Hey fellas, my 1980 Eldorado, when decelerating on approach to a light or stop sign, is cutting out completely. I re-start the car and some of the time it continues on without issue, and other times will stall again at the point of re-start as soon as I put it in gear. Fuel filter has recently been changed and, other than that, it is running impeccably. Any comments/advice would be greatly appreciated
Thanks
Steve
I assume this is the 6.0 liter DEFI system? Its got the MPG monitor on the dash?
Other options were diesel, V6, or the CA option which was the Seville's 5.7 w/efi. None of those had the MPG thing on the dash.
So assuming the 6.0 DEFI. Any check engine light / trouble codes?
I don't have time to grab the manual so I am working from memory but I believe the idle control on those was a an 'steeper' motor that acted as the stop on the external throttle linkage. One of the common issues with that style was they had switch contacts in them that 'sensed' if the throttle was closed / touching them which then told the computer that it had control. Sometimes at least on the carb systems if that switch went wacky the computer got confused and did wacky things to the idle speeds. I seem to recall there was a fairly simple test for the assembly that involved a ohm meter and a 9v battery.
At this age a fuel pressure regulator or general debris or leaking in the throttle body is common. The regulator is part of the throttle body assembly. There are O rings that seal the injectors into their mounts. A little leak could be dumping extra fuel into the engine and confusing the computer. Same thing with the regulator. Could also be debris built up on the inlet screens on the injectors themselves restricting fuel so again the computer can get confused. All of that is fairly easily solved / eliminated with a throttle body refresh kit. It includes new O rings and regulator bits. If its not been done recently that you know of it may be a good thing to do just so you know its not a problem or going to be one soon.
Another possible issue is fuel pump getting tired or having bad electrical connections. I have seen em get weak or actually cut out when the system voltage drops. You could have a weak battery or alternator and when you come to a stop the system voltage drops just enough that the also weak fuel pump can't quite keep up. This one is harder to track down since I don't think there is a nice easy place to tap in and check fuel pressure on these. There was one of those infamous J tools that the shops used to 'splice' into the fuel lines to check fuel pressure on these.
Those are the first thoughts off the top of my head. I'm tied up for a few days but if you don't make any progress I can pull out my 80 books and have a closer look at things. I also have the 80 electronic diagnostic book which has some very detailed troubleshooting that is not covered as well or at all in the regular service manual.
Another thought I forgot in the last reply. MAP sensor. I don't remember where they put it on that engine but check the vacuum line (or O rings if its directly on the manifold) and electrical connection to it. IF the MAP signal to the computer is not accurate the computer will be confused and not sending the correct timing and fuel info to the distributor and injectors.
Idle and deceleration are 'tricky' areas for an engine and emissions so it could makes sense that it goes down the road reasonable well but has trouble at idle.
How does it start and idle cold? If you were to drive it right away without an extended 'warm up' would it still do this? Thinking maybe a coolant sensor giving bad info to the computer?
Idle control motors were troublesome on the from day one. You should see the contact shaft screw in and out slightly as it controls the idle, if it makes a grinding sound it is usually bad.
Thanks guys. Appreciate you taking the time out to help. Dropping it off tomorrow, will print this out and give to mechanic. Should be a big help
You must determine which engine it has. Is it a V8? Is the distributor in front or
in the back? Bruce Roe
Guys, update.. it needs an idle speed control motor. Found a few aftermarket, but connector plug wont fit. I would rather not modify the wiring harness. Does anyone know where to get a GM ISCM? Also needs a MAP sensor. He is having a hard time finding the ADL connector as well. HELP!
There is no aldl link your car uses it's own obd thru the ac control head.
Thanks Dave