I have a 1989 F250 with a 460 and a 5 speed that for some reason has a sticker that says it was made in 1994. I assume it's a 1994 motor that was swapped in sometime. I'm not sure about the trans although the guy that changed my clutch said it was a hodgepodge of different year parts.

Anyway, the truck stutters sometimes when I'm driving right when the tack hits 1000 rpms. The tack needle bounces up and down and the truck bucks real bad. I can power through it by pressing on the gas but it bucks all the way up to about 2000-3000 rpms. It seems to smooth out the higher it gets but you can still feel it and it seems like it lacks power. Sometimes it only does it a few times then accelerates mostly normally with some small little hiccups that you can barely feel. If I ease off the gas instead and lightly apply pressure, I can slowly increase rpms till I shift again with no bucking but the going is slow.

It does not do it when the truck is in neutral or in first gear, only when driving. It seems worse with a load in the bed. It has done this since I bought the truck about 2 years ago. It only did it in 5th at first but after I got the clutch changed it started doing it in 2nd-5th.

I replaced the front tank fuel pump assembly last month along with a new fuel filter. The rear tank pump is dead. New plugs, wires, dist cab, rotor, and coil about 2000 miles ago. Replaced a bad EVP sensor with a new one last week. Flushed the radiator and block last week and running about 50/50 coolant mix. There are currently no codes during the key on engine off and key on engine on tests. I checked all the vacuum hoses and electrical connectors, they all appear to be in good working order with no issues. I did a fuel pressure test and all results were within specs in the Haynes manual. I did a few regulator tests too and they were also ok. I've checked the TPS, the EVP sensor, the coil resistance, and a few other random sensors.

I am going to pull the plugs and check the wires tomorrow. I would also like to check the timing. Is there anything else I should check? Would trying to drive around with the fuel pressure gauge on be worth the trouble? Compression check and EGR valve test too? I assume the EGR valve is working as I have not had any codes.
Thanks

 

When it bucks what color is the exhaust?
Have you pulled the vacuum line off the top of Fuel Pressure Regulator (FPR) and turned on the key with a cold engine and see if fuel squirts out of the nipple on top of the FPR.
If you see any fuel at all it is bad.

Let us know what you find.

 

I haven't been able to see any exhaust change although I haven't been looking. I'll start keeping an eye out for it.

I just pulled the vacuum hose off the FPR and no gas came out after a few on/off cycles.

I reset the codes yesterday and drove it around, making it buck. I pulled the codes this morning after checking the FPR and I am getting a code 34 from the continuous memory. From what I'm reading at Fuel Injection Technical Library this leads me to believe that the EGR valve is not staying closed all the time? Is this correct? I'll try and find a vacuum gauge to test the EGR valve.

So if the EGR valve is not staying closed when it should either by opening too soon or leaking, this would lean the air/fuel mixture out too much and cause these issues, correct?

 

If the EGR valve is not closed the idle will be very bad or the engine will die. You will also have a lack of WOT performance.
The EGR valve should only open at mid throttle with a warm engine at high way speed.

You chack to see if that is your problem by unscrewing the large EGR tube, drop a coin in it to block the flow and screw it back on lightly, not enough to ruin the seat. Then take it for a ride.

 

Because the tach is bouncing, I' say the "bucking" is an electronic rather than an air/fuel related problem.

I'd start checking all of the grounds for the ECM (computer) AND remove the computer and give it a visual check.
Click here and read this:A9x ECM's (and same years ECM's) Failures Due to Age
That'll give you what to look for. It isn't the answer for every symptom/problem but, given the fact that the tach is bouncing, it sounds like there's an intermittant grounding circuit.

Oh, and Bill, I got my sh** together on this thread.......sorry for the other day.


Just my take,

Bob

 

I couldn't get a quarter or nickel to fit in the tube to seal the EGR valve off. I did find a vacuum pump and ran some tests on the EGR valve. I put vacuum on the EGR and it held fine. I also tested the vacuum coming from the solenoid and it did what the Haynes manual said it would. It stays at around 0-1 in. Hg and then starts to head toward 8-10 before falling down towards 3-5 in. around 3500 rpms. This is in neutral.

@bob
Man, you sure love that write up lol. I seen it posted in response to a lot of threads. I'll go pull the ECM now and see what we got. I've checked a lot of the wires and grounds in the engine bay, is there anything I should be looking for? Where are the grounds for the ECM? And it does throw error codes, it just didn't have any when I scanned yesterday. It has code 34 now.

 

So I pulled the ECM and it's not the same as what's in your pictures. I did pull it apart and visually inspect for bad caps and components. Everything appeared to be fine.

 

Yes, I do infact like that write up.

Too many folks discount the fact that these "computers" can fail, and never bother to take the time to remove it and visually check for an OBVIOUS problem.
If you looked under the hood and saw a corroded/failing wiring/connector, wouldn't you repair it ????

As far as where are the grounds for the ECM, I'll tell you a little story I've just "lived".

Some 8-10 years ago, just after I purchased my (used) truck, I wanted a factory installed tachometer. Easy enough, went to the boneyard, found a good donor cluster and installed the donor tach in my cluster. Yes there was a pin(s) in my cluster that had to be moved between "A" connector over to "B" connector. Simple enough....right.......
Likewise, when I purchased my truck it had the infamous "EGR stumble".
I had taken my truck to several shops and they had an assortment of band-aid fixes that they proposed to me. I found and did the EGR restrictor "band-aid" fix and every two years I had to un-do it in order to pass Cailifonia Emissions testing.
Then I came upon "that write up" and read where the symptoms of a failing (due to age) ECM's capacitors could cause the "EGR stumble".
Of course I opened up my ECM and found that 2 out of 3 capacitors were failing.
I replaced ALL of the capacitors in my EEC and it still stumbled but not as bad as the pre-capacitor replacement.
Fast foward present.........I still had a stumble even though I did the capacitor(s) replacement in my EEC. So, as of last weekend, I spent some quality time with my truck trying to find the source of the remaining stumble.
After all, NONE of our trucks were driven off of the showroom floor with a stumble problem........hence the search was on.

As found out with the "quality time" I spent with my truck , there was a looped ground wire missing in the "A" connector that plugs into that section of the cluster where the "Factory Tach" is. Additionally, in that conector is a gound wire for the ECM.

So, by following the schematic in my Haynes manual, I realized that the ECM was using the tach ground signal as it's ground........that meant that the ECM was turning on and off as fast as the tach signal.
To further verify that I had an "electronic" stumble, I removed the vacuum hose off of the EGR valve and the stumble was still present.
Now understand that the ECM operates at a certain speed.......
The fuel injectors operate at a variable speed..............
I'm thinking that the injectors pulse rate was being corrupted by a harmonic of the ECM powering on and off.....because my ECM was using was the tach signal (which is a pulsing ground) as a ground.
Once I did that little "ground loop correction" in the connector, the "electronic stumble" disappeared AND upon driving, my transmission started shifting smoother and I no longer had a "harsh reverse" engagement when backing up that I'd had for 10 years.

That's a long winded story , but, I'm just trying to help others by applying what knowledge I've learned from the past, given that "like conditions and symptoms" are present.

Sorry for the

Just my take, nothing else,

Bob

 

Your first post you said,"I'm not sure about the trans although the guy that changed my clutch said it was a hodgepodge of different year parts.

Then you might want to check and see if the ECM you have is correct for your truck. No ???

Bob

 

Bob,
The ECM (PCM) does not use the tach grounds (G100 & G201) for a ground.
The ECM (PCM) uses G101 & G104 for its grounds.
Sounds like you were missing a body ground.

 

In my instrument cluster connector(s) some of the wiring pinouts were wrong and that necessatated the ECM to use the tach signal AS it's ground.

I can (hopefully) with the Haynes manual, find what circuit(s) I changed, but nonetheless, my ECM is now grounded (as required) and is not using the tach signal as a ground........causing the electrical stumble I was experiencing.
It may not be the ground that the wiring diagrams specify, but it is a good solid ground conection now.

I don't know how to cross between your GXXX numbers and the Haynes manual (they refer to them as ground h, or ground g, etc) schematic I was using, but, once again, when I changed some of the wiring to match the pinout in the haynes manual the electronic stumble disappeared.

And I will add this.
The wiring harnesses were messed with (yes both were) prior to my very first removal of the cluster way back when. I think it was for a fancy schmancy alarm/theft system the PO had installed.
Notably, the wire from the inertia switch that goes to the cluster at conector "A" or "B" (can't remember which) was/is missing.

Just sayin', that's my story

Bob

 

Hahaha that write up is posted on another ford forum. Anyway, back to MY issues...

Ok, so I got the numbers from the ECM and it's for a 1989 f250 7.5L with a manual trans. I think. The code is "8SH" which in not on the Fuel Injection Technical Library site. I tried E4LB-14A459-B which is stamped in the plastic on the back but that came back as a 84 Lincoln ECM. I tried E8TF-12A650-BL1B and that came back as a 89-91 F250 ECM.

However, the engine in there is a 1994 engine. I can see the date nice and clear on the manufacturer sticker on the side. What I believe should be in there is a F4TF-12A650-AKA as that would match the year of the engine.

Looking through the truck, I keep finding connectors not connected to anything, wires just taped together or dead ending into nothing, and stuff just generally not connected. I found a battery terminal hookup clamp spliced into a bundle of wires that are just hanging there by the negative battery terminal. I already have a negative clamp going to ground...why...why is this one there? What is it for? Should I ground it?

This got a lot more complicated. I'll spend some quality time with the Haynes manual and schematics. Can anybody point me to a good site to get wiring diagrams for a 89 and 94 F250 so I can compare? I like the tach signal is ground thing. That works for me. Let's hope it's that.

Edit: Oh hey Bob, did you have those issues at idle or when you weren't in gear? When I'm freely revving the engine in neutral everything sounds fine. It sounds extra healthy until you drive it then the random issues start popping up.

 

I would think that they just changed engines and used the 1989 wiring and computer.
It would not be very smart to put a 1994 wiring and computer in a 1989 truck unless there were changing it over to a MASS system. If you have a 1989 computer in it that is not what they did.

So if the computer is bad you need a computer from a truck around 1989 that has the same transmission and engine size that you have now.

The Neg ground cable needs to go to the block and there should also be a 10GA wire going to the BODY and and another smaller black ground wire with a green stripe going to the computer from the NEG ground post of the battery.

A 1994 and a 1989 trucks have a much different wiring system, ignition system and PCM computer.

I take it you just want the wiring for the EEC Computer for the 1989 and the PCM Computer wiring for the 1994.

I will post below the 1989 part with the computer grounds and the 1994. But I dough that they will help you very much.

The 1989 should be close to the 1988 so this is the 1988:


A 1994 would be close to this 1992 diagram below:


/

 

The "G" numbers are the standard letters and numbers used by Ford and in all of its EVTM manuals. I do not use after market wiring diagrams and do not have any Haynes manuals so I do not know about their ground numbers. The Hayes and other manuals are just bits and parts of the Ford manuals from over a number of years. I have also read that they have a lot of wrong information and errors in them from posts on this site.
Ford manuals are for one year truck only and cover it in detail. Yes even the Ford manuals have some errors in them and sometimes I have to go to the large fold out diagram to see whats going on. I have even seen errors in the large fold out diagrams.
Most on here will get and use the Ford EVTM for their year for wiring as they do not cost much if they have a big problem. So that is why I reference the ground letters and numbers from the EVTM manuals.

 

Gotcha' on the manuals Bill.

So, I got the Haynes manual out and the "ground" loop I did by passed the the ground for the inertia light indicator ground which was missing as I previously posted.
Since my "A" connector was physically missing that ground wire, it left an open to body ground that the EEC has to use for smooth voltage ie. not a pulsing tach ground.
Also, after re-pinning the "A" connector and prior to installing the "ground loop" several of my guages weren't working correctly........they were missing a "body" ground.
Long story short is, the missing "pin" in connector "A" is REQUIRED (it completes the body ground circuit within the cluster) for the EEC to be grounded as a "body ground".
I could have used a "pin" without a wire in that connector location and achieved the same end result.

And another thought to consider is, an "electronic stumble" and rough transmission shifts can be caused by poor/intermittant connections at the "A" cluster connector.
Who would haved thunk that !!!!
That thought may be another "tool" to use to help diagnose the source of a "stumble" and/or rough transmission shifting problems for others !!!!

Sorry for the thread hijack !!!!

Bob