1991 Miata 1.6L Ignition Timing Issues

jkarlin said:

In reply to WonkoTheSane (Forum Supporter) :

I'm considering going with a stand alone ecu and figure i shouldn't even consider something like that until i can figure out the timing scenario. Especially if after a stand alone if i want to go turbo / sc there is a lot going on with timing. The picture below is before i tool it apart. Was even using the little FM tool to keep the cams from changing.

Unfortunately, that's not too much of a help, I was looking more for a head on shot without parallax.

jkarlin said:

In reply to Keith Tanner :

It runs very well when its not "assembled" correctly. I don't know the history. I bought it from a college girl who had 17in rims on it!!!! Those went away really quick. It did already have an oil cooler, oil filter relocation, and a racing beat catback. So the car had been modified slightly. Ive owed the car now for 3 years and really drive on nice days, to and from the track, and track days / autocross. Its a 91 with 125k miles. I have put 5k on it in 3 years. It doesn't even smoke when floored or smoke it all for that matter. The car has full bolt ons yet wont pull on another bone stock 1.6 that blows smoke like crazy. Makes me wonder if it is down on power? At idle i swear it almost sounds like it has a slight cam? It has a little lope however not extreme to the point where the idle is affected.

Oil cooler is an unusual mod for a college girl sort of car. This thing may have some history. Add in an uneven idle and an indication that it's down on power - it doesn't run right. I'm not sure what "full bolt ons" means.

So I would set the cam belt timing per the book and concentrate on why you either have a CAS that's off or why you can't get the ignition timing set. So that's the timing marks or the CAS itself.

Confirm the alignment dowels in the cams. Confirm, as best as possible, that they are stock cams. Swap in a known good CAS. Confirm the timing mark on the pulley is accurately placed. We've done some of this but if this was me in my garage I'd go through it all again in case I had a brain fart.

Also, I have to ask # does your timing light have an advance adjustment on it? Is it zeroed? Don't laugh, it happens...

We need to come up with some way of determining if the cam timing wonky or if the ignition timing is screwed up and we're compensating for it with the cam timing.  While not a 100% test Keith's idea of swapping in a known good CAS is a good one.

I can't remember if there are visible part numbers on the cams.  It would be good to confirm that they're correct.  There's a mod where you hack the drive for the CAS off an exhaust cam and install it on the intake side.  I've never done it so I'm sketchy on the details but I believe doing it correctly requires drilling a new hole in the cam gear but perhaps that's been done on this car incorrectly.

It's also possible that it's got some kind of cheater Spec Miata stock cam regrind in it.

I'm also curious how it runs with just the exhaust cam set off a tooth and the intake set correctly.

I don't suppose you have (or have access to) a degree wheel and a dial indicator.  Ideally, the next step would be to degree the cams so you know for sure what they are and how they're phased.

The "exhintake" swap is a 1.8 thing. The CAS drives off the intake cam on a 1.6. 

The only way the cam timing can be off is if the cams are modified or the gears are installed incorrectly. I don't think it would run in the latter case. 

I am thinking either reground cams where the centerline was changed slightly to fit the new profile under the one that was already there, or a headgasket shim for an ancient boost setup that is no longer present. Both would explain low NA power (considering stock tune on it), one would explain an idle lope. Either would be the kind of thing you might have done way back in the day when aftermarket cam and tuning options and general turbo knowledge were much sparser.

Keith Tanner said:

The "exhintake" swap is a 1.8 thing. The CAS drives off the intake cam on a 1.6. 

The only way the cam timing can be off is if the cams are modified or the gears are installed incorrectly. I don't think it would run in the latter case. 

Apparently I'm  sketchier on the details than I realized. 

I agree that it's unlikely to run with the gears installed incorrectly. 

WonkoTheSane (Forum Supporter) said:

Dumb question, but did you pull the bolt out from the crank pulley and verify that the keyway wasn't buggered up?

I did remove the bolt. The bolt and keyway were in very good shape. I actually replaced the front crank seal while I was at it and I will say I was amazed how easy my crank gear came off... I could pull it off by hand.

Keith Tanner said:

jkarlin said:

In reply to Keith Tanner :

It runs very well when its not "assembled" correctly. I don't know the history. I bought it from a college girl who had 17in rims on it!!!! Those went away really quick. It did already have an oil cooler, oil filter relocation, and a racing beat catback. So the car had been modified slightly. Ive owed the car now for 3 years and really drive on nice days, to and from the track, and track days / autocross. Its a 91 with 125k miles. I have put 5k on it in 3 years. It doesn't even smoke when floored or smoke it all for that matter. The car has full bolt ons yet wont pull on another bone stock 1.6 that blows smoke like crazy. Makes me wonder if it is down on power? At idle i swear it almost sounds like it has a slight cam? It has a little lope however not extreme to the point where the idle is affected.

Oil cooler is an unusual mod for a college girl sort of car. This thing may have some history. Add in an uneven idle and an indication that it's down on power - it doesn't run right. I'm not sure what "full bolt ons" means.

So I would set the cam belt timing per the book and concentrate on why you either have a CAS that's off or why you can't get the ignition timing set. So that's the timing marks or the CAS itself.

Confirm the alignment dowels in the cams. Confirm, as best as possible, that they are stock cams. Swap in a known good CAS. Confirm the timing mark on the pulley is accurately placed. We've done some of this but if this was me in my garage I'd go through it all again in case I had a brain fart.

Also, I have to ask # does your timing light have an advance adjustment on it? Is it zeroed? Don't laugh, it happens...

 

The cams are stock. I have a spare 1.6 long block in poor shape. The casting numbers on those cams are the same numbers of the cams in the car now. I will go thru all of this again just to be sure. In the meantime I went ahead and ordered a new CAS. I figured worst case I would have a known good backup and nobody had anything local. My timing light is adjustable, but I already went down the path of confirming it was at zero and checking that again.

This past weekend I dug into the car with a fellow miata nut who also happens to buy/sell miatas and had parts to help diag. We went through and checked several items.

With the engine where the cams off mechanically, but where the vehicle is running well we:

- Replaced with a brand new CAS. The vehicle ran exactly the same.

- Swapped ECU with another known good ECU. The vehicle ran exactly the same.

- Performed a compression test - Cylinder #1 - 185, #2 180, #3 185, #4 185

- Performed a leak down test - All (4) cylinders tested very good (in the low / green)

- Performed a vacuum test - took this reading off where the cruise control line goes before the throttle body - only was getting 15-16 .... vacuum should be 18-20? Vacuum seemed a little low, but with the cams off the way they are this could effect vacuum?

- Performed a smoke test to confirm there were no vacuum leaks. Found a pin hole in one rubber line, but so minimal.

The motor seems very healthy, but of course nothing above explains why the vehicle needs to run with the cams in those positions. 

Whats next? Swap the cams with known good/stock cams?

Does anyone have the stock cam specs?

I hate to have you fire the parts cannon at it anymore than you already have but with the tools you have you may need to do that.  If the tools were available the next thing I'd do is confirm TDC and cam timing with a degree wheel and a dial indicator.

Looking at the ignition side it might be worth confirming that the TEN pin actually connects to the ECU and that it's not shorted to ground.

I've never seen it but a bad igniter could effect ignition timing.  If you've got a known good one it would be worth swapping it in.

With the cams set where the car runs well how much does the ignition timing and idle change when you jumper the TEN pin to GND?

With the cams set by the book will it run without changing the CAS position?  If so what's the ignition timing with the TEN pin jumped to GND?

On the cam timing side can you tell if the relationship between the pin and the drive slot on the back of the intake cam in the car is the same as your known stock one?