Ok I am finally ready to throw in the towel and install a manifold and carb, in other words...dump the EFI. I can do this no problem with reclaimed parts from an earlier 302 (5.0). I'd like to retain the EFI but after years of pulling codes and chasing issues, not getting anywhere. So I thought i'd ask for help.

Here is what I cannot seem to solve and what I know...

Almost all the sensors have been either replaced or tested and seem to be in spec including the harnesses.

Someone before me removed the air pump and related hoses.
Also the cat is long gone.

The problem that I cannot seem to solve... In neutral, the truck idles great but in if I rev it to 1500 or so and hold it there, it runs fine for a few seconds then rpms drop about 500 and it starts to stumble.

I discovered if I disconnect the (perfectly operating) TPS it revs fine.

But....

In gear, its not drive able with the TPS disconnected.

I get KOER codes of 25 and 44. And its expected that it sees there is no air pump. Can the issues with the Knock sensor cause the problems I'm having? Doubt it but that part is no longer available anyway.

You guys are the experts and I'd appreciate the help. Really would like to keep it original but need it to run reliably.

Thx!

 

Always your call, but I would never trade EFI for a carburetor.

Have you considered checking inside your ECM for the leaking capacitor problem? Lots of threads on this here and in the Bricknose/OBS forums. Those weird problems are often solved by replacing the dried out electrolytic capacitors in the ECM.

BTW, no knock sensor on your engine. That's OBDII stuff.

 

My diagrams show a knock sensor for these trucks. That would be the code 25, but don't worry about that too much.

Code 44 is because the air pump system is not working.

Check all the basics. I have been in the same boat as you with these EFI systems, and I always tend to blame the computer or the wiring or the sensors. But if there are no serious codes(those are not serious) then I would check the basic things;

Check the fuel pressure. Should be around 38 psi, and it will increase a little bit when the throttle is opened. Hopefully you have a shrader valve test port for the fuel pressure guage. Some of these early trucks didn't have them though, so you might have to make a tee and tap it into the fuel supply line.

Check the timing. Pull the spout connector and at idle set the timing according to the sticker on the radiator support, it's usually 10 degrees BTDC. If you have already done this, then just for experimentation, turn the dist a little bit one way or the other and see if it makes any difference. Harmonic balancers are known to slip, and that throws the timing marks off.

I fought a little 86 Ford ranger for 3 years with the older EFI on it. It was driveable, but idled very rough and wanted to stall on take off. I messed with everything on the EFI, I kept blaming it. It turned out to be a poor ground to the ignition coil causing a weak spark. After cleaning the grounds and the outside of the coil off, it runs like a champ.

 

Thanks, yes I could write a book on the things I have checked or done related to this truck and the EFI. The guy I bought it from, or someone before him, had their own fun. When I got it I figured all the problems were because I found the O2 sensor wire was broken off. Replaced that and it ran better of course. Still had big random idle issues. Some days smooth as glass, other days a monster to keep running at a light. Nothing seemed to cause all this such as weather or temperature. Fuel pressure was one of the first things I tested... even taping the gauge to the cowl to monitor it for a few days. was sure this was the issue. But no. Literally have changed out all the sensors and actuators minus the knock sensor. Like I said in the first post, the Air pump and hoses are long gone. The only obvious clue it was ever there is the bracket that held the pump. I went to the bone yard and pulled another ECU from another 86 last year. Its possible both have the same issues but there is no difference from one to the other in the way the engine performs. So sort of have ruled an ECM issue out somewhat. Truck runs and drives better than it ever has but just have this one lasting problem i can't seem to figure out. If it was a carb engine I would immediately go for fuel starvation. That's what it acts like. Here's the thing I noticed today. Farting around with it I was testing the TPS today with a meter. All within specs. a little less than 1 volt at idle and progresses smoothly to about 4.75 Volts at full open. Ok so I thought "what would it run like disconnected?" Tried that and it started fine idled fine and ran smoothly at 2000 rpm too. But trying to drive it disconnected it sputtered and stalled as soon as i tried to accelerate away. Obviously the ECM knows the truck is in gear and looks more at the TPS for feedback than it does in neutral. With the TPS connected and in Park It idles great but if I rev it to 1500 RPM or so it's fine for about 10 seconds. Then its like something suddenly kicks in and it drops 500 RPM and runs rough. Still comes back to idle ok and is fine there. I can then rev it back to 2000 RPM hold it there and it does the same thing. Very strange. But I hoped someone out there may have had this same issue so I decided to check. Always open to new ideas. Thx

 

Oh yeah. A couple of things I should have added. There is a Knock sensor but Ford and the aftermarket no longer makes a replacement so I figured it was not a big player in the scope of things and the way the engine runs. But thought maybe? The timing is set at 10 degrees with the spout disconnected. Running on the third Ignition module as the first new one I put on was defective and my idle got much better after replacing it. Also went for a new coil at the same time. I will try moving the distributor a bit and see what that does. Am going to track down all the grounds just to see. I do wonder if something is expecting output from the air pump that's not there. The vacuum lines are plugged coming from the relays/valves on the right fender that went to the air pump.

 

There are only a few major players that will make the engine not want to run very good or not at all. I did the same as you, and disconnected different things to see what would happen;

The TPS is used mainly to tell the computer when to go into idle strategy mode(voltage less than 1 volt, vehicle speed is near zero) and it's used as a accelerator pump. I think out on the road with the TPS disconnected, the engine would run if you feathered the throttle very gently and got the rpms/speed up.

The engine temp sensor is very important. It won't hardly run with this disconnected. It's one of the main players the computer uses to fuel the engine.

The map sensor is very important. Another major player for engine fueling, it won't run very well without it either.

It will run fine without the oxygen sensor. The only difference you will really see with it is a small increase in fuel usage.

The EGR and it's sensor is another unimportant system if it's disconnected. The computer will retard the timing a little bit when it finds out it's not working, but besides maybe a little pinging it won't affect the engine too much.

But the EGR brings up something I would try. I would take the EGR off and put a block-off plate under it. This can be a simple as a piece of aluminum flashing or a aluminum pop can. The reason I say this, if you have too much EGR, it can affect how the engine runs. If the control system, which is a combination of the computer and vacuum valves, is not hooked up correctly, I am wondering if the EGR is flying open after the engine is revved and is choking the engine. Just something else to try.

Also make sure you wiring to the dist is ok. There are some shielded wires in that harness. There are small voltage signals that run from the dist to the computer to tell the computer engine timing info and rpm info. These signals are easily interfered with by the spark plug system, so they shielded a few of the wires. Make sure the shield is there and is not touching and shorting out any bare wires.

I know on these early trucks there was a important smaller ground wire that comes off the battery negative terminal, goes through a single wire plug which likes to corrode near the battery, and then goes into the harness and is the main ground for the EEC. Check this also.

 

Appreciate that info.Yes all the sensors have been changed out and recently I went back and tested them all based on procedures I found here or on other sites. The former ford fuelinjection.com site was a lot of help in learning about the system. Glad its been preserved (oldfuelinjection.packrad.net) as it also was a lot of help when I updated the alternator.

On the EGR... Yesterday I started thinking along the same lines as you. Got out my vac pump and the diaphragm works as it should. Then started the engine and opened and closed it and noted that it seems to do what its supposed to and there is a change in the idle when I open it manually with the engine idling. There is vacuum coming from the control valve when the engine is above idle and releases at idle. The EGR could be leaking some so I will try a blocking plate as suggested to rule that out.

I agree another close inspection of the distributor and its wiring could be a good thing to review. I'll also look at the grounds. The one at the battery has been redone but I should look more at the others.

Thanks and I'm going to also look at the computer I took off for leaky capacitors. A long shot but I may have 2 bad units but the truck performs identically no matter which one is connected.

Anyway please keep the ideas coming!

 

I wish there was some way to actually look at what's going on in the cylinder. Because really, no matter if it has the most fancy fuel injection system ever made, or the simplest carb, the same thing is needed in the combustion chamber, the proper amount of fuel and the proper spark at the proper time.

For instance in my ranger's case, if I could have determined easily that I had a weak spark, I could have concentrated in that area. I am not sure if one of those old scopes would have picked it up. With the right person and the right machine they may have been able to spot the problem but then you still have to figure out why it had a weak spark.

I also think some of the smart guys can look at the injector pulse width and determine if the engine is being over fueled or under fueled.

That's a major problem with the older EECIV Fords though, most mechanics hate them. There is no way to get streaming data from them without using a break-out box and manually measuring what's coming from or going to the sensors and actuators.

 

I know what you mean, With the older plain old carb systems diagnostics mostly could be done mostly from experience or by swapping a couple of components. If it wouldn't start or run correctly, It was either fuel or spark or mechanical like a slipped timing chain. The OBD1 has been a little bit of help figuring out problems along the way and I got it down to the 2 codes I now pull (used to have about 5). I know why I get the Air Pump code and suspect that the Knock sensor code is either the sensor itself or wiring. But I cant find anything that says the computer will be upset enough to affect drive ability other then to throw a code for either error. I was a pretty good mechanic in the 70s and early 80s just as feedback carbs started to show up. I remember hating them and deciding it was time that cars became a hobby for me rather than a profession because I no longer enjoyed digging through webs of hoses that cars were starting to come with and didn't want to go to school again to try and keep up with all that mess.

 

If you want to try it, do the engine running self test again. During what they call the "goose test" rev the engine to above 2000 rpm and while you are doing this peck on the engine somewhere with a small hammer. I bet the code 25 will go away. During this goose test they set the timing high and then look for some pinging from the knock sensor. But for whatever reason sometimes it doesn't pick anything up and and will give you the code 25. This is what the guy in my book said to do to make the code go away.

by the way thanks for that link above. Since Ford made him take that site down it's been all over the internet and I had lost it.

 

I went through driveability issues with my 85 5.0L EFI AOD, no CAT and air pump deleted. I chased all this stuff for a couple of years, off and on. Some interesting things I found were corroded ground points and wires broken at terminal connections. Also, a bad solenoid that controlled the vacuum to my EGR.

The fix to my woes was to remove the ECM/PCM..whatever it's called...to check for the leaky capacitors. I didn't find any obvious problems, so I buttoned it all back up until I could afford a new computer. My truck has ran perfect ever since! Obviously, this was an issue with electrical contact. I'm assuming a ground issue.

 

I agree, a lot of unnecessary misery and expense can be avoided by ensuring bulletproof ground points and connections. Don't just "look" at them, by the time corrosion is visible then that connection has failed altogether or will soon enough. But marginal or high resistance will cause all kinds of problems long before that. Take a wrench and disconnect them, starting with the battery. Clean them up with a file or grinder down to bare shiny metal. Replace 30 year old starter and battery cables.

Any electrolytic capacitor, say 20 years or older should always be replaced regardless. Visual inspection is useless for finding the good ones. Surprised they've lasted this long.

 

OBD 1 also offers a Cylinder Balance Test that may tell you something... to initiate it, I believe you do something like floor the gas pedal after it has given you the KOER codes but do some homework and look it up, I don't do enough of those to remember how to do them.

 

Thats part of the regular KOER test? I'll look into that in case it's something I have not done. Have done both The Key off and on tests. Thanks.

I retested the EGR sensor yesterday while checking grounds and noticed the one on the truck seemed to not be as responsive as the one I have from another truck. Replacing it didn't make a difference as far as the problem I am chasing and I had no codes related to the sensor.

The only open ground I was able to find was the HEGO ground at Pin 49 of the ECU. I ran a separate wire but noticed no difference.

One thing I noticed, The problem seems to show only in Park/Neutral. I tried yesterday putting it in drive and holding at 1500 rpm. I don't get the drop on rpm and rough running when its in gear. Seems to only be in neutral. If that is the case I guess I can live with it but still would like to figure out why that's happening.

 

Well an update...
Testing and retesting sensors. Finding nothing out of spec. Trying to decide on going to a carburetor and dumping the EFI or ordering a re-manufactured ECU. I got out the vacuum pump and ohm meter and retested the MAP. It seemed to be roughly in range according to the information I could find on testing it. The ECU would pass an occasional code related to it being out of range but again only once and awhile when ran the KOEO test. So I replaced it. Problem solved. Thanks for all the responses.