have a vaccum leak, then you MAF sensor is not meassuring all the air going in to the engine. This will make the engine run lean, this will make it idle rough and ping. Also like he said check the harmonic balancer for correct marking.

 

So what's the best, most accurate, and easiest way to get #1 to TDC?

Tomorrow I'm going to check for vacuum leaks, maybe with some propane... it does still sound like there might be a small leak though it's hard to tell... possibly from the cold start valve.

It's a good point about having advanced the timing by 18*, yes... but on the other hand it was running rough as guts until I brought it up at least to 0* BTDC. Then again there was definitely also a bad vacuum leak at that time too...!

Ran a datalog with WinALDL last night but forgot to save the individual data tables, though I do recall there were a hell of a lot of knock counts around 2000 rpm at low MAF readings (not surprising given I didn't give it much throttle too). I'll redo the datalog and post it somewhere for advice.

Thanks,
Stu

 

Well, I removed the plenum and runners, checked the injectors for leakage and that they were all working, replaced the PCV vacuum hose and thoroughly checked everything for vacuum leaks once back together. No leaks. Also checked the IAC and reset the minimum idle, but it's still idling high sometimes (no longer rough, just high). I think there may also have been a vacuum leak around the cold start valve and I've got that sorted out now.

I retarded the timing back to about where it was before, or possibly slightly advanced (given that I can't remember exactly where it was). Knock counts are significantly lower now (see below) with no audible pinging which is good. I'll get somewhere to check the timing against TDC for me.

There's also a datalog attached... (I know about the O2 sensor / code 44 - the new one seems to be dead so I stuck the old one back in).

Anyone care to comment on the logs?


Thanks,
Stu

Knock counts: