SBC Timing - very odd, how is this possible?

[toyotaspeed90]

What if you got the other side of this problem and discovered you were the first?

If that were the case, then it would have rotated exactly 180 out to where I caught it first, then rotated out 180 exactly again.

It's either - it slipped at exactly 180 out multiple times (have a hard time believing, since even 20* variance either way would cause horribly bad running... which is only a 4% range variance of the possible 360 rotation) or something else is going on...

Any progress? I had an issue where I thought the balancer had spun. I used a TDC tool in the number 1 plug hole then rotated the engine each direction and put a mark on the balancer at the TDC pointer. Halfway in between the two marks is TDC. Mine was right on the factory mark. Could your timing light be failing?

The light is fine... it was new about 10 years ago, and though it has gotten a bit of use, it isn't "well used" at all. Timing in the 80 series and my ae95 were done with the same light and are spot on.

No progress.... I spent some time removing rust and doing unpleasant 40 things by covering holes up with diamond plating...

Did drive it last week around the neighborhood before heading to Ocean Shores for the weekend and it drove great, no overheating.

 

[SuperBuickGuy]

it's because it's 180 degrees off that has me thinking slipping. The ring is drilled for balance so one side is going to be lighter than the other.... thus it'd be in only A position or B position. However, as I've said before, I don't see it so I dunno - it's a long distance guess.

 

[toyotaspeed90]

Decided to buckle and buy amother balancer.

It's attached to a TBI 305.... the carb and timing issues put me over the edge, time for EFI. Either the gas gauge is off and it's getting about 2mpg, or the fuel pump is going out. (Something is up with the carb, though, since I cant get any vacuum changes when adjusting the idle fuel screws). The plan has always been to EFI it... now I just happen to have extra parts (longblock, stock in frame headers if I decide to move exhaust inboard, serpentine system, remote oil filter.... and a T5 manual with 4wd transfercase... for s***s and giggles).

Think I will minimize down time by getting an adapter first... so I can test/wire the tbi on the 350. It was originally from a 91 Camaro, but had been put into an S10, and said they originally had an issue with needing some resistor to bypass the expected key to keep it running....

 

[srgould41]

Too bad you are so far away or I could help out. I went through the TBI mod on my SBC. Took a while to perfect.

 

[toyotaspeed90]

It *shouldn't* be too difficult for me.... I helped a friend (and by that I mean I did 90% of diagnosing why it wouldn't work, which took him weeks and me minutes) convert his 78 K20 to TBI, and I've done several Megasquirt 4 cylinder cars....

 

[srgould41]

Nice.

It *shouldn't* be too difficult for me.... I helped a friend (and by that I mean I did 90% of diagnosing why it wouldn't work, which took him weeks and me minutes) convert his 78 K20 to TBI, and I've done several Megasquirt 4 cylinder cars....

 

[toyotaspeed90]

Spent an hour going through what I had and am annoyed.... just a few things missing so far (and haven't been able to identify a few plugs yet, partially because oil/grime and age have recolored the wires for me) like map sensor, spark control, AIT... oddly enough the O2 sensor and connector are there but the harness side seems to be MIA (not an issue, just an 'uh, ok').

TPS sensor is missing and has me a tad intrigued. I expected the small TPS with the round connector (which online is stating is the accurate sensor for a TBI Camaro) but the connector is a flat connector and the parts stores list that as the Z28 (port injection) sensor.

 

[srgould41]

I ended up purchasing some replacement connectors for my harness to fix broken ones. You may need to do the same. Your harness might not have been the one connected to your other parts.

 

[toyotaspeed90]

That is true and I have no problems with that...

The AIT seems to be eluding me. I've gone through every wire on the harness and labeled everything needed. Looking at diagrams the AIT is supposed to be on a specific connector and a tan wire - the wire there is blue and runs to a very odd little box, almost like it's some aftermarket BS chip.. but that wouldn't explain the wire color difference.

Will get some photos here soon....

 

[toyotaspeed90]

Pulled apart and marked up (usually don't do this with toyota harnesses, but not as used to these)

The odd little box....

Showing I'm not quite as nutty as it seems.... ECU pin C12 is blue, not tan (as indicated on the paperwork), runs to the small connector, then directly to the box on the right:

I may need to see if there are varying TBI diagrams - because the pinout shown here is ever so slightly different than a diagram I have (mainly in some AT vs MT)... and there are 2 wires indicated as "not assigned" but have wires coming out...

 

[toyotaspeed90]

Things are starting to become more clear - not overly happy though as I could (should) have just spent a little more to get a running vehicle to scavenge from.

The setup was swapped into an S10 who knows how long ago now. It came with 2 ECUs... after digging though numbers, one is an S10 2.8 V6 ecu. The dizzy I was given is also not a V8 unit, but is definitely TBI. I've also determined that the TBI harnesses are very similar and pinout are essentially identical with a few wires here and there that are different.

The harness has no air temp connector nor wiring, but has a knock sensor. This was throwing me off because the V8 systems either had both or none.... however the 2.8 had a knock sensor but no AIT....

Meaning - the harness I have is a weird hacked up 2.8 harness that was somehow worked onto a 305 (LO3), and was done so that the S10 body harness didn't have to be modified.

I'm also pretty annoyed that the parts were misrepresented (missing several EFI pieces though described as 'complete', after getting my hands on the trans - was told it's an S10 unit, but has a 10 spline input shaft - which was only on the manual ASTRO vans..
Either way really shouldn't have ever been put behind a V8 as the ASTRO units aren't world class T5 transmissions). I'm partial to blame because I didn't take the added 20-30 min at his place to go through the boxes of parts.

The injectors weren't working at first - had to work on them a bit, but thankfully they seem to be OK now.

I'm on the verge of just ordering an MSD PCB 3.0 and the needed dizzy.... the difference in price of it and the missing parts is only about $100 at this point, and the harness is already 1/2 way hacked up by the PO....

 

[Mace]

$100 to start with a fresh system sounds like a no brainer to me. And I'm a cheap bastard!

 

[toyotaspeed90]

Contacted the seller of the parts - lo and behold he 'found' many more parts... including 2 more harnesses, many missing pieces, another ecu, and more.

I have to go through this stuff to figure out what I even have now....

The price for MS hasn't changed, but the situation has.... I have a feeling I'll have a tough decision soon...

 

[toyotaspeed90]

One of the additional 2 harnesses had the same small box, only this time bolted to an ECU.

So it is factory.

Little digging.... as it turns out (and actually finding info for this is oddly difficult because even guys at the forum who work for GM question it's existence) it is a "ETM" or an 'Elapsed Timer Module' - where it controls the cold start of the vehicle for the first few seconds of running.

This kind of makes sense - that Chevy would trick their own computer into seeing a strange value in place of the AIT to increase or decrease fuel at start up (remember above how I said that harness had no AIT, but the input for the ait ran to that box?).

What's strange, though, is the new harness is definitely more complete (haven't gone through it... it's about 3-4x larger than the one posted above), is supposed for the 305, but can only find reference of the ETM for the 2.8.

I also 'get' to play with VATS.... yay.... I've read it disables cranking (easy to get around) and fuel (I'm guessing that doesn't mean fuel pump)... supposedly the harness has the proper resistor in place already...