Q-Jet problem

[ellero]

I have an 84 K5 with a 350 motor.
I did a conversion from a 700R4 / 208 to a T-350 / 203 (w/ part time kit).

I lost my cruise control after that and its running rich. Sometimes it runs great and sometimes its like its only running on 4 cyl. with black smoke pouring out the tail and not enough power to back up the driveway.

I assume that I lost my cruise control and its running rich because the computer speed sensors that are on the 700R4 are not on the T-350 so they are not pluged in to anything. Am I correct in this guess?

My thoughts are that I will have to go with an older NON computer controlled Q-jet to fix this problem. If that is true, what years of NON computer controlled q-jets will fit the 84 intake manifold and still connect with the kick down cable on the 78 T-350?

If the NON computer controlled Q-jet is used, what other parts will I need to change out to have the motor run smooth and reliable again? Once again its an 84 K5 with a 78 T-350 tranny.

Please help,

John

 

[dyeager535]

You might just want to double check your wiring, fuses, etc. From what I know of the truck CCC system, from what you say you did, there should be no reason that it doesn't work fine, unless you cut some wires or removed something like the O2 sensor. There are no speed sensors in the transmission or t-case until 1990, so that isn't the problem. The only speed input the ECM and cruise need come from the back of the speedometer. As long as that's hooked up, your ECM is getting what it needs.

I'd see if you can't figure that out first, and forget about swapping carbs. I was under the impression that the 700 and 350 used the same TV/kickdown linkage attachment at the carb end.

 

[ellero]

You might just want to double check your wiring, fuses, etc. From what I know of the truck CCC system, from what you say you did, there should be no reason that it doesn't work fine, unless you cut some wires or removed something like the O2 sensor. There are no speed sensors in the transmission or t-case until 1990, so that isn't the problem. The only speed input the ECM and cruise need come from the back of the speedometer. As long as that's hooked up, your ECM is getting what it needs.

I'd see if you can't figure that out first, and forget about swapping carbs. I was under the impression that the 700 and 350 used the same TV/kickdown linkage attachment at the carb end.

I did too before the swap, but the kick down cable on the 700R4 is actually a speed sensor of sorts and is electronic. The 700R4 has to electronic sensors on it that the T-350 doesnt. The T-350 is a manual kick down. Thats why I thought it had something to do with it. Now my Spedo cable failed so if the cruise is based off the spedo, that would make sense too. Thanks for your input.

 

[dyeager535]

You are not quite correct, unless you had a 4L60E swapped in, which I guarantee you didn't. The only thing electronic on most, if not all, 700R4's is the TCC, and that has nothing to do with the TV cable, although there might have been some sort of spark control stuff on the early 700's I'm unaware of, and that would be a plug seperate of the drivers side TCC connector.

The TCC on your truck was PROBABLY handled by a vacuum switch, you'd need to look at a wiring diagram for your year, or at least find the vaccum switch(es) on your firewall, and trace the wiring. If it's handled by vacuum, then there is no interface between the ECM and the trans.

So as an edit, fix the speedo cable, see if everything goes back to normal. It should.

 

[ellero]

You are not quite correct, unless you had a 4L60E swapped in, which I guarantee you didn't. The only thing electronic on most, if not all, 700R4's is the TCC, and that has nothing to do with the TV cable, although there might have been some sort of spark control stuff on the early 700's I'm unaware of, and that would be a plug seperate of the drivers side TCC connector.

The TCC on your truck was PROBABLY handled by a vacuum switch, you'd need to look at a wiring diagram for your year, or at least find the vaccum switch(es) on your firewall, and trace the wiring. If it's handled by vacuum, then there is no interface between the ECM and the trans.

So as an edit, fix the speedo cable, see if everything goes back to normal. It should.

I wish I could say I knew more about it but I dont. I did have an issue after the swap where the check engine light would come on. The Smog tech said that the 700R4 has a 2 stage speed sensor on it and after the truck broke 25 mph twice, it would through a transmission fault code because it was not hooked up now that the t-350 was in. This was originally a California truck and CA uses tranny codes in their emisions testing. That is the other reason that I figured it was due to a tranny sensor. I never had the 4L60E trany

I moved to GA, and they dont care nor do they even want an inspection, so my only real goal now is to get it running good again.

 

[dyeager535]

So was the speedometer issue existent when you had the check engine light come on?

If you are going to fix the speedometer cable anyway, just do that, and see what happens. If that doesn't fix it, then you can decide if you want to replace the carburetor. Nothing inherently wrong with the CCC setup, it's as close to TBI as you can get, and still flow 750-800CFM, although the TPS on them seems to be a bit problematic.

 

[ellero]

So was the speedometer issue existent when you had the check engine light come on?

If you are going to fix the speedometer cable anyway, just do that, and see what happens. If that doesn't fix it, then you can decide if you want to replace the carburetor. Nothing inherently wrong with the CCC setup, it's as close to TBI as you can get, and still flow 750-800CFM, although the TPS on them seems to be a bit problematic.

The spedo has been out for quite a while and I didnt have the ruff running and super rich mixture before the swap. I just had a thought...I wonder if the distributor might have bumped the firewall and moved at all when raising and lowering the crosmembers to R&R the tranny? If that happened or any damage came to the cap and rotor, could that cause the intermintant 4 to 8 cyl operation? It is not always a problem, but does happen a lot without and special cause, tempature, or weather.

 

[dyeager535]

It could, you may have actually damaged the cap and/or rotor depending on how much contact it made. Vacuum hoses and all that need to be correct too, anything like that could throw off the MAP sensor, and there were enough ported/switched vacuum lines on those motors.

 

[ellero]

It could, you may have actually damaged the cap and/or rotor depending on how much contact it made. Vacuum hoses and all that need to be correct too, anything like that could throw off the MAP sensor, and there were enough ported/switched vacuum lines on those motors.

That was one of the other reasons I considered getting rid of all of the CCC system and go back to basics of a carb, motor, and exhaust so that I didnt have to worry about it and cut out all the extra emmisions and extra vacuum lines and crap. I just want it to run well and be able to troubleshoot it easier when something is not right. Just dont know if going back to the basics will better or worsen the performance and reliability at all.