Here is something real strange. About two weeks ago I dyno a Tims (TheToys) car which made 500 RWHP that day. Today we checked it again because Tim had some issues at the track. The engine only made about 388 RWHP

So further investigation showed that we were getting a huge amount of timing retard. I thought because we had switched to a small diameter F body type distributor that we had a problem with it. I changed the module, swapped the pick up coil leads, even got a brand new distributor. Nothing worked, we still got retard. I then disconnected the EST circuit from the FAST ECU, only the spark reference was connected so that the FAST ECU can run the EFI side. Even with that I got retard.

With me watching the timing and Tim driving the car on the dyno I see as much as 20 degrees of retard from a max 34 degrees of programmed advance. I see on the timing map that the ECU is commanding that timing but I see it retarding the timing with a timing light.

I am thinking that it's a mechanical problem with the cam walking forward. This is a DART Little M block so there is no provisions for a cam retainer plate like a late model GM Roller Cam block. It has to use a button on the cam nose. Jeb is tuinking along the same lines as well. He told me of a time when he had a timing chain do something very similar.

Any one got any ideas as to where I can look further. Tomorrow or Sunday Tim is bringing up his original distributor and I am going to check it with that. If its still doing it then Tim is going into the engine.

 

What is the knock sensor reading?

 

Knock sensor system totally inactive. The EST system was also disconnected. Only the spark reference going to the ECU was in place in order for the ECU to fire the injectors.

 

Does the ECM use the EST to retard the timing? Or does the knock sensor report directly to the ECM. I think that has changed over the years, which you didn't mention. Have you checked the end play in the distributor shaft?

RACE ON!!!

 

20 degrees is a ton with the knock retard function disabled.

I don't know the specifcs of his setup, but here's where I'd look:

For the 86-89, the lead colors of the pickup coil and the ignition coil have to match; it's a polarity issue. Don't know if this applies to his engine, but I'd check to be sure.

Over time, those wire colors can become hard to determine (color fades), but one thing I do is check to see if the P/U coil wires cross, if they do the coil wires should too. If the P/U coil wires run parallel, then so too should the coil wires.

A yellow coil wire has to have a yellow P/U coil wire a the "P" connector. If the coil has a white wire the P/U coil can't have a yellow wire at the "P" connector. All of that may not be an issue since you're probably running matched aftermarket components.

I'd first check to see how much back lash there is between the distributor gear and the camshaft gear. You can get an idea by removing the cap turning the rotor by hand.

I'd then pull the distributor and check the end play and the teeth on the gear. You should be able to see how well the distributor gear is indexing with the cam gear. Sort of like checking a ring and pinion install.

My next thought is cam walk. Some blocks are front walkers and others are back walkers.

Unfortunately, checking that involves tearing into the engine. I'd pull the timing chain cover and look at the inside. If it's a front walker, you'll see it, sincethere will signs of the bumper riding against the inside of the cover.

I think you already know that in order to measure the actual fore and aft movement of the cam calls for pulling the intake. UGGGGH!

I always use the roller thrust button and not the solid one. I've seen solid bumpers drill a hole in the cover.

A stock cover is notorious for flexing because it's so thin. So with a front walkers, the bumper could actually be causing the timing chain cover to baloon forward. There are a few different fixes for this;

One involves welding a piece of metal in the center of the cover aligned with where the bumper would hit.

Another one is to install an adjustable bolt nut arrangement between the cover and the water pump to brace the cover. Some water pumps have this feature.

Another one is to move to a heavy duty cover which is much thicker, like those sold by CompCams and Crane, etc. I set my cam end movement to .004 using CompCams covers that have a hole for installing my dial indicator. Install everything, then force the cam rearward. Install and zero the indicator, the force the cam forward and check the indicator to see how much it move. Grinding the roller button or washers behind it allow for the needed adjustment.

While in there you should also check the condition of the timing chain for excessive slopppiness. Drilling a .030 hole in the cam boss at 12 o'clock supplies pressureized oil to the chain to prolong it's life.

I'd check that the crank gear has been fully installed on the crank snout; if not the chain won't run true. This could pull the cam forward.

A back walker will show signs of wear on the block surface where the cam gear has been riding against the iron block. A three piece Torrington bearing takes care of that.

Some sets come machined for and include the Torrington bearing so machining the block isn't required. Back in the old days, before those were available, I had to have the block machined for that bearing. I always use both, (bumper and bearing) even on a non-roller cam setups.

Oil pump puslations can cause erratic timing fluctuations, but the readings generally just jump around, not retard the timing 20 degrees.

I'm guessing you already know all of that stuff, but that's all I can come up with right now.

When you find the cause, be sure to let us know.

Hope this helps.

Jake

 

Yes, the EST would normally take care of all the electronic spark timing functions. But in my case in the process of diagnostics. I have totally isolated the EST from the distributor. The only signal that I am using is the REFERENCE signal and that is because the FAST ECU requires that to fire the injectors. The distrbutor is basically locked down without any way to advance or retard from any signals from the ECM. From what I see the only reason I can find for what is happening is something mechanical. And that mechanical reason I beleive is a cam that is walking forward. Not sure how much because I can't move it while the cam is under load. Which means a tear down to see. I would have to remove the intake, loosen all the rocker arms and then see if it moves forward.

 

Thanks Jake, I think after tomorrow morning I will know more. We are going to try a couple other things in the morning.

 

Well this is totally weird. I reinstalled the stock HEI distributor. Now instead of reatarding it advnaces the timing a few degrees! I did notice that the wear pattern on the distributor gear was different than that of the new MSD unit. Not even sure what is causing that other than the difference in the way the two units sit into the block. We dynoed it again and we got a huge surge in power as compared to the small diameter cap distributor. Which makes sense seeing that we got our timing back again. But its not quite right and we have issues with it running on the Digital 6 box as well. Tomorrow is another day, I plan on double checking the distributor, make sure of any shaft end play and replace the coil as I know the coil is from an old truck that was laying around. There was a highspeed miss which later was taken care of with a gap adjustment. AFR looks pretty good sitting steady at 12.2 or there abouts throughout the RPM range.

 

Then my thinking is that if the stock HEI gives back the power, but the MSD arrangement kills it, it's got to be something with the MSD setup.

The old truck coil is the first place I'd look. I'd be sure to get a new one that is specifically designed for the rest of the ignition setup.

Keep us posted.

Jake

 

Tj....sent you an email a few days ago....

On the subject....what type of gear is on the cam? Everwear Gear?

Or one that he has to use a bronze gear on the distributer?

Several things can cause the timing to change. Cam play is first and foremost.

How much is the distributer engaging the cam gear? It may just be skipping along it, but you should see wear.

The pickup in the distributer could be bad, but that should have gone away with the distributer change.

And lets not forget about the timing light itself. They can be off/flakey, as I found this weekend when I used a buddies "VERY GOOD" light compared to my JUNK one.

With the ECMs disconnected the timing should be there on every check. If its not, then its definately mechanical.

What type of cover does he have. We are running the comp cams cover with the builtin roller and adjustable end play screw. You set it at zero lash, and the heat expansion give a few thou clearance.

PS: Let me know if you got that email I sent you.....Thanks.