He everyone. Got a stumper here. My car is a 1985 Z28, manual trans, 305 carbureted.

I understand that these cars are supposed to have electronic feedback carburetors on them, but my feedback carb came in a box in the back seat. someone had replaced it with an earlier model qjet. the car runs okay with this carb on it, but i would prefer the correct one.

I have tried re-installing the feedback carb, and the car will star and idle with no problems whatsoever. the engine is also very responsive while the car is in neutral, but it refuses to leave the garage. any attempt at moving results in a violent surging, if i can keep the engine running. im assuming the carburetor is not metering right, but i have no idea what i am looking at here.

 

I am making the assumption you have checked all vacuum lines.

Have you confirmed that the timing and idle speed is set correctly?

Is it throwing any codes?

Choke working correctly?

Surging in gear makes me think it's a vacuum issue, if it isn't that I would recommend a rebuilt carb.

I took the easy route and bought a rebuilt carb off ebay from this guy

Mountain Man Fuel Systems

Good price and good carb.

 

There's probably a reason it was in the box. Time to open it up and rebuild it, pretty easy job altogether. If you decide to go that direction let us know and I can point you towards some walk thrus.

 

well, i honestly didnt know the car was capable of producing trouble codes. my SES light must be burnt out then, because running like it does should throw one somewhere. it should be OBD I, correct? or possibly something earlier?

yes to both the choke and vacuum lines. made sure no lines where cracked, and the choke is swapped between carbs. seems to open kinda quick, but it opens. lol

I think im going to try a rebuild. a friend of mine suggested a problem with the "fuel control solenoid"? said he couldnt hear any clicking while it was running.

 

It should click with the key in 'run' and engine not yet started. Will continue to click for about 30 seconds or so before the ECM shuts it down if the car is not started. For some rebuild help try:

https://www.thirdgen.org/forums/carb...-ccc-qjet.html

Check for throttle bushing wear while you're there. You can hold open the throttle slightly and try to wiggle the primary throttle shaft back and forth. Should feel almost no perceptible movement. I'm seeing a lot more of these older carbs with wore out throttle shafts. They can be easily bushed to fix though.

and come back here with any questions.

 

You also mentioned that you have no SES light? When you first turn on the key before you start it, the check engine light should be on. If it isn't then you have a ECM problem, first thing I would check is to make sure it's there and has power. You're going to need to fix this problem before you move on to troubleshooting any other issues.

 

most likely the bulb has been removed by the previous owner who got tired of looking at it

second most likely is it burned out

if the MCS is not clicking at all, check your engine controls fuse first. this circuit provides power to all of the things the ecm controls. ecm power is through a fusible link, directly from the battery running along the right fenderwell.

 

I agree
Yes OBD I and the codes are the same as anything else OBD I

A few things to check before you go too far with your car.

• It's always good to check the fuses
• Check the distributor to make sure you still have the ECM controlled distributor. 4 wires coming out to the ECM harness. They could have swapped this too.
• If you have an ohm meter, measure across the top pin and center pin of the TPS and see if the resistance changes smoothly with the throttle movement. After that go from the center pin to the bottom pin and the resistance should change in reverse of the first test.
• If you are going to rebuild it check this article out... http://www.carcraft.com/techarticles...d/viewall.html
  

 

yup, someone took out the bulb for the SES light. lol

so, just for ***** and giggles, i took the cc carb back out today and swapped it onto the engine. i get one click when i turn on the key, nothing more. found a spot where i can fit a small screwdriver in on top of the plunger and can see it is only snapping shut. dosent change when i start the car either. only returns when i shut it off. since i was experimenting though, i unplugged the mixture solenoid while the car was running and got some interesting results. i know i said earlier that the engine runs fine with this carb on it, but unplugging the mcs made it idle even better. also, the car became drivable! it actually runs really well! i took it down the street for a bit and was rather impressed. can tell its very rich though. swapped it back to the other carb though and have the cc back on my bench. took a quick look at the shafts and did find play in the primary. should be able to find bushings at car quest or something, right?

thanks for all your help guys! im really exited about getting this car right again. its been neglected for so long.

 

If the mixture control solenoid is staying closed once started and never moving, then the solenoid is bad or there is an issue with the ECM telling it to stay pulled in. If you're rebuilding the carb, make sure to replace the solenoid. The fact that it only clicks once when you turn to key to on leads me to believe that this may be the issue. If the problem stays the same, then there is an issue with the ECM which may also need replaced.

 

check your ecm by trying to get it to flash the 12 code

you can get a bushing kit from carbs unlimited or one of the other internet sources.

it idled better with the mcs unplugged because it was running full rich

 

Okay, thanks guys. ill look into getting a new solenoid too. What is the 12 code though, and how do i make it flash? self diag code or something?

 

https://www.thirdgen.org/service-eng...ht-error-codes

Don't buy a new MCS yet.

 

sorry guys, been pretty busy lately. finally got around to trying to flash the codes though and ran into another problem. ive only got a 4 pin connector. its a 12 pin socket, but only 3-6 have electrical pins in them. WTF!?

 

Ya who knows what GM was thinking, maybe going to add pins later? instead they went to a whole different system :P

You only need to short pin A and B with key on and read the blinking codes on check engine light. If you have a shop manual it will explain this.

 

Okay, from what i gather, a and b are the two on the far right. i tried connecting the two and got absolutely no response. just a steady SES light.

 

wait, i just remembered. The previous owner had attempted to wire their own stereo into the car and damaged a lot of the wiring. (melted it all together actually. im suprised the car didnt go up in flames.) Perhaps the ALDL terminal wiring got messed up in this too. Ill look into this, then get back with results.

 

short the top right pins, A and B with ignition in 'run' or engine running.

 

okay, now im very confused. naf, i tried like you said and still got no response. i checked over the wiring and somewhere through the mess unhooked the ECM and forgot to reconnect it. I didnt realize this because when i turn the key on, the SES light still comes on and the car will actually start and run like it always does. now, i understand that if im using a different carb, that takes away almost 3/4 of the computers work, but shouldnt the distributor still be controlled by it? This is my first carbureted car, but anything i have worked on (cars, motorcycles, 4-wheelers) even the simplest of systems wont run without their computers.

oh well, anyway, i guess that if removing the ECM creates no difference in the way the vehicle operates would lead me to believe that it was never working to begin with, so i guess one could say the problem has been located. lol not the results i was hoping for.

 

btw, i amend my previous rant. that was in reference to any system having a computer to control anything. lol im still baffled though.

 

Which is why when I first post I told you to check and make sure the ECM was there and connected correctly.

On newer vehicles if the ECM is bad it own't run because of injectors and a lot of things that are controlled by it. On these older cars only a couple of things are controlled with the ECM. The vehicles will still run without the ECM or if the ECM is having issues they just won't run optimally since the ECM controls very important things for mileage, driveability and Emissions. Without the ECM you will only be able to run base timing, the ECM advances it according to eninge RPM using the MAP sensor and TPS(which is one of the sensor on the carb). It also controls converter lockup along with various other emissions devices. All the basic functions needed for a E4EC carb to function are there without ECM input, new cars they are not.

 

With the ECM disconnected the carb will be running full rich and you'll get some throttle transition issues and terrible mileage. The control module in the dist contains a weak timing curve that will allow it to 'limp' home without the ECM's input.

 

I haven't heard what type of distributor it has. The factory distributor is electronic only, no vacuum or mechanical advance. It doesn't work well with a non-computer carburetor. Likewise a non-computer carb should have a non-computer distributor, and if the non-computer carb switch was done properly, that's what the car has on it.

So, a computer carb would not work well unless it also has a computer distributor. The computer needs information from both before it can give the proper commands to either.

 

yeah, i know, and at that time it was. im the one who unhooked it. lol


No, the transition was not done properly. it still has the computer controlled distributor on it. so, i guess this all boils down to two new questions.

a. who has a vacuum advance HEI they would like to sell?

b. anyone want a ccc q-jet once its rebuilt?

 

BTW: I really appreciate all the help you guys gave trying to figure this out. Didnt end up with the results i was hoping for, but my guessing game is now over. thanks again everyone!