Thread: Odd running/ stalling issue.

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One of my daily drivers is an 84 Crown Vic Ford with 302/ CFI engine. Only has about 77,000 miles on it and generally runs strong and well. But over the last few months it has started developing a running problem. It happens most when I am slowing down for a redlight or going slow over speed bumps. If the road has a washboard surface the engine bucks just as if you were rapidly turning the key on and off.............kind of like if you had a stick shift car can forgot to shift down, how the motor would buck.

If I go over a speed bump it will even stall sometimes, but most times it just stumbles a few times then smooths out. If I am going through a construction zone where the pavement is very rough it will do it too. The guy at the auto parts store mentioned the MAP sensor, but I don't want to just start throwing parts at it. Oh, it stalls the most when I am making a sharp turn like parking in a shopping center or exiting a street, probably because of the load of the power steering pump?

When it comes to trouble shooting one of the newer cars (not that 84 is newer, but my expertise ends at about 1970 ) I am lost with all the sensors , computers, and fuel injection. Any suggestions you guys who know this stuff have will be appreciated.

Don

Most places like auto zone will hook up a scanner and be able to read the codes to tell if its a bad sensor,not shure on that year what type of computer it has...might be obd1.

A good scanner is a valuable tool in these type of engines.

I would say start there.

ha don I have had some experience in this area when I had my shop and taught auto emissions at the j.c. I know this will sound crazy but all fomoco service and tech manuals start with what ford calls a wiggle test ( honest I not making this up ) before you do any diagnostic testing bring the eng to opp. temp. and wiggle all the connectors you can find including the bulk head conn. at the fire wall and the ecm conn. that one do last because it's not easy to get to if the motor stumbles you have found the prob. clean the connector if that doesn't fix the problem we will go to step two good luck .....ted

don b.t.w. I don't think this is a sensor problem I think its an actuator......ted

yup.. Ford's got the " wiggle test ".. my scanner ( OTC monitor 2000 ) has a test mode to check systems while performing the wiggle test, and it beeps and shows an error code if somthing amiss happens while wiggiling.

Thanks for the ideas guys. I wasn't ignoring anyone, I ran to the shop after I posted the question and just got in.

That wiggle thing makes sense. It must not take much to cause whatever is going on because any bump or rough pavement sets it off. Even slowing down does it. I'll have to get in there and shake things around a little. Then I might head to autozone if that fails.

I appreciate the feedback.

Don

X2 on Ted's suggestion. The mid 80's Crown Vic was notorious for loosened wire connectors and harnesses because of substandard wire production and the inability to withstand years of vibration.

don the next step is if you have problems when back peddle is a dirty I.A.C.V. that's idle air control valve, you can remove it and clean it and the air passage with spray carb cleaner, the iacv controls idle and also acts as a dash pot to over come a sudden mixture change at throttle closure, the computer looks at r.p.m. and eng. load from the map sensor and controls the air that goes around the the throttle plates, the iacv supplies air because the throttle plates are completely closed at idle. if that fails to correct the problem we'll have to go to step 3 good luck let us all know what happens....ted

Thanks, I'll be trying all of that. It also does another thing. I can be sitting at a redlight and all of a sudden the rpms just drop, like it stutters or something. It generally recovers and keeps running, but at times has stalled. Always restarts immediately though.

Don

don that sounds like the iacv is dirty. the computer See's the rpm drp and compensates for it be sure you don't have a vacuum leak first but I'm sure you checked that first......ted

Don the first thing I thought of was a loose battery. I had one in a 84 CJ7 that would jump on bumps and arc to the hood, causing similar power fluxes. Next would definately be a loose ground which would limit connectivity, making the problem exagerate with bumps, or increased power loads, like the power steering, lastly the idler thing could be a simple smog valve come loose, also had this problem on the same Jeep. It would idle way up and down at stop signs, after driving for a while on the highway. Turned out to be a disconnected 2 dollar valve. Cost about 400 in replace junk, before I found a smart mechanic!

To be honest, I haven't even popped the hood to check it out, but I have also thought maybe it might be a ground wire or battery cable. The way it acts is as if you are momentarily shutting off the power.

Problem with me is I like building them, but hate working on one I have to drive every day. Luckily my Honda still runs great, so I can take my time and try some of the suggestions you guys have given. I usually only drive the Ford when I have an engine or something big to toss in the trunk.

Don