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Discussion Starter #1 (Edited)
Here is the deal. I have a 92 4.3 that was CPI converted to propane. I still have the distributor from the CPI set-up. Ive been feeling that my 4.3 doesnt seem to have the guts that it should have compared to other 4.3's and 4.0's. Ive always questioned the timing in the motor, seems to be the only think that I could have changed. Originally when I timed it I did it by ear, I didnt have a timing light so it was the best I could do. Now I put my light on it and it seemed to be way retarded. I couldnt even see the marks where it was firing. When I pulled it around to where it met the orignial marks it would not idle as low but seemed to rev a little better with no load, but it would pop alot. So now it fires with the mark just to the right of the tab at idle, it pulls right up to the center of the tab at around 1500rpms. At the moment it has no power at all, it doesnt have enough power to turn around in my driveway with welded diffs. What am I doing wrong, and what am I supposed to time it too?

Edit, I started messing with it when I finally got a tach and found my engine wouldnt really rev past 4k under no load.
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you pulled the timing connector when you timed it? single wire, tan i think? its under the factory glove box in the blazers...


?
 

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I set mine at 12 btdc on propane, but its an hei distributor on a tbi motor, but it's built a little. I bought an inductive light, so much easier.
 

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Discussion Starter #4 (Edited)
I dont have the larger plug into the distributor. My entire ignition system is Power wire to coil, I have one the high votage from coil to distributor and a red and a white wire from coil to distributor. Red seems to have 12v when key is on, the white is the tach signal. So there is no wires to pull when timing.

I have an inductive light, pretty handy. To find 12 BTDC did you find TDC on #1 and use a angle finder for 12 off that? Only way I can think of to do it.
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I dont have the larger plug into the distributor. My entire ignition system is Power wire to coil, I have one the high votage from coil to distributor and a red and a white wire from coil to distributor. Red seems to have 12v when key is on, the white is the tach signal. So there is no wires to pull when timing.

I have an inductive light, pretty handy. To find 12 BTDC did you find TDC on #1 and use a angle finder for 12 off that? Only way I can think of to do it.
:shaking:i didnt think before posting.


does yours have that plastic timing cover also? id guess thats the only way to check it...
 

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So you have nothing to advance the timing correctly? IIRC CPI used a standard 7/8 pin EST that gives no advance till 2500, then it adds like 10 degrees. Limp home they call it. Lousy way to actually run the motor unless there is something about propane I don't know. It would seem to me that an HEI dizzy with vac and centrifugal advance would be a MUCH better setup if you don't want to use the gm ECU's timing curves by hooking up map signal, tps, and speed.

Is your 4.3 skip fire or even?
 

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If you are referring to 6al's and such, no. I don't believe they have any spark advance curve. What do you mean it advances spark consistently? IIRC they immediately jump 10 degrees at one point.
Regardless, not having a vacuum advance seems like you wouldn't be able to utilize that motor anywhere near it's potential.

I honestly think you should find a vacuum and centrifugal advance dizzy for a 4.3.

There were two different kinds of 4.3's, ones that fired every 120 degrees, and ones that fired every 90 and skip two cycles. Since all 4.3's are 90 degree blocks like their 350 cousins, the 120 degree fire engines had to have 30 degree offset ground main journals so they fired evenly.

The skip fires used a cheaper to make non offset ground crank that looks like a cut off 350 crank and then a special dizzy that has un evenly spaced plug wire points. I think these were a bit rare to find with a dizzy. Most use DIS so that the computer takes care of the offset.

one other thing, spark should advance smoothly from base at idle all the way to 3500 smoothly and without jerks. Then based on load, sensed by vacuum, advance as there is less load/throttle position.
 

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Discussion Starter #9 (Edited)
If you are referring to 6al's and such, no. I don't believe they have any spark advance curve. What do you mean it advances spark consistently? IIRC they immediately jump 10 degrees at one point.
Regardless, not having a vacuum advance seems like you wouldn't be able to utilize that motor anywhere near it's potential.

I honestly think you should find a vacuum and centrifugal advance dizzy for a 4.3.

There were two different kinds of 4.3's, ones that fired every 120 degrees, and ones that fired every 90 and skip two cycles. Since all 4.3's are 90 degree blocks like their 350 cousins, the 120 degree fire engines had to have 30 degree offset ground main journals so they fired evenly.

The skip fires used a cheaper to make non offset ground crank that looks like a cut off 350 crank and then a special dizzy that has un evenly spaced plug wire points. I think these were a bit rare to find with a dizzy. Most use DIS so that the computer takes care of the offset.

one other thing, spark should advance smoothly from base at idle all the way to 3500 smoothly and without jerks. Then based on load, sensed by vacuum, advance as there is less load/throttle position.
Ok, I guess I will break down and get a different distributor. By consistently I meant that it advnaced at the same RPM every time, but the total advance would happen in about 300 rpms. My 4.3 had a distributor on it before as it was a 92 so it would be a 120 degree engine.
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$75 from the local yard here. This shit sucks. I guess a 6cyl cap will not fit on the 8cyl dizzy will it? A brand new v-8 one is less than a 23 year old one from the JY.
That's why I was wondering if it was skip fire as I think there is a way to use a v8 one.

What application are you looking for?

You might be able to put the v6 reluctor and pickup coil from small cap dizzy that you have, into the v8 hei dizzy with vacuum and centrifugal advance. Then use a cap for a 1985 c10 with 4.3. This should match right up. I've got a few of both laying around, i'll look at this tomorrow.

The entire distributor out of a 1985-86 4.3 truck I think is the only one that will work for you. And only certain ones. Some were already using computer controlled ignition and had an entire TBI style ecu under the dash even though they were running a q-jet, and consequently no advance built into the dizzy. Here is the cardon part you need. 301685

under a hundered new on rock auto, shows picture of what it should look like there too if this doesn't work



Of course what you should be doing is using and tuning the stock gm ecm so you have complete control over your spark curve, like us cool EFI kids doo. :grinpimp:
 

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Discussion Starter #13 (Edited)
Update, Ive been out of town so I couldnt mess with it but the new dizzy should be at Advance for me to pick up as soon as I get out of class. I went to a JY with the 85 c10 application and each one there had 2 plugs in them with a vac pod on them. I think these were the q-jet/ecm controlled ones you mentioned.

Anyways, when I go to time it, what rpm should I be doing that at?

I was not able to find out in the v-6 cap would fit on the v-8 dizzy. visually it looked like it would work but no one would let me try a test fit. My tach has a 4,6,8 cylinder option so I think I would just have to set my tach to the 8 cylinder option for it to work correctly if I am thinking right.
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