first question has any one done this? what are the advantages of going to a mechanical advance?

im interested in doing this since the timing on my car keeps goin up and down 4 no reason, i checked everything that has to do with timing, its a new crate engine with a comp cam i replaced the distributor, knock sensor, checked tps and iac, checked timing chain and everything seems to be in order, the only thing i can think of is the computer doing it, so thats why i wanna go to a mechanical advance, so that the computer dsnt have anything to do with adjusting the timing.

please correct me if my thoughts are wrong or tell me what is involved on doing this. thanx

my car is a 92 z28 5.7 tpi


EDIT: I CHANGED THE TITLE, AT FIRST I WANTED TO SWAP MY DIST TO HEI

 

The timing or the idle?
How do you know timing is changing?
With the engine changes you probably need a custom tune?
The stock tune on works so far especially on MAP cars.

How big is the cam?
The computer is probably trying to get the stock idle speed that the cam won't let the engine run at so it is adjusting the timing but not getting a result

 

well, the idle i know im not gonna have it steady bc of the cam i know its the timing because the timing mark jumps up and down checking it with the timing light


here's the cam specs

 

ttt

 

Do you have the spark (EST ) control wire disconnected when checking timing?
If you don't you will see normal computer operation as the it adjusts the timing .Can only check timing with wire disconnected

 

yup is desconnected while im checking it

 

In that case you have other problems because when wire disconnected there is no computer control of dist and timing should be fixed at the static timing from where you put dist in

 

why would the timing be jumping up and down to try to adjust it?
so then converting to hei would solve that problem right?

i dnt think the cam is hot enough to need custom tunning is it??

 

bump

 

changed title, hope is more descriptive

 

ttt

 

If you have the correct wire disconnected there is no connection to dist to let computer move timing.If timing is not on the mark then something else is doing it.
How many degrees is timing moving at idle when you put timing light on?

You can't run a regular HEI on a EFI setup because the computer takes reference signals from the dist for it's adjustments .
First up it wouldn't start because computer needs to see a reference signal from the dist when cranking before it will fire the injectors

Correct

 

When checking base timing with the timing wire disconnected (tan wire with a black stripe going through the in-line weatherpack connector that sticks out of the main wiring loom above the heater box) it should be steady at whatever you have your base timing set to. If it's moving around there is a MECHANICAL issue somewhere in the motor. Like a worn distributor gear or a cam that's "walking" front-to-back in the block (for example, a factory-style roller cam without the cam retaining plate properly installed), or the mag pickup ring inside the distributor isn't screwed down tightly (which would be extremely odd).

The factory computer-controlled distributor has NO advance mechanisms built into it. All advance above base timing is determined by the computer. When disconnected from the computer via the timing wire connector it supplies a flat timing curve (no advance under any conditions). If the timing is moving around under those conditions there is probably no other possible explanation besides a MECHANICAL issue.

Remember that the distributor gear and cam gear mesh at an angle to eachother (helical gears). If there is any movement of either one up and down or front to back it will change the timing.

My experience is that even a severely worn timing chain will only cause about 2* of float. Given that you are seeing double that amount it's not likely the timing chain.

 

ok now lets say that it dsnt jump with the wire unplugged but as soon as i plug it in it starts jumping, what will be causing that to happen? im gonna check it tomorrow but i wanna have an idea for now.

 

It's supposed to jump when the wire is connected - that's the computer changing the timing for the conditions that it's getting via the other sensors.

EST wire connected = timing jump
EST wire disconnected = NO timing jump

Is the car running bad, or are you just panic stricken about the timing changing on it's own?

 

the car is running crappy, when i set the timming where its supposed to be, when it reaches normal temp it will rev up and down and then stall, the fix for that is that i have to advance the timing by turning the dist, the problem with that is that when i get to a complete stop and i step on the gas to go the car shuts down, it starts right away again but every stop does the same thing.

 

For starters you are doing that wrong.

Need to set IAC and TPS 1st because that is what adjust the idle .The timing is just following along as the computer " tries " to get idle right

http://www.corvetteactioncenter.com/...and+Idle+Speed

then check for vac leaks

 

tps is at .54v as suggested, idle speed however i wasnt able to set it up as suggested bc my rpms are goin up and down so i just had it as close as possible(i believe is due to the cam installed). checked my timing mark again and it jumps 6 degrees up and down(from -6 to 0) with EST wire disconnected, if i leave it like this, the car stalls after i plugged the EST wire . now if i want to keep the car runnin i have to turn the dist to advance the timing with the EST wire plugged in, but when i disconnect the wire with the car running, my timing shows that is at 10 degrees AFTER TDC wtf, lol anyways, the problem with this is that if i come to a complete stop as soon as i open the throttle the car shuts down

 

I'm no expert on a TPI car, but timing as I know should always be BTDC, not AFTER. If it were me, I'd disconnect the EST wire, loosen the dist hold down, and twist the distributor about 1/16th of a turn clockwise (which advances timing), and then see if I can get the car to start - maybe slightly less. Have someone turn the car over while you turn the distributor ever so slightly in that area until you can get it to start and run, then adjust timing to spec. Then reconnect the EST wire and see what happens. Also, keep in mind that BTDC is to the left of 0 on the timing tab when looking at the front of the motor.

If I'm dead wrong here someone chime in - but I've never seen any induction SBC that was supposed to set to anything AFTER TDC.

*edit* After re-reading your first post, I see it's a new engine and you replaced with a new dist. Are you sure you stabbed the distributor with the crank at TDC on the COMPRESSION stroke?

 

yes im aware i should be at btdc thats why i find it weird lol, and yes i know for sure i set it top dead center on compression

 

bump

 

If you disconnect the est wire and set the timing and make sure to lock it down good it is physically impossible for the timing to jump unless there is mechanical damage. Do a search for surging because thats your problem. Make sure theres no vacuum leaks, ohm your injectors and check the fuel pressure and if theres a problem with the charging system you need to fix it.

 

that was the first thing i looked for, no vac leaks, ohm on injectors and pressure is normal, i also bench tested the alternator and everything is within normal specs, anything else i should look for before i tear my engine apart??

 

bump

 

Are you sure you got the cam timing set correctly? Also, check your injectors. As stated above, your TPI motor will not run without the reference signal from the EST distributor.

 

what do u mean the cam timing? u mean the marks from cam and crank align? if so, i haven't checked that, i didnt installed the cam, i bought the engine with it installed... do u think thats what is causing my timing to jump around?

 

You say that it seems to run best at 10 degrees ATDC. This would cause me to wonder if the cams not off one tooth. If you could degree the cam that would tell you for sure.

 

hmm! ill get into that once soon as i get a cam degree kit, now will that also cause the timing mark to jump up and down 6 degrees with the est wire disconnected?

to illustrate more n help u guys help me, here's a better description of how the mark jumps:
,steady,steady,steady,steady,steady,jump,steady,steady,steady,jump,jump,
steady, steady,steady,steady,jump

is basically a random jump

 

Few things first you said you replaced the distributor what did you replace it with a stock replacement i hope? Second if and only if it was a stock replacement or its equivalent the timing should be controlled solely by the ECM. Assuming you in fact have disconnected the EST there should be no movement in your timing. Now since there is you may have a bad ignition module thats falsely triggering, you may have plug wires run too closely together inducing voltages in adjacent wires (cross fire), you may have a bad timing chain, a bad distributor gear, You may have a bad connect in one of several places, even a bad timing light. Theres a whole multitude of problems you could have but simple stuff first make sure you have the right distributor, the EST is in fact disconnected, check you plug wires to make sure there is ample spacing and no damaged insulation, try another timing light, check all connections especially! That includes grounds in the distributor!

 

MAN thanx for that list lol... yes i replaced the dist with a remanufactured one now what caught my attention is that i do have the plugs wires touching each other (MSD's 8.5mm if it matters) , i do have the est disconnected and checked it with 2 different timing lights... will my wires touchin cause the random jump with the est disconnected????

 

Its possible. The thing is any current that flows through a wire generates a magnetic field. The rapidly expanding and collapsing magnetic field can induce a spark in adjacent wires if routed too closely much like how a ignition coil works. Also if the insulation were to be damaged at that point obviously that could cause a problem. So ide definitely space them out a bit. Install the plug wires in their factory wire looms or get some aftermarket ones. I would shoot for at least 1/4 inch spacing between wires.

 

Check your coil. I had the same problem. I could not get my timing to stay put. I checked nearly every sensor. Changed the distributor (it needed it anyway). I even put the spark light (I don't know what you call it, but its a little tool that goes between the spark plug and wire to check to see if the plugs are getting spark. I couldn't find the issue. Took it to a shop and they diagnosed a bad coil. Swapped in a new coil. Problem solved.

 

my ignition coil is new and i ohmed it and its how its supposed to be.

 

separated the plug wires, no change, timing still jumping.

 

BUMP

 

basics....start with base engine and see if everything is ok there, like others said with the cable disconnected timing is mechanically controlled...create a basic map or a power flow of some sort...from crank to cam,cam gear to distributor gear,distributor gear to shaft, coil to rotor, rotor to cap, cap to wires, wires to plug, wire to timing light, and timing light to mark on harmonic balancer....now somthing isnt right in that basic flow and has to be checked.....you need to check cam, whats its relation to the crank, was it installed correctly, how much play does it have, is it walking back and forth, was it broke in correctly, did the cam get ground down, is the gear ok, is the distributor gear loose or damaged, how is the electronic pick up in the distributor, cap and rotor in good shape, wires ok, plugs icorrectly gapped, are you attaching timing light to cyl#1 wire, does it have the correct harmonic balancer, is the mark in the correct location, is the balancer damaged?......those are the basics i would follow and make sure are ok before i start stabing electrical wires and modules....good luck.

 

I've read the post, page up and down but can't see any post on cam timing. What's a crank align?

 

post 25 and 27 by ASE doc

 

I'm having this exact problem, timing not stabile with EST disconnected. Could not find a final solution in the thread.
Have changed coil and ignition module, didn't do anything. Car runs quite bad most of the time. I have had the car for three years, working fine all the time until now. 350 Tpi engine.

 

how much slack in the timing chain ?

 

This thread is 13 years old. You probably should start a new one, and this time more details about what led up to your issues. Running fine for years and suddenly NOT running right is NOT typical of a timing problem.

Or just fire the parts cannon at it. Everyone enjoys doing that.

 

Well ....I have found recently a possible Problem with same symptons.

305 tpi flat tapped cam
Timing was jumping all around while est was disconnectet

Timing chain good condition same as the Distributor gears

BUT

Flat cams have no Thrust button in front for horizontal positioning. the cams are tapered to force the camshaft inwarts the Block until front camgear bottoms out agains the block.
THIS surface was broken in badly.... almost 2-3 mm.....possibly to lack of oil

Now at this point the camshaft will travel far enought to let the timing chain canting due to diagonal pull. chain pulls the camshaft out ....the taper pulls it in ...Timing is jumping like hell

PS: if its a Roller please check camshaft thrust .......exessive play leads to jumping timing