Help with ignition Timing

[Lscobra]

My 94 recently developed an issue with sluggish acceleration under load until about 3200 rpm on the tach. At that point it picks up and starts pulling like normal. I replaced my cap and rotor because they had some corrosion on the terminals. I also replaced the Tps thinking that it was bad. No change after that. I checked timing with the brown wire disconnected. It didnt want to run that way, revved really choppy until about 3000 rpm. Would clear up and run great after that but I noticed that the timing mark on the balancer jumped probly 10 degrees every time that happened. I thought that the brown wire being disconnected stopped the timing from being changed except by rotating the distributor. Am I missing something here? Has anyone ever had an ICM partially fail and cause these issues? Thanks in advance.

 

[thx1138v2]

I didn't have any problems timing my '94 4.3L with that wire disconnected. It was rock steady on 0 degrees when I set it. Being a '94 and with it jumping around you might need a new distributor.

 

[L31MaxExpress]

My 94 recently developed an issue with sluggish acceleration under load until about 3200 rpm on the tach. At that point it picks up and starts pulling like normal. I replaced my cap and rotor because they had some corrosion on the terminals. I also replaced the Tps thinking that it was bad. No change after that. I checked timing with the brown wire disconnected. It didnt want to run that way, revved really choppy until about 3000 rpm. Would clear up and run great after that but I noticed that the timing mark on the balancer jumped probly 10 degrees every time that happened. I thought that the brown wire being disconnected stopped the timing from being changed except by rotating the distributor. Am I missing something here? Has anyone ever had an ICM partially fail and cause these issues? Thanks in advance.

The TBI distributors have a limp home advance curve to them. The base timing can only be set acurately at base idle. From memory they jump up from Zero at Idle to about 10° BTDC at 1,200 and about 20° @ 3,500. Some carbureted marine engines run the small cap HEI EST distributors in bypass mode without ECM control. Set the timing at 10-12 BTDC and the distributor module provides a timing curve internally.

 

[L31MaxExpress]

That being said I would check your fuel pressure to make sure it is not falling off under load.

 

[Schurkey]

The "Marine" 8-pin TBI modules have a built-in timing curve equivalent to "centrifugal advance" in that it's RPM based (not load-based like vacuum advance.)

I'm not sure that the passenger-car/truck modules have that timing curve. I'm wondering if the change in "timing" is due to worn-out distributor gear, or sloppy timing chain.

At any rate, verify fuel pressure and then connect a scan tool--find out what the computer is trying to tell you.

 

[L31MaxExpress]

The "Marine" 8-pin TBI modules have a built-in timing curve equivalent to "centrifugal advance" in that it's RPM based (not load-based like vacuum advance.)

I'm not sure that the passenger-car/truck modules have that timing curve. I'm wondering if the change in "timing" is due to worn-out distributor gear, or sloppy timing chain.

At any rate, verify fuel pressure and then connect a scan tool--find out what the computer is trying to tell you.

The truck ones have a 3 step curve where the marine ones have a linear curve.

 

[evilunclegrimace]

My 94 recently developed an issue with sluggish acceleration under load until about 3200 rpm on the tach. At that point it picks up and starts pulling like normal. I replaced my cap and rotor because they had some corrosion on the terminals. I also replaced the Tps thinking that it was bad. No change after that. I checked timing with the brown wire disconnected. It didnt want to run that way, revved really choppy until about 3000 rpm. Would clear up and run great after that but I noticed that the timing mark on the balancer jumped probly 10 degrees every time that happened. I thought that the brown wire being disconnected stopped the timing from being changed except by rotating the distributor. Am I missing something here? Has anyone ever had an ICM partially fail and cause these issues? Thanks in advance.

How old are the plugs and wires? It may be that you have misfiring cylinders. what does the top of the distributor look like? is the reluctor corroded?

 

[Lscobra]

Thanks for the replies. Inwent ahead and put new plug wires, new coil and ignition control module. I set the timing at 0 degrees (bottom of the largest valley on the tab). It still doesnt run right. The distributor is tight. Its throwing the electronic spark error code also, when the check engine light comes on. Still has inconsistent power through the rpm range.

 

[Lscobra]

How old are the plugs and wires? It may be that you have misfiring cylinders. what does the top of the distributor look like? is the reluctor corroded?

I do t see any corrosion, the wires were old but I replaced them today with no real improvement. Theres no play that i can find in the shaft. I havent removed the distributor yet though.

 

[texas tough]

first dont rev it up when setting base timing,,
check to be sure the coil wire is not arcing over to anything, put a tarp over the hood or at night run the motor and look for arcing.
set timing to ZERO or if the engine is tired, 1 degree BTDC..
Your problem is likely they little coil in the distributor is failing ,and or the magnets in the reluctor wheel are cracked, and the contacts on the reluctor wheel are rusty.
do yourself a favor.,,.dont waste your time and money.. get you a complete distributor from autozone, the duralast gold with lifetime warranty,. put it in and be done..