Performance 400 is in the truck now - CHI heads, Comp cams 265DEH, TMI pistons, bored 20 0ver, balanced and blueprinted, etc. Everything is sweet except the Crane cams digital distributor and control box. The Distributor WON'T hold a setting. Timing gets set and then it fluctuates all over the place. Anybody else used this set up with similar problems. Was quite a bit of money for a system that won't hold a setting properly.

 

i'm just curious how the vacuum part of the Crane deal works, what did you have the vacuum hose connected to?

 

According to the "chief" Crane Tech, the vacuum line should run from the distributor to the manifold vacuum outlet on the Edelbrock carb, contrary to the Crane manual instructions to connect to port vacuum outlet.

 

any updates on this system?

 

that's what i've heard before too, contradictory information. if it's a MAP sensor, it should reference manifold vacuum i would think? i have always thought that ported vacuum was ported venturi vacuum but recently read in a post that it's ported manifold vacuum. i never used ported vac and never checked it out either so now all i can say is that i need to check it some(warm) day. did you try different vac sources? are you sure that the control box isn't confusing your timing light? MSD confuses the fancy timing lights that have fast recovery time, they pick up the multiple sparks instead of just the first one.

 

A MAP sensor can measure any vacuum source, it just so happens it is named Manifold Absolute Pressure sensor on some vehicles.

From what I understand about that Crane system it uses manifold pressure.

The ported vacuum signal should more accurately be called venturi vacuum. It varies with speed and load. I prefer to run manifold vacuum and leave the speed part of the advance equation to the mechanical advance.

 

What is your idle vacuum? Is it steady? Have you tried disconnecting it and observing the timing for a consistant reading?

 

Idle vacuum fluctuates between near zero and 8, and unless RPM is increased to 1,500 or more to get 15 inches with no load, the engine stumbles and dies with vacuum at any setting including zero connected to manifold or port or even disconnected altogether.

The mechanic here in Salt Lake City has no experience with the Crane digital ignition and, according to him, the Crane ignition is a piece of s***, so I bought a simple Accel distributor and coil he understands so I can get my truck on the road to my new home in Mobile, Alabama, where I hope to find a shop that can set up the Crane ignition properly.

This is the same mechanic who removed my new Motorcraft 92 degree thermostat and replaced it with a Carquest 85 or so degree unit - only one they had apparently - and claimed I don't know anything about thermostats for Ford 400 truck engines when I told him he installed the wrong one and I would prefer to have my Motorcraft thermostat reinstalled.

 

sounds to me that you can do much better by yourself rather than with the help of the Salt Lake City M'cJagnic?

manifold vac at idle should never fluctuate to near zero. you either have a leak, valves are not closing/sealing or you are measuring something other than manifold vacuum. manifold vacuum is the standard source that is measured at or near idle.

i'd start by checking for vacuum leaks, Torque 1st suggested using an unlit propane torch, just open the valve on the torch and guide the propane gas near all the gaskets and hoses, anything that is connected to vacuum like the brake booster, trans modulator and line, charcoal canister, etc...

then i'd do a compression test or cylinder leakdown test to see what's going on with the valves.

whatever you do don't pay that M'cJagnic another penny, it'll be more expensive than it's worth to find out what he really does know about, if anything. find out if you're near anyone in your regional forum here that can wrench and/or ask any questions here about something you're not familiar with.

 

A shakey low vacuum gage usually means something is wrong in the valve train. Did you check push rod length ?

 

All of the valve train parts were supplied by Tim Meyer to work with the CHI heads on a 400 - roller rockers, lifters and push rods, etc. Tim also supplied the Comp Cams 265 DEH cam. Mr. Know it all mechanic who is doing the work here in Salt Lake City degreed the cam to 4 degrees positive - the proper way to do it according to him - despite the fact that everything I've read in this forum says to degree at 0 degrees straight up.

 

call the comp tech line and ask if your cam has the 4* already in the grind, most do. merely installing the timing set at +4* does not constitute "degreeing". degreeing means checking and making necessary adjustment to verify that the cam is timed to the crank as the cam card specifies. sometimes the is error/variance in the machiing of the crank keyway, timing set and cam dowel hole, degreeing corrects all of these chances to be off a little.

there is a chance that your rockers may need to be shimmed for proper lifter preload. too much preload can hold the valves off of the seats and cause your vacuum irregularity. i can't say for sure that this is the case from way over here, but it should be checked out. a failed compression test will lead you to this step.

 

Find another mechanic.