Probably just missed it since my computer skills are minimal, but I've been searching here and with Google, and haven't found any kind of article on doing maintenance on Ford speed density EFI systems. There's a lot of stuff by rodders on replacing the speed density with the later mass airflow system, but I'm not hopping my engine up, for now.

The idle speed wanders up and down in random fashion, and I'd guess either something needs cleaning or replacing, assuming there isn't an air-leak or fuel restriction I've missed ('88 4.9/C6). Surely there is a standard maintenance routine one should probably do proactively on an old speed density EFI; I can find such info for the later system. So far I've installed a new Bosch O2 sensor and disassembled/cleaned/bench-tested the EGR valve. I replaced 5 of 6 plugs; #4 seems to have been cross-threaded into the hole and I don't dare try to remove it until I'm ready to rebuild this engine. Air and fuel filters are new.

I'd be happy to have specific advice, but what I'd really like is direction to an article of doing a speed density EFI overhaul, if one exists. I've got a book on Ford EFI systems ordered from the library, but it won't get here until maybe Saturday.

 

Another question: Does the computer have to reset itself every time the battery is disconnected? Does it start resetting once you hook up the battery again, or does the engine have to be running (as I assume)? How long does this take, and how do you know the process is complete? Again, this is for the older EFI system.

 

Not sure of the specifics of EFI maintenance, like Reseting codes or learnt parameters...


But, check over every connector and vacuum lines would a really good start. Look for corrosion on the electric contacts. Pull the wiring to your IAC valve on the throttle body and have a peek at it. Maybe even pulling the IAC valve off and see if it's gummed up.

 

The efi system is suppose to be maintenance free...now with that in mind, here's what I have done since 1986 (my wife's, then new Toyota Celica GT.....nice car but OMG, some of the engineering- ugg)......

Specific to the intake, every 6 months I use BG products intake cleaner. It's a spray that is safe for the intake coating but it will clean/dissolve the normal crude buildup...but...do not spray it like you degreasing brake shoes......a gentle/light, brief shots (several) is all that is needed because it is very effective and bulk application of this (or any similar product) can damage sensors....yes, pull the iAC and clean it with this as well.

With regards to the injectors, my wife's Toyota...I was having to have the injectors professionally cleaned annually.....so I started running Marvel Mystery Oil in the fuel tank.....I was running 1 oz per gallon (about 1/2 of recommended) and that kept those misters open and functioning fine for the 11 years we had the car......I continue that practice with everything we have today that is EFI. you can also do a 1 time shot ...that works well...and Chevron Techroline is an excellent cleaning product (although the MMO has lubricants in it at a much higher concentration).

 

I would second the suggestion of vacuum lines. If there is un-metered air getting in, the engine will go lean, then the O2 sensor sees it, richens the mixture up a bit, and so forth.

 

Thanks for all the tips! Checking vacuum lines and electrical connectors is S.O.P. for any vehicle, and yeah, the first thing I did after getting the van running was to drive over to the Chevron station and fill the tank.

THAT was good for some excitement! As I get in the driver's seat a guy runs up and says, "You're leaking gasoline all over!" I look, and there's gas POURING out all over the asphalt! The guy had driven off quickly, so I ran into the office and told the manager I needed him to push me well away from the pumps (I didn't dare start the engine.). That done, I looked again; couldn't tell for sure, but thought the tank might have a split seam. The gas was still pouring out, but away from the van itself (and nowhere near the pumps). With nothing but bad options, I started the engine and drove the ten miles home; luckily any lights were with me. At home I discovered that the cowboy who previously owned the van had ruined the big o-ring when he had the electric fuel pump out of the tank. Of course he never thought to mention to me what happens when you fill the tank! Fixed now.

One thing I've read is that the gizmo with the moving vane (I forget its name) needs to be cleaned, but that you should do it manually with a rag soaked in carb cleaner, and not spray carb cleaner in it. Maybe first I'll see if the Chevron gas has any effect.

FWIW, I HATE and DESPISE the practice of putting the fuel pump in the tank!!! When I was 16, I could change a fuel pump ($6) in twenty minutes or less; two hoses, two bolts, easy to get at. That was 1962. Now it's all day, for a $150 electric pump. Know what? EVEN IN 1962 THERE WERE ELECTRIC FUEL PUMPS, BUT THEY WERE NEVER IN THE TANK, YET THEY WORKED PERFECTLY WELL. Sorry, it bugs me.

 

Something's weird with the site now, or maybe it's the new Win 10. When I post something, I don't see it added to the thread immediately, as before, but I have to go away from the thread and come back to see if my post actually was added . . . ???

 

You shouldn't have any gizmo with a moving vane. The old speed-density systems don't measure incoming air per se, like the '96 with a mass air meter. The system gets input from the vacuum sensor and O2 sensor, and a few others (temp and so forth), and runs the engine from stored tables.

The idle air control (IAC) might be amiss in yours. That meters some air past the throttle blade at idle. If it is dirty or just old and not working right, less than premium idling could occur.

Also try wiping down the throttle blade itself. Some oil or other gunk can get on it, and change the effective opening size, leading to poor idling. Some years (not sure when it started) have a protective coating that is supposed to reduce buildup, and spraying carb cleaner or similar removes the coating, which you don't want to do. My old Crown Vics with EFI 302s had the breather from the valve covers plumbed right in front of the throttle blade, upstream of the air filter, and had this issue.

 

Thanks, Mike.

 

Idle issues on an EEC-IV system seem to trace back to either the IAC (Idle Air Control) of the ECT (Engine Coolant Temperature) sensors.

Of course, old cracked vaccum hoses will give you fits too, but they tend to give either too high or too low idle, not really the surging noted.

My 88 doesn't idle right, but I don't really use it enough to tear into it at the moment (well... i WAS planning on it until I had to redo the rear axle seals and brakes; time to save up a few $$s again). It will often surge or stay at higher than needed idle. When it's warm, it tries to idle at 300-500 rpm right away. I actually think that the fuel pumps might be going and are having a hard time getting enough pressure to the rail to avoid boiling on hot days.

The IAC is easy to full and check. You can supposedly clean them, but it seems like cleaned ones don't go too long before clogging up again. The ECT isn't bad either. It's on the thermostat housing. I have heard of corroded connectors or even connectors that simply fell off and needed to be put back on. I would think a bad ECT would keep the motor in open loop mode thing it's never warming up (should result in noticeably poor fuel economy).

Speed density systems are pretty easy to troubleshoot. Basically, they sense the pressure in the manifold and look up fuel maps based on that pressure. Because they never measure airflow directly, they can on'y infer how much air is flowing based on the pressure. Any leaks in the system will lead to surging/high idle. The common failure point is vacuum hoses and intake manifold gaskets.

The Fords also do see fuel pressure issues in this era. My F150 sees it. Several 80s Ford Tauruses the family has owned has seen it. The pumps basically require that you keep at least 1/4 tank of fuel to keep them submerged and cool. Then they get into air, they got hot and can get weak. This can affect almost any in-tank fuel pump, hence why a lot of folks say to go no lower than 1/2 tank.

The poor man's diagnosis for fuel pressure due to weak pumps is to turn the key to run and listen for the pump to run for about 5 seconds. Turn the key off and repeat a couple times to build up pressure. If it starts right up after a couple pump cycles, the pump is probably weak.

 

What mine does (and like you I've been addressing other, more immediate problems) is that it will start and idle okay, but after maybe 20 seconds it will randomly start dropping rpm, eventually with the engine quitting entirely. While it's in this condition, I have to hold some extra throttle until it warms up further and stops doing that. And it always sounds a bit marginal when going down a long hill against compression, though it hasn't actually quit on me in hose situations. It seems to maybe be getting a little better since it has been getting some exercise with a fresh tank of Chevron.

No, I don't have Chevron stock, but have seen Mercedes Benz service bulletins from the early '70s recommending use of Chevron with their old mechanical fuel injections. And a friend who was a long-time auto mechanic said that he had seen more than one instance where at his suggestion a customer would run a couple of tanks of Chevron through his car and have fueling problems clear up. I guess that "Techroline" must be a very effective detergent package. I do like the idea, above, of regular use of a little Marvel Mystery Oil (and BTW, what's the mystery?) in the gas; when I had a Mercedes with the old diesel-engine-derived mechanical injection I used to add a little 2-stroke oil to the gasoline very few tanks.

 

The Chevron Techron fuel additive is quite effective. No Chevron stations in Wisconsin that I know of, but bottles of additive are easily located at Wallyworld and similar.

I usually use Top Tier gas, supposed to have a strong detergent package. The chain I buy most of my fuel from has a guarantee to fix fuel related problems from using their product.

I also endeavor to keep the tank at half or fuller. My dad taught me that, and practiced it. He never had to change out any of his own fuel pumps, just customer cars. On the 96 Sable I bought from him, the fuel pump outlasted the tank itself. We put a new pump in when replacing the rusted out tank.

 

The Techron Concentrate Plus Complete Fuel System cleaner works very well (Redline SL-1 works well too). I used a couple bottles when I got my F150 because it was one the recommended to try and clean varnish off the fuel gauge senders. It didn't really fix that issue, but did clean up idle a bit.

I have found it works well in lawn mowers and my Motorcycle that are prone to gumming up the carbs.

As for the idle lowering after startup: It sounds like a bad IAC to me. On of the steps to troubleshoot an IAC is to unplug it; doing so should cause the same thing you are describing.

 

Is the IAC one of the devices that a guy ought to simply replace at say 150-200Kmiles whether or not you are seeing anything dramatically wrong with the old one? I was told that this was a good idea for O2 sensors, so I did replace that before I even got the engine running. The same thing was suggested for the EGR valve, but since that device is mostly mechanical and I'm a cheapskate, I disassembled and cleaned it.

(re. my own rant about modern in-tank electric fuel pumps, and the suggestions that you probably should keep the tank at least half-full to cool the pump, doesn't it seem like a really DUMB system that turns your 20 gallon tank into a 10 gallon tank??!!)

 

Not sure I would just do it because of age. They will all fail eventually, but I'd wait until it goes to replace. Replacement parts these days can often be a pain (my "new" wheel cylinders has 9mm bleeders instead of the factory 3/8" bleeders).

In your case, just unplug it and see if there is any difference in the truck running. Even to just inspect it is easy, since it's on the intake tract and only held in by a few bolts. If it's all carboned up, probably should replace it.