Bucking under load - driving me insane

[trader007]

1999 Ford Ranger XLT
4.0L
4x4
Extended Cab


Problem?

Truck hesitates under load. Miss fires under load/low rpm. sometimes, especially when cold i have to hold the pedal to the floor while it bucks and misses just to get it up to 50mph. after the engine fully warms up it usually stops missing and i can literally power brake the back tires until they smoke. some days though, it just never comes around and it runs like crap.

Solutions?

"Everything". I kid you not, I am a car guy, have a good scan tool, pressure guages, voltmeters... and have been chasing this slowly growing problem for 2 years now. About 4 months ago I just started throwing parts at it.

New parts- (not all related to problem, I know, but listing anyway)

coil pack/plugs/wires
fuel filter
fuel pump
o2 sensros (all three, although they are 80k old now)
transmission (fully rebuilt)
Lower intake/upper intake gaskets
air temp sensor
mass air flow sensor
idle control motor
pcv valve
crank sensor
camshaft position sensor
water temp sensor
injector cleaner (which never made a damn bit of difference)
64lbs of fuel pressure (perfect)
no vacuum leaks
only codes that come up are "system too lean" which is on about every millennium era ford.
took apart and cleaned every connector i could find, with deoxit cleaner and then coated with dielectric grease for water protection.

Ok, so without getting into a whole lot of background, let me lay out some history that I am 99% certain on.

The problem is in the ECU.

I have taken a couple pictures. You can see where I added new caps. They are doing some sort of power filtering, and when I replaced them it made a HUGE difference. in fact, for almost 2 weeks the truck ran like a wet dream. thought i fixed it, but it slowly went back to missing and bucking under load.

Now, the caps are still fine. I even replaced them again and no change.

Does anyone have any sort of knowledge as to what normally goes wrong with these, besides the caps? Its a bitch to work on, the whole thing is covered in dried silicone. I do know this ecm directly controls the voltage that drives the fuel injectors and the ignition coil.. and from the way it runs it does seem like a spark issue (i will get immediate full power and then back to missing all the time... its very instant and very random)

My soldering is a lot better than it looks too. I am tired and a little frustrated, if you can imagine.





And I will tell you, my biggest problem here is identifying the components. I can test most stuff, but without knowing what it is to begin with I don't know what to test. If I had a datasheet for this computer it would be done by now

 

[swynx]

one thing you didnt change out was the fuel pressure regulator, it messed my truck up in a similiar manner for awhile. also why not go to the junkyard and get a different ecu?

what engine? 4.0?

 

[trader007]

Thanks for the reply. Edited OP to show my truck specs

No pressure regulator because they cost $100, and I have tested my fuel pressure a few times now- its always above 60psi

no ecu swap! pats system! one key! which means first I need the stealership to program two new keys ($150) then i have to find a good used ecu ($150) then i have to have the stealership program the new ecu to work in my truck or it wont even start ($250)

the damn truck is barely worth $1k... I cant justify putting half the value into the computer... a used one at that, which will likely fail the same way after the next 100k miles.

 

[tmcalavy]

Sell it and get an older one that you can work on to your heart's content.

 

[Chris_North]

I'm really impressed man. I didn't think there were too many people left out there that made repairs with a soldering iron...

Just an idea, not sure how possible it is, but could you maybe get an ECU its key from a junkyard? I don't really know the ins and outs of PATs, but isn't the key a transponder? Does it have to be in the ignition to work? If it does there are a lot of hardware stores that program keys now, maybe they can program a new key to the new ECU but cut it to your old key? Should be looking at around $250 instead then. Like I said I don't know much about the stuff, just thinking aloud.

 

[AgPete139]

This is ridiculous, guys. He's asking about a specific problem, and not asking what other vehicle to buy.

You stated you fixed the Idle Air motor(?)... are you referring to the Idle Air Control Valve? You cleaned it out with brake cleaner liberally? Easy to recheck.

The Mass Air Sensor is the other sensor that is tricky. My other 1997 4.0L did the same thing. It bucked under load, I had to brake + gas at lights to prevent it from stalling, and it would die in the cold. I did the same thing to my current 1997 4.0L (yes, I've had two) when I first started to experience trouble, and it stopped. Give it another solid clean. Do you use a K&N air filter? Being an oil / reusable filter, these have a tendency to put a film over the sensor, causing it to get crap readings when a richer mixture is required (ie: when cold or under load/acceleration).

Does your truck have any mods?

Your vacuum lines have no leaks, but do you think they might be clogged? How many psi vacuum are you getting at idle, and how much at other RPM's?

I wonder if your fuel injectors are clogged. You are getting good pressure at the rail, but what about PAST the rail (the cylinders)? Honestly though, it still sounds electrical to me.



*****************

Slightly unrelated, but I had the most serious issue with my 5.0L Mustang ~5 years ago. The most violent bucking you can imagine. It ended up partially being the Ignition Module (Ford is a must, autoparts aftermarket did not last and had short lives) and the PIP.

What did you do for the coil pack?

Has it occurred to you that it may be an improper ground?


Hopefully ADSM will stop by and contribute his $0.02.

 

[Metalcrack]

Were the caps bad, leaking, burned, physically damaged....essentially why were they replaced? Did you use the same value to replace with?

 

[trader007]

This is ridiculous, guys. He's asking about a specific problem, and not asking what other vehicle to buy.

THANK YOU. I am not buying another truck. This thing only has 249,100 miles on it! I just broke it in!

You stated you fixed the Idle Air motor(?)... are you referring to the Idle Air Control Valve? You cleaned it out with brake cleaner liberally? Easy to recheck.

I replaced the IAC motor AND cleaned the butterfly. No change.

The Mass Air Sensor is the other sensor that is tricky. My other 1997 4.0L did the same thing. It bucked under load, I had to brake + gas at lights to prevent it from stalling, and it would die in the cold. I did the same thing to my current 1997 4.0L (yes, I've had two) when I first started to experience trouble, and it stopped. Give it another solid clean. Do you use a K&N air filter? Being an oil / reusable filter, these have a tendency to put a film over the sensor, causing it to get crap readings when a richer mixture is required (ie: when cold or under load/acceleration).

I replaced the Mass Air Sensor. No change at all. I use paper filters. Cheap and I dont have to clean them, just replace them. I don't know why people use cotton filters

Does your truck have any mods?

No. I like stock because it usually WORKS.

Your vacuum lines have no leaks, but do you think they might be clogged? How many psi vacuum are you getting at idle, and how much at other RPM's?

I don't know about PSI, but its a good strong vacuum.

I wonder if your fuel injectors are clogged. You are getting good pressure at the rail, but what about PAST the rail (the cylinders)? Honestly though, it still sounds electrical to me.

I have been using injector cleaner every oil change for the life of the truck... i don't think they are clogged either.


*****************

Slightly unrelated, but I had the most serious issue with my 5.0L Mustang ~5 years ago. The most violent bucking you can imagine. It ended up partially being the Ignition Module (Ford is a must, autoparts aftermarket did not last and had short lives) and the PIP.

The ignition module is inside the ECM, as far as I know on this truck.


What did you do for the coil pack?

Brand new BWD. no change.

Has it occurred to you that it may be an improper ground?

Yes, and I really don't think it is (I am an electrician by career)

Were the caps bad, leaking, burned, physically damaged....essentially why were they replaced? Did you use the same value to replace with?


The caps LOOKED fine. I had to pull them out and test them with my ESR/Capacitence meter to find they were toast. Well, the one was OK but the larger (16v 47uf i think) was completely dead.

The good news? truck has been running amazing!!!! Those 3 caps you see in my pic are the new LOW-ESR type. I had different ones in there first, and thats what the problem was. For whatever reason the problem didnt go away for a couple of weeks after installing these LOW ESR caps, but I think the computer was just really whacked with those other caps in it. I did try disconnecting the battery overnight, but for some reason it didn't help. I just kept driving it, and every day it got a little better. It seems the new LOW-ESR caps did the trick. Finally, after 18 months and about $1k in parts I finally fixed the problem with $1.54 worth of caps and 20 minutes of labor. And now that I replaced all of those other parts (I think everything except the engine block), this ****in truck is running like a wet dream! LOVE THIS THING!

 

[bmerr98]

Glad you got it figured out! Pretty impressed with the tracking down of the problem and the know how to fix it too. And I am with you on the "break in" period! 200-250k should be enough to get the bugs worked out of most Rangers, and by then most everything has been replaced anyway, so it's the next best thing to a new truck!

You have been repped!

 

[AgPete139]

I'll send a rep, too. Congrats on finding the problem.

I'll keep this in mind for the future.

Kick back with a cold one, Trader.

 

[trader007]

Thanks

I just figured out the LAST problem too! ever since its been running good (a couple weeks now) i notice i still have a dead miss at startup. no big deal, it would go away after a minute of running, but I wanted to figure out what it was.

knowing i also have a slow coolant leak that wasnt going anywhere external, i suspected the water (once hot and pressurized) was squirting into a cylinder.

In an attempt to just see if anything changed, i threw in a can of stop leak into the radiator. I have been losing about 1/4 gallon every 600 miles or so.... not a terrible leak but it was there...

dumped the stop leak in last night, drove home and let the truck sit overnight. This morning- NO MORE MISS! fired up and ran like a brand new motor instantly. And now there is zero vibration at idle. it purrs like a sewing machine. this is a 99 4.0 OHV motor with 250k miles on it!!!

So basically I need to replace my head gaskets. I think though, because its such a slow leak, i will flush this crap out and try some good head gasket sealer. I have a feeling it will last a long time.

 

[tmcalavy]

After using stop leak I would pull the rad and have it professionally cored and flushed...that schtick is nasty.

 

[trader007]

After using stop leak I would pull the rad and have it professionally cored and flushed...that schtick is nasty.

only if you use too much of it. one can isnt going to harm anything. i have seen entire heater cores plugged up because of this stuff, but thats because people dump 5 cans in

 

[trader007]

Problem back!

the other day (btw, my truck is one rusty piece of shit, oh my god) i was filling up with gas, and when i go to put the cap on it broke apart.

Oh well, new OEM cap was ordered. Problem was during the two days i was driving without a gas cap the truck started running like SHIT again.

got the new cap on, but the engine kept missing and having no power (just like it used to when i started this thread 6 months ago).

re-set the computer by pulling battery cable, but didnt help. maybe its just a coincidence and the computer is just failing again, but it seemed to lose itself the moment the truck with driven without the cap. i know it shouldnt make that big of a difference, but i think with this computer its just barely doing what it should.

ill take it apart and test the caps this weekend. was sure a nice 6 month run of perfect running truck...

 

[trader007]

Pretty unbelievable, but I found the problem. This time the computer was in fact still OK. It was the spark plugs! They were last on my mind since I replaced them 8k miles ago

Autolites, never again. One had two cracks in the ceramic insulator! The others were severely worn. There is no reason for this, the truck was running fine with them until they failed.

I popped in NGK 4177's and instantly, for the first time in over a month, truck runs without miss, hesitation, backfire, bucking... its all gone. It runs absolutely perfect. Just turned 259,000 too.

I had so many problems with the computer in the past I kept thinking it must have finally gave out... but I checked as many components and points as I could and I simply couldn't find anything suspicious... now I know why, because the computer is working fine.