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1981-1983 Imperial Fuel Injection Tour - Running Rich

Imperial Home Page -> Repair -> Fuel -> 1981-1983 Fuel Injection -> Running Rich


Question from Brian:

My car runs as if its running WAY rich... lots of back smoke, poor idle, poor acceleration, etc., like a stuck choke on a carburetor. I have been told that its the air flow sensor located on the throat of the breather. Any ideas ???


From Frank:

I'd bet on the airflow sensor. The fuel flow sensor sometimes can give this problem if it's gummed up. Has the car been unused for a while and now, upon starting to use it again, the problem occurs? Anyway, of the components involved. The airflow sensor is the easiest and least expensive to change.

If the airflow sensor does not help, run some fuel injector cleaner through the system in the event that the fuel flow sensor is sticking. I never tried to get access to the sensor, I just replaced the support plate when I had problems with it. You may not want to do that on a whim since a rebuilt is about a grand.

WARNING: If you engine is running as rich as you state, it may be dumping raw gas past the rings and into the crankcase where it gets circulated with the engine oil. This causes a number of problem with seals, and also weakens the fibre coating on the camshaft and crankshaft cogs. Then the timing chain slips. Then the valves get bent. (Yes, the 318 is an interference engine.) Check you engine oil, if it smells like fuel, or is very dilute (thin), or if the "oil" is over the full mark on the dipstick, you are looking at a really expensive problem in the making. A friend's 81 Imperial did this to him and we ended up changing:

Airflow sensor
Support Plate
Timing chain
Crank and cam cogs
Left and right side intake and exhaust valves.

Doubled the cost of the repair and took a heck of a lot longer to do.

Question from Brian:


Just before the duals were installed the car failed to start. it was flooding really bad. someone recommended removing the air flow sensor and cleaning it, he did and the car ran great.  Better than it ever had.  With the car running well he decided to install the duals. The car ran well for a very short time after this, then it failed to start again. Again the sensor was yanked and cleaned, and ever since the car has been VERY hard to start, puffs the black smoke and basically runs like crap. It flooded so bad it filled the crank case with oil. Hears the kicker though, occasionally it will fire up and run perfect for 10 or 15 miles and then crap out again.

I'm sure the pipe was cut just before the Y and pipe ran from each manifold pipe back. Trashed the converter and anything behind the Y. . The manifolds were left intact, no headers. Very good quiet mufflers were also installed and the pipes were ran to the back bumper. Is there no way to check the air flow sensor as no substitute is available ???

I would like to keep the EFI if at all possible.


From Dave:

It could be a problem if, in the process of installing the dual system, the installer left out/damaged the oxygen sensor which is an integral part of the fuel injection control system (computerized). I have had experience with a great many engines of all makes, and none of them will run well, if at all, with a bad/missing sensor. 

From Dick:

I cannot think of any way to test the air flow sensor.  It appears that it is telling the computer there is way too much air going through the snorkel.  Perhaps the little diaphragm got damaged when the cleaning was attempted.  I cannot see how one could clean the sensor, it is just a dip tube which samples and reports extremely small air pressure differences.  The sensor itself is encapsulated within the electronics module, and the tube would not be likely to get dirty.

It must be nice to be able to modify the exhaust system like that without big brother grounding you.  I have no experience with modified systems, so I am kinda at a loss.  Perhaps you could find a vendor that would let you return the sensor if it does not do the trick. If you do replace it, and the old one is bad, please don't throw it away.  Some of us (including me) would give our right thumbnail for a chance to take one apart and see what makes it tick.

Another from Dick:

Very likely this is related, if not the whole cause of your problem. The exhaust system, including the catalytic convertor, the O2 sensor and the air switching system all rely on the exhaust system being exactly as designed.

Did you also put in headers? If so, what did they do with the O2 sensor? How did you split the exhaust? Do you have two converters for a real dual system, or did you just split the exhaust pipe behind the converter?

All of this would certainly affect the back pressure, which has to upset the CCC. Hope you saved the original parts, at least for a pattern as to where to put the air injection tubes and the various feedback points of measurement for the EFI/CCC

If not, and if you live in a state where you could get away with it, you probably should swap your EFI setup for a carburetor conversion at this point, I think it would be tough to recover the original design at this point.


Follow-up from Brian:

How do I check the anti-stall valve ???

Reply from Dave:

Unfortunately the anti-stall valve cannot be checked per se. It is diagnosed by symptoms. The main symptom is upon start up, usually a larger black puff of smoke which goes away after warming up. The next easiest symptom is while rolling down the open highway slam the gas pedal to the floor, there should be no hesitation, and assuming everything else is tuned properly, if there is you can be relatively safe with a firm belief that your anti-stall valve is shot.

But, let us not be too hasty. Are we talking about the same car with the possible O2 sensor problem..?????

If so, let us discuss some options regarding that problem. Mopar engines have always been some of the strongest around (some say the strongest) but, what has made them such great engines is the precision tuning that they go through in engineering. By putting dual exhausts on your Imp you have effectively reduced the back pressure, which is fine for some engines, however, Mopars are designed to have back pressure.

Unless you installed tune pipes and mufflers, after carefully calculating the necessary lengths etc, then your problem may well indeed be your O2 sensor. Effectively changing the back pressure in your exhaust would give the sensor a false reading due to excessive air (exhaust flow) by the sensor. This would not allow the sensor to transmit an accurate reading to the computer and what would be most likely to happen is that the sensor would tell the computer we need more gas. Do you follow what I'm saying??? I hope so! Thus producing the black output due to a 'Too Rich Mixture"! This is Hi-tech stuff I love this stuff.

Now the fix, of course the obvious is to go back to a single exhaust system, but I'll assume that you do not want to do that. So, the other way is to install two new mufflers with greater restriction, effectively increasing the back pressure. Or, adding resonators near the end of each tailpipe assembly achieving the same effects as the first fix.

One of the greatest problems we meet with reconfiguring the newer engines with a computer system is that we have to rematch the computer to our adjustments (or live with the originals). Rematching the computer system is just short of impossible, unless you eliminate it completely which is what I have done to several cars. Of course, this is not cheap and in some/most states it is illegal (Big Brother).

Once this is done however your 440 will run like you have never thought possible, the late '60's early '70's are examples of just how powerful these engines really can be when done properly. The 60/70 model 440's are still sought after by race mechanics from the drag strip to the off shore boats. Of course the 383's are still great engines and if anyone wants a new one, give Direct Connections in Chicago a call, they are still available.

Enough said, I'm starting to ramble, just my Chryslerholicism coming out. If it's performance you're looking for and you are necessarily worried about keeping your Imp original, give me a call 1-616-946-9431 or e-mail mark Private a Chrysler engine hasn't been made before '85 that I can't get the most out of, usually with very little work, they are great engines and if tuned properly and kept maintained will last for a very long time.

Question from Imperial61:

Does anyone have a good understanding of exactly how an O2 sensor works?  I could be wrong, but it seems to me that since the sensor measures the fuel content of the exhaust, the actual amount of flow past the sensor shouldn't matter since the content remains the same regardless of how much is going by.


From Dave:

The O2 sensor in a vehicles' exhaust is a large thermocouple (a device that generates a small voltage when heated) that sends a signal to the computer based solely on the temperature of the exhaust gas as it passes the tip of the sensor. Basically, the leaner the engine is running, the hotter the exhaust (and the whole engine, by the way) will be, and vice-versa. The hotter the exhaust gas, the higher the voltage generated by the sensor.

My fellow aviators will corroborate this, since piston powered aircraft have had manual mixture controls almost since the beginning of flight (necessary before the dawn of computers for the same reason that cars lose power as they go up a mountain...the air is scarcer up there and the engine starts to run progressively richer as you go up the hill, until you stop and perform a carburetor adjustment. Not very practical in an airplane!).

On the ground, ready for take-off, the mixture is set "Full Rich" (at sea level) in order to produce full power. It also provides extra cooling for the engine (air cooled engine producing max power at low airspeed gets hot in a hurry). You can actually watch it happen if you happen to have an exhaust gas temp gauge (some aircraft do).

The same thing happens in a car. Running way lean, an engine runs much higher combustion chamber temps and is very susceptible to "detonation" (not to be confused with spark knock or "ping" which is brought on by too much timing advance). This detonation is EXTREMELY damaging and can literally destroy an engine in very short order. On the other hand, running way rich for any length of time fouls spark plugs, washes critical lube oil from the tops of the cylinders (creating a big wear problem) and creates the galloping idle, low power output, lousy gas mileage and black smoke that the car is experiencing.

Just because the O2 sensor is there doesn't mean that it is working correctly. You can check it with a digital volt meter by placing the positive lead on the pigtail connector of the sensor and the negative lead to a good ground. As the sensor heats up, the voltage (which will be in the millivolt range) will gradually increase. Check the proper values in the emissions troubleshooting/sensor tests section of the factory manual.

If you don't have one, call the service department of your local friendly Chrysler dealer and ASK! I have found that they have been very helpful when I've had a service question that was not covered or unclear in the manual.

 Question from Brian:

Would the O2 sensor make one run rich ???

 Reply from Dave:

Yes because if there is no signal from the O2 sensor, the computer uses baseline parameters for what's called the "limp-in" mode. That includes a static ignition timing signal (i.e. no advance) and a pre-calibrated fuel mixture. Keep in mind that this pre- calibrated mixture was determined for the stock exhaust system and that your dual installation has changed the flow characteristics for the entire engine.

The reason that the car may run OK when it is cold (i.e. that first 10-15 miles) is that the com-puter uses a different set of baseline parameters for what GM calls "open loop" ops, until the temp sensor warms to at least 100 deg F and the O2 sensor warms up enough to start generating a signal. Once that happens the computer goes into "closed loop" mode and if any of the sensor signals are missing/incorrect for the con- ditions, will go directly into the "limp-in" mode. When this happens you should receive a "Check engine", "service engine soon" or "power loss" light from the computer. If you're not then check to make sure you have a good bulb in this socket.

I don't think Chrysler Corp computers are this way, but if you remove the bulb (or it burns out) in a GM car of that era, you will toast the computer in short order. 

From Dick:

I do not have any personal experience with running one with no O2 sensor except for a few minutes. I think that from the way the system is programmed, the car would run normally for the first few minutes (the computer ignores the O2 sensor input until it warms up), then results should depend on the current atmospheric conditions. I would not expect a big difference in drivability, but someone with personal experience could probably shed some more light on this.

This page was last updated September 2, 2001.  Send us your feedback, and come join the Imperial Mailing List - Online Car Club