Dyno mystery. Need your help

[dvallis]

So who is actually running mechanical advance to make more power? How many degrees and with what cam? I'm running a 284/272.

Let's hear a roll call.

[digger]

Glad you found it and it was simple. funny because I have a cheap Chinese adjustable timing gear (even the +/- marks are labeled backwards) and it's worked perfectly for years.

To be fair ive used my Nuke trouble free for the last 13 years and done at least 4 or 5 adjustments without issue (touch wood). It wouldn't be hard to design something better though. Moving around the cam was well worth the admission price from a power/torque improvement.

[nando]

Glad you found it and it was simple. funny because I have a cheap Chinese adjustable timing gear (even the +/- marks are labeled backwards) and it's worked perfectly for years.

[dvallis]

I -thought- they were properly torqued but obviously screwed it up. :-/ Nuke Gear is going in the trash. Back to stock.

Compression test after re-establishing timing will tell us if the valves survived. We had something like 0.125" p2v. Fingers crossed.

[digger]

are you sure those bolts were properly torqued ?

also the lack of a washer under the central cam bolt should be rectified IMO as the bolt head doesnt have a big flange and high grade bolts onto AL is a risk of relaxation/loosening without a washer or lots of contact area

my guess (iirc its a 272 lobe and aftermarket deeper reliefs) is that you should be ok based on the exh valve to piston clearance is normally shedloads

[Nader393]

Surprised by the lack of locking washers (serrated belleville type) under those screw heads. Do that in addition to thread locker if you decide to keep that pulley (I wouldn't keep it, if you're back to stock gasket thickness). Hopefully that pinging sound you described wasn't your valves making contact with the pistons.

[dvallis]

It was #1. Frigging adjustable timing gear threw a bolt and clocked to the stops

[nando]

FPR failure?

[dvallis]

1. Nuke timing gear slipped?
2. Injector stuck open
3. Compression
4. Leak
5. Fuel pressure
6. Spark plugs
7. Plug wires

We'll be looking into all this. Still VERY frigging weird for the engine to suddenly go stupid rich

[Nader393]

Check for spark. Was a spark plug wire dislodged while setting up the dyno? And why would it ping if AFRs are rich?

[digger]

Compression check, leak check, timing check, fuel pressure, oil pressure ?

[Old525i]

Usually, the cause of a problem is very simple. #1 seems to make sense: if the timing gear slips, it could be the reason for backfiring.

What does "VE table is WAY low. In the 30s" mean?

[dvallis]

Car was running 100% when we pulled into the dyno garage. Ran great, idled great. Once it was bolted to the dyno, in neutral, BEFORE any pulls, -something- happened.

What The F?

Idle dropped from steady 1100 RPM to ~900 and stumbling

AFRs went rich

VE table is WAY low. In the 30s

Car would not make low end power

Tuner could not add timing without getting ping

It backfired a couple of times. Never did that before, ever

Nothing mechanically obvious (rattles, bangs)

MAP & boost hoses all good and tight

What in the frigging he'll could have happened? Maybe:

1. Nuke timing gear slipped?
2. Injector stuck open
3. ?
4. ?

We're going to check 1, 2. Then test compression. I'm damn mystified. Any ideas?