: i think ive figured out my bad mileage

03-18-05, 09:59 AM
i got a dwell meter yesterday and hooked it up to my car. it read close to or less than 10 degrees when it should be at 30. i looked this up in my shop manual. and it said that this means it is running full rich. now i just need to figure out why it is running full rich, i already replaced the 02 sensor. any other ideas?


DopeStar 156
03-18-05, 03:33 PM
My car had some bad carburetor parts I had replaced and the mileage improved greatly. I think what you're looking at is replacing the stepper motor. Which I believe is the part that controls the idle. My problem was it would idle too low in drive, and too high inpark. Have it checked out.

03-20-05, 06:01 PM
i've got that same problem, so i'll check that out, but i still want to know what would be making it run full rich all the time

03-20-05, 09:40 PM
I know where my poor gas milage comes from. My foot!!! :p

03-21-05, 08:09 AM
lol, a bit here too, but it shouldnt be enough to make me get 8 or 9 mpg

03-21-05, 10:34 PM
First thing is to check codes, but barring that, and with the lack of a data display, you might have to go find a scan tool. Look at stuff like the coolant temp sensor, ambient temp sensor, MAP sensor, and block/learn values. See if any are out of whack.

03-22-05, 07:35 AM
i have a code 31 which i looked up to be the canister purge solenoid, but would that be causing it to run rich all the time, under 10 degrees dwell?

03-22-05, 08:08 AM
Yes it could be the cause. Beyond that, getting back to your carburetor, you have an ILC (vacuum-controlled) that controls your idle, not a ISC (electrically-controlled). As for your use of a dwell meter, I'll assume you're talking about using it to check the M/C solenoid counts. First of all, you need to know that a reading of 10 degrees is toward the LEAN side, not the rich side, and second, you need to know that any reading between 10 and 50 is okay as long as it is "varying". The problem is when you have a "fixed" reading. The CCC system is actually a great system but there are many things you need to know to make sure it's working properly. Unfortunately, this also means special tools and specialized training.
Before we look into the system at all, I need to know what your level of training (experience) is with the system.

03-22-05, 11:05 AM
well, my experience is pretty much none, so . . ., i was just trying to see if i could figure anything out before i took it to my mechanic. the reason i thought it was rich was because there is a chart in my shop manual that shows rich vs. lean, and it showed 10 degrees as rich. maybe i misread the chart, correct me if i'm wrong, also, unless the dwell meter is broken/wrong, it reads a fixed 10 degrees

03-22-05, 01:09 PM
The lean vs. rich issue can be confusing on the CCC system. You need to understand what it is, you're reading. You're reading the actual M/C solenoid activity. In other words, even though a dwell of say, 10 is a rich dwell, that only means the ECM is commanding the M/C solenoid to go full rich. Why? because it is sensing a LEAN exhaust via the O2 sensor. So in other words, if the O2 sensor sees a lean exhaust, the ECM "should" be telling the M/C solenoid to go rich to compensate. I realize this is a kind of simplistic way to describe what's going on but it's reasonably accurate. As far as the "fixed" vs. "varying" description, this refers to system crossing over the stoichiometric "perfect" 14.7:1 A/F ratio. The needle "should" move up and down the scale during "closed-loop" operation (A/F being controlled by O2 sensor input). If the needle is not varying, you should verify that the engine is in "closed-loop". In "closed-loop" the needle moving up and down the scale, shows the bounce back and forth from rich to lean. This is normal, and is the same thing you'll see if watching O2 sensor output. On later ECM/PCM applications, this action of crossing back and forth over the 14.7:1 A/F ratio is kept track of and counted, and are referred to as the "cross-count".
If you're unsure as to whether the engine is in "open-loop" or "closed-loop", a simple test is to create a vacuum leak and watch whether the needle moves on the scale or not. If it moves, you're in "closed-loop", if it doesn't move, you're in "open-loop". If the engine is warmed up and it's still in "open-loop", try operating the engine at about 2500rpm for about a minute or so to see if it goes into "closed-loop". If it does, the O2 sensor is cooling off and dropping the engine into "open-loop". While the engine is in "open-loop", it will run at a much richer A/F ratio so your problem may be that you're just not getting into "closed-loop".

A little background on the M/C solenoid:
The M/C solenoid is what causes that constant "clicking" noise from the carburetor while the key is on. When the solenoid is energized, the primary metering rods are lifted, and when the solenoid is de-energized, the rods drop. So everytime you hear the clicking noise, you're hearing the metering rods being lifted and dropped, which opens and closes the primary jets in the carb. Seems simple but it actually does a reasonably good job of controlling the primary fuel flow through the carb. This is also why you can use a dwell meter to check the M/C solenoid commands, it's simple on-off-on signal is virtually identical to the open-close-open signal that ignition points use.

03-22-05, 04:49 PM
thanks for the great information katshot. if i am not getting into "closed-loop", is there anything that can be done to get it to go into "closed-loop". the only reason i'm trying to figure stuff out is because i am 16 and dont have a ton of money to spend (and parents wont pay for it), and because i enjoy working on cars. so any information is welcome, learning new stuff is great.

03-24-05, 10:34 AM
Force it into "closed-loop"? No, not as I recall. It's easy to force the ECM into "open-loop" temporarily for diagnostic purposes but, only the ECM sets the system into "closed-loop". There ARE several criteria that must be met before the ECM will allow "closed-loop", but first you need to see if the system is in open or closed-loop. Like I said, if the system can't react to a change in A/F ratio like from a vacuum leak, you're in "open-loop". Another easy way to tell what loop you're in is to see where air from the airpump is being sent to. In "Open-loop' the air is sent to the exhaust manifolds and in "closed-loop", the air is sent to the catalytic converter. You can rev the engine while feeling the hoses and tell where it's going pretty easily.

03-24-05, 11:14 AM
alright, i'll check that out tonight. thanks for all of your help