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CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
I recently had my quadrajet E4ME rebuilt professionally. Also certified working on their dyno. Once installed it ran but my rough idle issues and gray smoke issues continued. Here's what I've done:
TPS adjustment and needle/seat/float were replaced and set by the reubilder.
Front idle mixture screws were ground and cut by the rebuilder so I could adjust with a flat blade instead of the special tool. Both are set to 3.5 turns out from seated.
The idle air bleed screw is 4 full turns out from fully seated.
Electric choke is working properly and there is a new vacuum break installed. Linkage is not bound and I can watch the butterfly plate open and close.
New PCV valve, vacuum lines. Spent hours making sure there were no other vac leaks - almost all vac line has been replaced. dont see any leaks around the base of the carb.
I went back to check timing and have an interesting issue:
WITH THE AIR CLEANER HOUSING ATTACHED:
I set base timing by removing the 4 wire timing advance connector on the back of the distributor and set timing to 6 degrees. It idled very high but smoothed out and I was able to set timing. It smoked like crazy.
Once I plugged the distributor connector back in it runs very low idle and rough, eventually diesels a bit and dies.
WITH THE AIR CLEANER HOUSING REMOVED: it will idle rough but at least stay running. As soon as I plug the air cleaner back in it will choke and die. Attached is a picture the port circled in red - it routes to the bottom of the air cleaner assembly to a small nipple with a hole in it. I cleaned that up a bit to make sure it wasnt clogged.
I get a very rich gas smell, gray but not black smoke out of the tailpipes and breather.
To recap - timing seems good without the advance, once advance is introduced it idles poorly and will eventually die. Removing the air cleaner assembly helps but is not great.
Is my timing good but I'm running extremely rich and the open carb port is leaning it out? Any help is appreciated. Thanks.
I went through similar problems last year on mine that were primarily caused by the outer ring on the harmonic balancer slipping. Try putting the timing where the engine likes and see if anything changes.
I went through similar problems last year on mine that were primarily caused by the outer ring on the harmonic balancer slipping. Try putting the timing where the engine likes and see if anything changes.
Interesting. So your timing mark wasnt accurate? I didnt know there was such a thing.
Did you time yours with the air cleaner and advance plugged in?
you should plug that port when the air cleaner is off.
the ecm should set the idle bump stop when it sees that the distributor is disconnected, and it should idle at around 600-800 if warm.
if you set the base timing with the engine rpm too high (plug removed) you'll be setting it AFTER the ICM has added its limp home advance step. the ICM has a built in advance that kicks in somewhere above 1000-1200 rpm. you can observe this step increase with a timing light if you rev the motor with four-wire connector unplugged.
looks like you have an 87? you may consider setting the timing for best idle and lack of pinging with the KS disconnected.
you will almost certainly require some adjustment of the IAB for proper dwell at some point as well.
Plugging the port has no effect on setting the ignition timing.
(Note that I am not saying "don't plug the port", "leave the port unplugged", "leaving the port unplugged doesn't matter", or ANYTHING ELSE OF THE KIND; only, that it has no effect whatsoever on the results while setting the ignition timing)
The ECM should command about 20° of add'l advance over whatever you set the static to, when you plug the connector back in. Since the ECM has NOT THE FAINTEST FOGGIEST DIMMEST REMOTEST HINT OF A WHIFF OF A GLIMPSE OF A CLUE what the timing actually IS, then all it can do is, look up in its little table of programming, what OFFSET to apply to the pulse it receives from the dist, and apply that OFFSET to the spark. The ONLY way it has of knowing ANYTHING about when the spark ACTUALLY occurs is the knock sensor; and even then, all it knows is "too soon". Doesn't know how much too soon, how much too late any other time, etc. It's really quite dumb.
I would add also that the throttle stop solenoid doesn't have enough nads to overcome the throttle return springs on its own unless the springs have been altered. (more specifically, in factory condition, it is deliberately designed NOT to be able to do that) All it can do is HOLD the throttle open once the solenoid has ALREADY OPERATED. I.e., apply power to it, open the throttle a bit, the solenoid will then be able to pop out (the "operate" and "hold" power of a solenoid are VERY different), let the throttle close against it, and it will hold it up. Won't be able to crack it open on its own though.
when setting initial timing the idle rpm must be low enough so that the ICM has not added in its 'limp home' timing advance step increase. this step occurs somewhere above 1000 rpm but is in by 1500 rpm, if I recall correctly. not an issue in most circumstances.
leaving the port unplugged will add to idle speed, agree that it should not add enough for this to be an issue...but combined with a carb out of adjustment, best to be aware of this behavior. if base timing was set at too high an idle it may have been inadvertently set too low.
My experience is that the act of starting the motor tends to lift the throttle off of the curb idle stop enough so that it can rest on the idle bump solenoid, especially when starting it with EST disconnected.
when setting initial timing the idle rpm must be low enough so that the ICM has not added in its 'limp home' timing advance step increase. this step occurs somewhere above 1000 rpm but is in by 1500 rpm, if I recall correctly. not an issue in most circumstances.
leaving the port unplugged will add to idle speed, agree that it should not add enough for this to be an issue...but combined with a carb out of adjustment, best to be aware of this behavior. if base timing was set at too high an idle it may have been inadvertently set too low.
My experience is that the act of starting the motor tends to lift the throttle off of the curb idle stop enough so that it can rest on the idle bump solenoid, especially when starting it with EST disconnected.
Ok this makes a lot of sense - I was unaware of the limp setting by the ICM. I will remove air cleaner, plug that port, remove KS and set base timing from there
no need to plug the port or remove the KS. just ensure it is idling below 1000 rpm when setting base timing.
there is also the real possibility that your timing marks are off, as mentioned above. in that case you can set base timing without the light for good idle (with everything connected) then increase it in increments until you don't have any pinging with throttle tip in at low speed cruise. disconnecting the KS keeps the ECM from pulling the timing back with knock and will make it easier to perceive the slight pinging that will indicate that the timing is too advanced. if it pings, decrease the timing incrementally until it doesn't.
with mine I've incrementally bumped the base timing up a few degrees then run a tank or two through checking mileage. at some point, when it's too advanced, mileage will drop as a response to the ECM/KS pulling timing due to knock. I have a fairly rigid commute to work and back that takes many of the variables out of my mileage checks though.
no need to plug the port or remove the KS. just ensure it is idling below 1000 rpm when setting base timing.
there is also the real possibility that your timing marks are off, as mentioned above. in that case you can set base timing without the light for good idle (with everything connected) then increase it in increments until you don't have any pinging with throttle tip in at low speed cruise. disconnecting the KS keeps the ECM from pulling the timing back with knock and will make it easier to perceive the slight pinging that will indicate that the timing is too advanced. if it pings, decrease the timing incrementally until it doesn't.
with mine I've incrementally bumped the base timing up a few degrees then run a tank or two through checking mileage. at some point, when it's too advanced, mileage will drop as a response to the ECM/KS pulling timing due to knock. I have a fairly rigid commute to work and back that takes many of the variables out of my mileage checks though.
Gotcha, Ill give this a shot tonight and report back.
Ok so tried Timing with KS plugged in and air cleaner. Ran very sloppy through all advance or retarding of timing. To take a step back - if the car has been idling in my driveway for 10 minutes the choke plate should be open right? If I turn the car off and key to on but not start, the electric choke should open the plate?
It's still running crazy rich which is either choke or needle and seat/float issue.
The reason I ask is the only way I can get it to start is to use something to keep the butterfly plate open to lean the mixture and get it to start. Other wise it just cranks until the battery is dead.
the choke will only receive 12 volts when the engine is running. the voltage source is the alternator.
running for 10 minutes should allow the choke to open. a bad choke coil is a common failure though.
try wiring the choke open. make sure the engine is warmed up before disconnecting the four wire connector. it will not idle as well with the ESC disconnected, all else being adjusted correctly. that's why the ECM commands the idle bump solenoid to deploy when it sees the ESC disconnected.
this apparently being a new, or freshly rebuilt, carb. check the following:
TPS voltage near 0.40-0.50 V at/near idle position
Mixture Control Solenoid inside carb clicks with key in 'run' (will stop clicking after about a minute if engine not started)
Travel of MCS measured at 1/8"-a small piece of wire inserted into one of the vents next to the IAB can measure this
IAB and Idle Mixture Screws at 3-4 turns out each.
the choke will only receive 12 volts when the engine is running. the voltage source is the alternator.
running for 10 minutes should allow the choke to open. a bad choke coil is a common failure though.
try wiring the choke open. make sure the engine is warmed up before disconnecting the four wire connector. it will not idle as well with the ESC disconnected, all else being adjusted correctly. that's why the ECM commands the idle bump solenoid to deploy when it sees the ESC disconnected.
this apparently being a new, or freshly rebuilt, carb. check the following:
TPS voltage near 0.40-0.50 V at/near idle position
Mixture Control Solenoid inside carb clicks with key in 'run' (will stop clicking after about a minute if engine not started)
Travel of MCS measured at 1/8"-a small piece of wire inserted into one of the vents next to the IAB can measure this
IAB and Idle Mixture Screws at 3-4 turns out each.
12v verified to choke connector.
MCS will click in the run position
3-4 turns out on mixture screws and IAB
Will verify the travel of MCS and TPS voltage later today.
I did some reading and adjusted the choke break adjustment screw to adjust the opening of the plate to 1/8th from a cold start (it seemed to be opening too much actually, which goes against my flooding theory but we'll see). It started right up this morning, ran for about 10 minutes. I turned it off and it wouldnt start again - flooding issues it seems. I had to head to work so let it be. Perhaps its a leakdown past the wells issue that is prevalent in these carbs? Im going to ask the rebuilder if they sealed these up.
