*Fixed, look on last post*


Gentlemen. A pleasure to be a part of the community. I recently purchased a 1993 F150 with the 4.9L straight six. It's 2 wheel drive, about 186,000 miles, 2.73 rear gear with a 5 speed, long bed. It's currently on 33's which are kind of annoying and loud but give a good appearance. I picked it up a couple weeks ago for $1800. Not sure if it's a good deal or not since it does have some rust. A/C blows cold and heat is nice and toasty. Can't really complain too much.



I am, however, having a persistent issue I can not track down. There is a slight stumble under throttle tip-in. I have been reading the forums for a few weeks and have seen where many have fixed a similar issue by putting a small washer into the EGR tube. I did that today and, while it did clean up the power delivery a bit (it revs much smoother now), it didn't fix the tip-in hesitation. I have taken a video of the problem. Any advice would be appreciated.


I would like to get this worked out and get the truck ready to tow my racecar a bit. If you take a look at my youtube channel I have been building an early 90's Mazda Miata over the past 2 years. It was built for autocross. I won my class in my region this year and now am wanting to move onto some light track racing. The car can be driven on the street just fine and I trust it would make it there and back but it is not a pleasant place to be for hours at a time. So getting this truck into condition to tow the car would be the best for me.

 

Use the search function and you will find many past threads on this kind of issue. Likely suspects include vacuum leak/s, sticky/faulty IAC, and faulty TPS. Have you checked for codes?

Vacuum leaks are very common, especially with the factory vinyl lines.

 

I didn't want a larger wall of text in my first post.

I checked for vacuum leaks. With a can of carb cleaner. I guess I could try to pressurize the system and use a cigar to go further.

I have cleaned the TPS and IAC pins and used dielectric grease upon reassembly.

I have not pulled codes but I have no current CEL. I will go pull them off the ECM and see what is stored.

Most of the issues I see people talk about are bucking and stumbling throughout the power band. Mine is with very small throttle inputs and very noticeable when cold.

Is there any keyword I should use for my search? I usually try and search as much as I can before making a post.

 

Pulled codes.

522 - Neutral/Drive switch (NDS) Doesn't really matter, can start the car with clutch out.

556 - Electrical circuit of fuel pump (assuming the rear tank pump is out)

then after single CEL flash

512 (repeated) - Keep alive memory (KAM) fault. Says to check KAM fuse, if ok then module faulty. Not sure what in the world this means.


Then went and did a dynamic test

225 - Knock Sensor (I'm not pinging so I'm not very concerned with this unless it has authority to pull timing)

226 - EEC IV/EDIS module pulse (No idea what this means)

 

Use keyword "stumble" or "hesitation."

Seems you already found some threads specific to the 4.9 and the EGR causing issues and tried to mitigate that issue.

The codes reported don't seem related to me. KAM is Keep Alive Memory, if I am correct this is used by the pcm to store real world sensor values and adjust operations instead of using default factory values. Could,? maybe.? be the problem.? Sounds like part of the PCM has failed, assuming it isn't just a blown fuse. Not my area of expertise?.?. I would seek out more info on that issue...

You can try cleaning the IAC valve itself, and reinstalling.

I would still suspect a vacuum leak. Could be a leaking line, (some of which are in the cab for the HVAC system), intake gaskets, brake booster, among other things and these can be a pain to trace. Do you have any symptoms under load, AC cut out going up steep hills?

You could also have dead spot in the TPS that isn't throwing a fault, dirty fuel injectors, minor ignition fault, dirty air filter, coked valves...

If you have the coin and time, doing a full tune up and replacing all the vacuum lines would help to establish a base line and can't hurt anything... as long you don't break anything in the process...

 

Does it have a MAF? A sensor in the air intake plumbing, after the filter but before the throttle body. I left my Explorer's MAss Air Flow sensor disconnected after some wrenching and it had a similar symptoms. It could be dirty too.

 

Per the original post, 1993 F150....no MAF.

 

Anytime I've had this issue, Sea Foam treatment helped. It's cheaper than replacing parts, and easy to do. I also agree with cleaning the IAC valve...I'd also spray the entire TB internals and externals with carb and TB cleaner. I know you didn't pull a 0171 code, but when I do the work above, I also get the PCV valve. The only time I've had a situation like you're having that couldn't be fixed with thorough cleaning, it was a carb with a known dead spot that was caused by design.

 

Do you know where I could find more information on this? I feel like I could figure it out reading a wiring diagram but, I don't have a factory service manual to reference. Is there a link to an FSM on the forums that I overlooked? I didn't see it in the stickys.

I love the free stuff. I'll give this a shot today after work.

I sprayed carb cleaner on every hose I could find. Every gasket post throttle body. I didn't hear any audible change in RPM. I have no other symptoms of a vacuum leak.

Honestly, the TPS is something I suspect. I was reading that sometimes when people replace them they are not calibrated right, rather to say the casting process is not 100% and the tang has moved position giving a false reading. People get past this by elongating the holes in the mounting tabs. I'll get a voltmeter out and start reading resistance and/or voltage and see if that could be an issue. I had something similar happen on my racecar when I went to a speed density setup and a BMW TPS for the Megasquirt.

 

I've never been a fan of SeaFoam. I just always thought it as a placebo but, as this problem seems to still exist after all my troubleshooting I may have to come over to the dark side. I think a good cleaning of the TB and IAC is a good next step.





Thanks for the input everyone. I usually try not to reach out to the community but as a last resort. Since the truck is pretty new to me and my first domestic vehicle I am getting to know the systems and how they work. This is much different than the Japanese stuff I usually find myself wrenching on.

 

KAM info
https://www.ford-trucks.com/forums/3...pwr-fault.html

You can test the TPS with a voltmeter to see if there are any dead spots. An analog meter seems to be better for this as you may not catch dead spots with a digital meter.

Be very careful about cleaning the throttle body. Your throttle body should have a special coating to prevent buildup and to keep the blades from sticking in the bores, and the cleaner could remove the coating. I did a little searching and didn't see a conclusive answer on what is safe to use.?.? Maybe someone will chime in...

 

Removing the TB is the best answer to clean it. That way, you can check for a damaged gasket and the 300's seem prone to that.

Just use a soft paper towel to clean the bores and blades. Could also use mild washing detergent.

As said, DON'T use carb cleaner!

 

Thanks for letting me know about the throttle body. I hope someone in the past hasn't got at it with some carb cleaner and a wire brush.

 

I didn't think about it earlier but I think there is a Ford TSB on the efi 4.9 having throttle body gasket failures...

 

https://www.ford-trucks.com/forums/1...dy-gasket.html