Question from Chip Hood:
I have been following with great interest the problem that Carl Baty has been having with his '81 Imperial to see if it might be related to one of two problems I am having with my '81. If anyone knows of the cause or has any suggestions toward the following, it would be greatly appreciated. The first problems is the car suffers from a very erratic idle if the car has been idling for some time. The car has the EFI intact and has 46K miles. Under normal driving, traffic lights and stop signs do not seem to cause a problem. But if I'm in heavy stop and go traffic or the car has been sitting idling for some time (2 minutes plus) the engine will almost stall, then rev high, then smooth out for a while. It will continue doing this at erratic intervals. This happens regardless of whether the car is in gear or in neutral or park. The car runs fine otherwise.
The second problem is a very loud fuel pump. The radio or road noise will drown it out, but if you are sitting in the back seat it is very annoying. The car was a late '81 so it has the '82 fuel tank and pump setup.
Though I haven't completely ruled it out, I though I might have a fuel pump going bad causing both of my problems. But most people I have talked with say that when a pump goes out, it goes out out completely. So I'm stumped. Any suggestions?
Reply from Dick:
Your problem with the erratic idle is not going to be easy to track down. I think the first thing to do is to replace the O2 sensor, since this only happens at idle, and only when the car is thoroughly warm. Another possibility is the EGR valve or its controls, but the O2 sensor is so cheap and easy to change, (and is certainly due if it is still the original) that I would tackle that possibility first. If that does not cure the idle problem, then we will disconnect and plug the vacuum line that goes to the EGR valve to see if that affects the problem. Lets take those first steps and see where they lead us.
On the noisy fuel pump; these cars all have a noticeable whine from the fuel pump, which is worse in the back seat. When the car has accumulated many miles, or if it has often been driven with a low fuel tank (below about 7 gallons in it), the bearings in the pump get hot and wear, and begin to get much more noisy. Your car does not appear to have enough usage on it to have worn out the pump, if the odometer is the original and does not show the asterisk. It is possible, though, that your fuel pump is failing for some other reason. I have one '81 which has high mileage (probably over 200000) and a very noisy pump, but the noise only occurs on very hot days, (which in Temecula unfortunately occur quite often). It has the worn bearing syndrome, and I am about to convert it to an externally mounted pump, which I did successfully to another of my '81's a few years ago after the original pump split its housing. Unfortunately, after the conversion (to a Mustang 5.0 liter pump), I can still hear the whine, even though I rubber mounted the new pump and tried to isolate it acoustically as best I could.
I am quite certain your two problems are unrelated, by the way.