"85"CFI Merc runs good,then runs then runs like crap and won't start for a while.

[Mercuryman]

Hi,I have a 1985 Mercury Grandmarquis with the CFI 302.When I first start it,it runs good for for about 6 or 7 minutes,then it will start to gradually start to run really crappy and stall about 3 or 4 minutes later.It usually won't start after it stalls.After sitting for a few hours it will start and do the same thing again.

So far I tried swapping out the throttle body with one I had from the junkyard.It ran the same with the junkyard throttle body,so I put new fuel injectors in my original throttle body(thinking the injectors were the problem)and put it back on the Merc and it does the same thing.I also swapped out my TFI ignition module and the coil,with one from a "84" Lincoln and that didn't help either.Also It has new spark plugs and wires.

Any advice will be appreciated
Thanks

[jpc]

Any computer codes? Any chance it's overheating? Have you checked the base ignition timing?

[jpc]

Could the warm idle speed be set too low? These cars have a mechanical thermostat and fast idle cam (similar to a carb setup) that gives you a high idle at cold start, then a lower idle after running for a few minutes.

[Mercuryman]

I Did have a code reader at one time,but I am not sure where I put it.I have not used one.How do they work?
The last time I checked the timing was 2005.
It does not have a temp gauge,so I'm not sure if it's overheating.I suppose I could install one.
How do I check the warm idle speed?

[jpc]

See shorty's post about setting high and low idle. With nice pics.

I bought an Actron code reader for about $15. It plugs into a diagnostic port near the top of the driver's side shock tower. It comes with a manual that tells you how to do a scan. Once you have codes from it, google will translate them. It's not an OBD II scanner for our cars, they use a Ford-specific protocol that needs a Ford-specific scanner. The scanner knows many things. It can tell when you need a new O2 sensor that makes every tank of gas go 80 miles further. So it can pay for itself.

I installed a temp gauge, I like to know that the t-stat is working.

You might want to check timing again. The timing chains stretch out over time and that causes the timing to lag, if it was set perfect in '05 it might be a few degrees behind.

[gadget73]

you can use a test light and a jumper wire to get codes. The cheap code scanners are little more than this. The digital display ones are nicer but if it just beeps at you, you can do that for free.

http://oldfuelinjection.com/?p=13

The problem sounds temperature related. 5-10 minutes should be enough to get into open loop mode where it starts to use the oxygen sensor to do fuel trim. If the sensor is bad, it could be making it run so rich or so lean that its dying. You likely will not get a code for this. I've actually never once gotten a legit oxygen sensor code. Any time it gave me a code related to the sensors, it was telling the truth about a lean or rich condition that was caused by something else. When they go bad, it just spits out a code 11, all is peachy. The CFI oxy sensor is cheap, and usually it doesn't cause bad running when it fails. It just sucks gas like crazy with no other obvious symptoms. For the 18 bucks or whatever they cost, its probably worth a new one.

I'd also replace all of the vacuum lines if you haven't yet. Change the timing chain too when you have a chance. The one on those engines got very sloppy and when it jumps, it will ruin the heads. 302's are interference engines. If you haven't, change the fuel filter and give it a tune up too. It may not be the cause of the problem, but fuel filters are frequently neglected and these do run better with plugs that aren't burned to a crisp. Change the wires and the cap if they are old, or at least clean the cap so its not scaly.

[sly]

I wonder if the choke is choked. Does CFI use a choke for cold starts?

[fmansfield444]

I wonder if the choke is choked. Does CFI use a choke for cold starts?

There's something that the manual calls a heater choke or choke heater on the passenger side of the throttle body, it has a single wire connector to it

[gadget73]

Its half a choke. It has the high idle part, but not the air door part. If that was jammed, either it wouldn't have high idle, or it wouldn't have low idle.

[sly]

I wonder if the timing is shot then and it just needs a new timing chain/gears

[gadget73]

could be. Easy to observe with a timing light. If the chain is that bad, the mark will dance around. If it actually jumped, the motor wouldn't run though.

[sly]

true.

[Mercuryman]

I just got a universal Bosch Oxygen sensor for $16.99 from Auto zone.I figure it's worth a try.

The spark plugs and wires I replaced a couple weeks ago.About a month ago,I also replaced the gas tank,gas tank straps,fuel pump(it quit working)gas gauge sending unit and the fuel filter.The gas tank was rusty inside,it was leaking.The sending unit and fuel pump I got from the junkyard for 1/2 off for $12 .All the other parts I replaced were new.

The car has been mostly sitting since 2005.Largely due to this problem.

How many miles do the original timing chains last?

[gadget73]

on an 85? about 80k miles before they get floppy usually. They jump around 110k and destroy the engine. The design was changed in 1986 to one that will go easily 200k before it gets loose enough to even be a concern.

[lincolnlarry]

Not the timing chain if it runs well when cold. Stretch won't get larger enough to run bad and stall when hot. Then when it jumps it will run bad hot or cold. Not sure what it could be from info.

Just for fun, pull off your distrib. cap and see if there is any play side to side In the dist. shaft when cold then when it stalls.

I would even wonder about heat related coil problem.

Hope some of this helps....