vega7677,
Those are pretty good prices for the MFI spider! I paid $250 almost 4 years ago from my dealer so they have come down.

Captain Hook,
The hold down bolt on these is an M6 bolt (10mm head 6mm major diameter). The hole in the hold down clamp is 8mm wide & 11mm long and is at a distance of 40mm from the center line of the distributor shaft (just measured and the length of the factory hole is oriented such that it is pointing away from the distributor shaft and is of no use for adjustment purposes). The image below shows the orientation of the hole in the hold down clamp:


For 15 degrees worth of adjustment, the hole that the retaining bolt goes through would have to be slotted to a width of 17mm minimum (6mm for the bolt + 11mm that results from the trig 40*tan[15]). And as stated, there is no play in the hold down clamp to the distributor body. So there isn't 15 degrees worth of adjustment. If you want to count the 2mm worth of clearance in the hole, that would be just shy of 3 degrees worth of adjustment.

All of my references make note that the timing is not adjustable as well... On the older, pre-EDI distributors, yes, but not on the newer EDI stuff (mid-95+). On the EDI distributors, you just have to get it on the proper tooth and everything else is set from there provided there is no worn/bad parts.

 

Kyle, I respect your knowledge tremendously however, I'd agree with you on this one but, then we'd both be wrong Camshaft retard is adjusted by turning the distributor housing. It does NOT adjust ignition timing. Turning the distributor perfectly aligns the Camshaft Position Sensor, (CMP) with the camshaft so that the Hall effect switch sends the pulse to the PCM at the correct time. Correctly installing the distributor, in proper time, does not by any means, guarantee cam retard is correct. On older engines, when ignition timing was adjustable, the distributor fit rather snugly in the intake manifold bore. On 96 & newer 4.3's, the distributor housing does not fit quite so snugly in the bore. The I.D. of the intake manifold is noticeably larger than the O.D. of the distributor housing. The difference in diameter is what allows the distributor to be adjusted. Because of the differences, it is entirely possible for the distributor to be oriented away from 90 degrees from the camshaft, (distributor not plumb). When this happens, the gear on the distributor will wear off-center, very common, we've all seen it, this is what causes it. The GM "dealer issue" shop manual, and several of the high end scan tools, (Tech2, Snap on Solus, Modis, etc) explain the procedure. Takes about 10 minutes, but you need a high end scan tool to access camshaft retard.

 

So you are saying that instead of just slotting the hole which would keep the distributor gear lined up properly with the cam drive gear GM knowingly created a method of "adjusting" CMP to CKP correlation by oversizing the hole through the LIM? I know you have all of the GM SI stuff at your disposal, but this just doesn't make any sense what so ever. If true, that is quite possibly the stupidest engineering approach ever taken and one that would make it difficult for anyone to get the distributor back in properly... I must have been getting lucky all the times I put one of those EDI distributors back in...

Anyone have a LIM and a set of dial indicators handy to take a measurement? Actually, I can figure this out... Give me a bit.

*EDIT* - For this to work as stated, the bore through the LIM would need to be, at a minimum, 8.5mm (0.336") larger than the engaged portion of the distributor which is 31.5mm (1.240") in diameter. So the hole through the LIM would need to be at least 40mm (1.575") in diameter. Trig is easy! LOL

 

Who knows why they do what they do, but on this engine there is very little clearance when rotating the distributor. You really don't need much if the distributor is timed correctly. I think the most I've ever seen is 11 degrees off. I've found that when cam retard is set correctly though, the gear doesn't wear near as fast.

When they say "timing is not adjustable" it's really not entirely true. Any time you rotate the distributor, ignition timing changes. Cam retard actually does two things: along with adjusting the CMP sensor, it sets base time which aligns the rotor tip perfectly with the terminals inside the cap. *** Also, by aligning the rotor, it keeps the air gap as small as possible so there is less chance of crossfiring in the cap. And yes, incorrect cam retard can cause random misfire and usually does not set the DTC.

*** Ever look at the terminals in the cap and notice they are not burning on the center of the terminal? Incorrect camshaft retard is the cause. Placement of the terminals can vary slightly from different cap manufacturers, this doesn't affect cam retard but it can affect base ignition timing.

 

So by this information, does that mean that a CASE relearn can only account for +/- 2 degrees of separation between CKP & CMP readings?

My AutoEnginuity actually does show cam retard, but I've never had to use it.

 

Interesting conversation. But I've recently did my distributor on my 95, and was confused with the -20 degrees ignition timing my scanner was seeing. I knew that at idle ignition timing was supposed to be 0*. So I purposely left the hold down loose as I turned the distributor left and right and watched the scanner. As it would move ignition timing the PCM quickly reset the ignition timing to -20. Not until later did I realize that with a timing gun the crank is 20* advanced resulting in the PCM correcting ignition timing to see 0* at idle.

The old distributor that came out of the car had the slot that was lined up on a pin that stuck out of the lim. The new one from the parts store didn't have the slot. I guess what I'm trying to say is no matter how much you turn left or right the PCM corrects for it.

 

Kyle,
Went out this morning & checked the injector pins on the connector , none bent or out of shape. Right now I am running Seafoam in the fuel , letting it run for awhile & then letting it sit for a while.
If nothing happens today or tomorrow it looks like I'll be spending $210 bucks Monday morning !!

 

Having a brain fart on the "CASE relearn" (Not an acronym that GM uses.) Please enlighten me

I know what happens when I "assume", but here goes...
CMP retard has an immediate effect when you adjust it. There is no special relearn procedure necessary or required. If it's off far enough, say 10 degrees, you will notice an immediate improvement in performance after it's corrected. There's nothing in the shop manual regarding how many degrees the PCM will compensate for, but if it's more than it can handle, it will set a P1345 and illuminate the SES light. Past experience proved it's more than 11 degrees though You're the trig expert, maybe you can figure out how many degrees one tooth off calculates to, 'cause that will absolutely set the DTC. That would at least give us a "ballpark" idea.

Troubleshooting an occaisional misfire or slight stumble can really throw you for a loop if CMP retard is off. It can cause a random misfire and not set any P0300 series DTC's or record any data in the misfire history file. Crossfire in the cap can be so subtle and infrequent and the CKP and CMP sensors detect it, but the way the PCM is programmed for misfire sensitivity, it doesn't acknowledge the data as a misfire. The farther off CMP retard is, the more crossfire is encountered which will eventually cause plug fouling and shorten the life of the distributor cap. At this point, the damage is done and the PCM will set P0300 series DTC's.

 

CASE relearn = crankshaft variation learn.

There are 13 teeth on the distributor drive gear. No trig involved in this one. 360/13=~28 degrees.

 

LOL, good job! Never counted the teeth before, My guess would be it sets P1345 DTC at anything in excess of 24 degrees +/-.

The crankshaft position system variation learning procedure is used to calculate reference period errors caused by slight tolerance variations in the crankshaft, the crankshaft tone ring, and the CKP sensor. The calculated error allows the PCM to accurately compensate for reference period variations, (misfires). Bottom line, it calculates exactly where the crankshaft is in rotation, (much like what the CMP retard adjustment does for the camshaft).

The CKP relearn must be performed if/when any of these items are moved, removed or replaced: The CKP sensor, the front cover or bracket holding the CKP sensor, tone ring, (vibration dampener), crankshaft, engine block or PCM.

Something to keep in mind about CMP retard: Over a period of miles, the timing chain stretches and will have a direct affect on CMP retard. It will not affect CKP data stored during the relearn, but a stretched chain could cause misfires to set because of the excess slack in the chain. As I mentioned earlier, if the vibration dampener/tone ring is removed, (during timing chain replacement) the CKP relearn must be performed.


EDIT:
Originally Posted by swartlkk
So by this information, does that mean that a CASE relearn can only account for +/- 2 degrees of separation between CKP & CMP readings?

CMP retard is how many degrees of rotation the camshaft is off from crankshaft position. Obviously, if CKP relearn data is inaccurate, CMP retard reading will also be inaccurate.