[Elcaminojt]

As some of you may have read before, I am trying to work the bugs out of my 83 El Camino's engine. I have a late '86 Corvette 350 with aluminum cylinder heads with my factory computer feedback carburetor system installed. I am running stock 83 aluminum intake, a High Energy Comp Cam(p/n 12-210-2), and no emissions equipment(smog, EFE, EGR, Catalytic Convert). It has a tendency to stumble/misfire a bit on light acceleration(between 1,000 and 1,800 rpm), and stumble at higher RPMs (4,500-5,500) at wide open throttle. I am sure the higher rpm problem is the secondaries are opening to soon because I haven't adjusted them yet, but right now I am focusing on the low rpm stumble for everyday driving. I was wondering if the timing would be a problem because of the different cam setup and the stock computer chip. I was told by someone to go beyond doing basic ignition timing and do total ignition advance timing. I have read on how to do that with non-computer engines, setting total advance between 32 to 36 degrees of total advance. However, everything says to unplug the vacuum advance and plug the hose, set the base timing, then take it up to about 3,000 rpm and dial the timing in off of the mechanical advance. Can this be done to a computer controlled distributor? I can set the base timing no problem, but when I have done this in the past I had to play with the throttle to get the engine to stay running. I remember looking at the timing mark when I snapped the throttle and not seeing the timing move. There are no mechanical weights or springs under the rotor button, so it looks like all of the ignition advance is controlled by the computer. Since this appears to be the case, does it stand to reason that to adjust total ignition advance I should leave the distributor plugged in and rev the engine to 3,000 rpm to adjust the total advance? Also, if anyone has any other ideas about how to get rid of this low rpm stumble, I would appreciate it because the way my rear end is currently geared with my overdrive transmission, my truck runs at really low engine speeds to the point that I have to drive around town in 2nd gear to keep the engine speed above 1,800 just for smooth operation. I actually don't shift into 3rd until 55mph just to keep the engine speed above that point and I don't even use 4th anymore.

 

[xcookpac]

Only if you keep the distributor plugged into the computer harness will you be able to measure total advance. Be sure to also note at what rpm you get to total advance.

 

[464elky]

I am going to speculate that your stumble is too lean a mixture. With the chip you have in the ecm I don't think that is going to work. Messing with the timing on your setup is not really going to help in that the ecm just adjusts it to where it wants it based on the feedback from the sensors. More cubic inches, more cam, different flowing heads = ecm programming is confused.

 

[rnhart3]

Why not dump the CCC carb for a regular Quadrajet and add a mechanical distributor?

 

[gilby]

Why not dump the CCC carb for a regular Quadrajet and add a mechanical distributor?

..X2..:beer:

 

[Elcaminojt]

I am going to speculate that your stumble is too lean a mixture. With the chip you have in the ecm I don't think that is going to work. Messing with the timing on your setup is not really going to help in that the ecm just adjusts it to where it wants it based on the feedback from the sensors. More cubic inches, more cam, different flowing heads = ecm programming is confused.

I thought that the ecm was only able to maintain the fuel mixture around 14.7:1. Shouldn't I be able to eliminate that problem through carburetor adjustments? I have tried to change the mixture screw adjustments seeings how at low rpms the mixture circuit in the carburetor still play a significant roll and have not seen any change. I have turned those screws from 2 turns out to 4 turns out and no real change in performance. I have been told before that a regular E4ME Quadrajet off of a 305 would still work on a 350, just some settings would need to be tweeked. The carburetor was purchased as a re-man from a parts store and I had a master tech who used to work for G.M. in the '80s rebuild it to fix the re-manufacturers mistakes. That really helped because United Carb did a terrible job with it but this problem still remained. So I though timing might be the issue.

 

[Elcaminojt]

Why not dump the CCC carb for a regular Quadrajet and add a mechanical distributor?

Well, in an attempt to get better gas mileage I re-installed the CCC system to help which it has a little bit. When the stock 305 was in it with a TH350 trans and 3.73:1 rear gear ratio I was getting 22 to 24 mpg highway. I am well aware that I am not going get as good of numbers as when I had the stock engine and that ratio in it but I figured that I would see some improvement. With the Comp Cam installed in the 350, TH700R4 trans, and 2.41:1 gear ratio now(unfortunately), I was expecting to get in the neighborhood of 16 to 18 miles per gallon highway, but I believe I am still running around 11 to 14. Now this might be do to the low gearing in the rear end that I mentioned before but I figure once the engine starts running smoother, I should see some better results.

 

[Guest]

Well, in an attempt to get better gas mileage I re-installed the CCC system to help which it has a little bit. When the stock 305 was in it with a TH350 trans and 3.73:1 rear gear ratio I was getting 22 to 24 mpg highway. I am well aware that I am not going get as good of numbers as when I had the stock engine and that ratio in it but I figured that I would see some improvement. With the Comp Cam installed in the 350, TH700R4 trans, and 2.41:1 gear ratio now(unfortunately), I was expecting to get in the neighborhood of 16 to 18 miles per gallon highway, but I believe I am still running around 11 to 14. Now this might be do to the low gearing in the rear end that I mentioned before but I figure once the engine starts running smoother, I should see some better results.

The gears you have are numerically low but we call those high gears since those are used for the highway in most cases. A low gear would be a numerically high number such as 4.11's,4.56's and so on. Those types of gears are more for the track and are terrible for daily driving.
Your problem seems to revolve around the carb and distributor you have with an aftermarket 350. The 350 is certainly throwing the computer off and giving the wrong readings to adjust to the engine,which in turn is giving you bad mileage and performance.
Timing will not help in this case since the engine has the stock stuff reading it.

 

[61Airstream]

As some of you may have read before, I am trying to work the bugs out of my 83 El Camino's engine. I have a late '86 Corvette 350 with aluminum cylinder heads with my factory computer feedback carburetor system installed. I am running stock 83 aluminum intake, a High Energy Comp Cam(p/n 12-210-2), and no emissions equipment(smog, EFE, EGR, Catalytic Convert). It has a tendency to stumble/misfire a bit on light acceleration(between 1,000 and 1,800 rpm), and stumble at higher RPMs (4,500-5,500) at wide open throttle. I am sure the higher rpm problem is the secondaries are opening to soon because I haven't adjusted them yet, but right now I am focusing on the low rpm stumble for everyday driving. I was wondering if the timing would be a problem because of the different cam setup and the stock computer chip. I was told by someone to go beyond doing basic ignition timing and do total ignition advance timing. I have read on how to do that with non-computer engines, setting total advance between 32 to 36 degrees of total advance. However, everything says to unplug the vacuum advance and plug the hose, set the base timing, then take it up to about 3,000 rpm and dial the timing in off of the mechanical advance. Can this be done to a computer controlled distributor? I can set the base timing no problem, but when I have done this in the past I had to play with the throttle to get the engine to stay running. I remember looking at the timing mark when I snapped the throttle and not seeing the timing move. There are no mechanical weights or springs under the rotor button, so it looks like all of the ignition advance is controlled by the computer. Since this appears to be the case, does it stand to reason that to adjust total ignition advance I should leave the distributor plugged in and rev the engine to 3,000 rpm to adjust the total advance? Also, if anyone has any other ideas about how to get rid of this low rpm stumble, I would appreciate it because the way my rear end is currently geared with my overdrive transmission, my truck runs at really low engine speeds to the point that I have to drive around town in 2nd gear to keep the engine speed above 1,800 just for smooth operation. I actually don't shift into 3rd until 55mph just to keep the engine speed above that point and I don't even use 4th anymore.

I think I am having the exact same problem with my new 350/290 crate motor. I talked to three people yesterday that used to burn custom prom, but don't do now because they can't get the blanks. They have been discontinued. The guy at Motorvation said he would burn one for about $150 if I supplied the blank. He said he mainly works with the spark curve and doesn't do much to fuel delivery. Both he and one other fellow said I could probably increase the timing a couple of degrees and over come the problems with the ECM. He said if I advance it too high I will start to get ping.

Jim

 

[JJLT1]

I remember looking at the timing mark when I snapped the throttle and not seeing the timing move.

so it stays at initial timing??
are you saying the timing never changes?? if the timing dosnt move?? the advance is not working..

 

[Elcaminojt]

so it stays at initial timing??
are you saying the timing never changes?? if the timing dosnt move?? the advance is not working..

What I mean is when I am setting the initial timing with the distributor unplugged from the computer and increase the engine speed the timing stays the same. When I plug the distributor back in and start the vehicle the timing moves when the rpm increases. What I was trying to describe before was how there was no mechanical springs or weights under the rotor button like in a traditional HEI distributor and that the computer is fully controlling the ignition advance.

 

[darbysan]

Is the computer giving you any codes? With no EGR, I would assume you are at least getting code 32. Problem does sound like fuel flow. If you are getting misfires at lower RPM's, but not under acceleration, then it eliminates the Accelerator Pump and the Secondaries. When you adjusted the carb, did you use a Dwell Meter hooked to the Green single connector on the front of the carb? Is your O2 sensor working properly? Sounds like maybe the Rich Stop is too lean for your setup. The ECM can try to open the primary rods, but it they are restricted, you will be lean.

 

[Elcaminojt]

Well yes I do regularly have codes that pop up but only a few times with code 32. For my set up it was a MAP sensor that was broken and after I replaced it hasn't come back. The codes that are consistent are 13,23(when I unplug the M/C solenoid), 24(broken speedometer), 41(when I'm playing with the timing) and 44. As far as the misfires and stumbling I do get them under light acceleration as well as consistent driving between 1,000-1,800 RPMs. For the Carburetor electronic adjustments, the rich stop and lean stop were set by a master tech. when he rebuilt it for me. He has all of the books from his time at G.M. in the '80s for the rebuild. I assume he has them correctly set but it is possible that being a bigger engine it might need to be re-calibrated accordingly. I'll run that by him and see what he thinks. As for the O2 sensor, it is a brand new A/C Delco factory sensor. However I have had to relocate it due to the long tube headers not having a place for it. It is a little further down the exhaust pipe about 6-8 inches behind the collector. I have been told that it will take longer for the sensor to reach the proper operating temperature but once it does it should still work okay. The only thing that was advised about was the possibility that being that far down the pipe instead of in a cast iron manifold I might need to attach a ground strap to it. I haven't done that yet but I am going to check that soon.

 

[Jack_K]

I think I am having the exact same problem with my new 350/290 crate motor. I talked to three people yesterday that used to burn custom prom, but don't do now because they can't get the blanks. They have been discontinued. The guy at Motorvation said he would burn one for about $150 if I supplied the blank. He said he mainly works with the spark curve and doesn't do much to fuel delivery. Both he and one other fellow said I could probably increase the timing a couple of degrees and over come the problems with the ECM. He said if I advance it too high I will start to get ping.

Jim

I can program the EPROMS if you supply the information.

Jack

 

[darbysan]

JT, the O2 being down the pipe could be part of the issue. It takes a while for it to heat up, and usually in the lower RPM range it just doesn't get enough heat to work. You can tell by measuring the output with a DVM. If it is a steady voltage, then it is not working. If you are getting .3 to .7 volts, fluctuating back and forth many times per second, then it is working. The higher the voltage, the richer the condition it is seeing ( and therefore telling the ECM to lean out the mixture). Most of us with headers use a heated O2 sensor to resolve this issue. If the ECM is not seeing the voltage fluctuate, then it reverts to a base setting (basically a guess as to how rich/lean the carb is running), which would not be accurate for the 350 with cam and headers.

I don't have my manual with me regarding the codes you were getting, but others should chime in.

As for setting the carb, it sounds like it was adjusted off the car? If this is the case, it definitely needs to be fine tuned on the vehicle with the dwell meter, in closed loop with the O2 sensor working properly. There is no way to do the final settings without the car running in closed loop mode, and it makes a big difference in how the carb will perform.

 

[Elcaminojt]

Thanks for the tip on the O2 sensor. I wired in a 3 wire sensor from a 92 C1500 5.7L and cleared the codes out of the memory. Now a new code popped up that I hadn't seen yet. Code 45, Rich Exhaust indicated. So now I am trying to adjust the carburetor according to my shop service manual and have not seen any results. It says to set the idle mixture screws to 3 3/8 turns out and leave them alone. Then to adjust the idle bleed screw at the top of the choke tower while watching the dwell meter connected to the mixture solenoid test lead in 6 cyl. scale. The book says to adjust the idle bleed screw while the truck is idling in drive to try to reach 25-30 degrees of dwell and to only turn it in 1/8 intervals. I turned it both clockwise and counterclockwise two full turns and the dwell did not budge from 50 degrees. Do you have any ideas on what needs to be done now?

 

[hotrodelco]

Can you hear the M/C solenoid clicking, if not, its not working.:texas:

 

[darbysan]

X2- sounds like The MC Solenoid. Or, it could be that you are still stuck in closed loop. You can check for continuity of the MCSS by Ohming it with a DVOM.

 

[hotrodelco]

X2- sounds like The MC Solenoid. Or, it could be that you are still stuck in closed loop. You can check for continuity of the MCSS by Ohming it with a DVOM.

"could be stuck in open loop, not closed loop"
You really need to find someone with an old scanner that reads these old CCC systems. :texas:

 

[Elcaminojt]

Well, the mixture solenoid is clicking on start up so I know it works. I'm pretty sure that its going to closed loop mode because I am getting the check engine light with code 45. If it wasn't in closed loop, I do not think it would give trouble codes. Also the car changes how it behaves after driving for 10-20 minutes. At idle though 1,600 rpm the light will come on after that much run time. When I get on the freeway the engine light goes out until I get off and back into town. I have a craftsman scan tool that is supposed to work on OBD1 and OBD2 systems but it doesn't seem to work when I plug it in to the ALDL connector. Any ideas why my ALDL connector may not be working? The computer is seems to be working and I am able to receive flash codes when jumping with a paper clip.