MWO - Project "Ambo" 1991 F350

[MidwestOverlanders]

I had to drive home yesterday to take my mother to a doctors appointment, which granted me a little bit of time with the Ambo. There's definitely some mechanical bugs to work out, but it's been sitting in a barn for the last 4 years and only driven in yearly parades prior to that. There's been some solid shade tree mechanic work going on... more like lets bandage this part to get home and never fix again type of deal.

One thing I noticed while driving up and down hills is that it doesn't like to get over 40 mph and the transmission is constantly shifting up and down and damn near hitting red line. This is the first time driving this large of a truck, so maybe its something that I just have to work with and get used to. I do know that the second trip I turned OD off to see if that would help, but it came back on by itself. Maybe a faulty switch?

The front tires are new, but the back tires are fairly shot with a good amount of dryrot. Looking online, every manufacture wants to put in a commercial line tire. I'd rather go with a good all around AT tire. I specifically have the Mastercraft Courser ATX LT215/85R16E in mind. They have a gross max weight of 2680lb (assuming single wheel), so I figure around 2465lb with a 8% dually differential. They are load range E. Anything that I'm missing here that would warrant a commercial tire over an AT?

 

[pappawheely]

Leave the world of predetermined boxes and off the shelf behind. Just do your homework and run what you think is best for the way you will be using your truck. I'm sure tire rack, etc does not have an ambo category on their tire selector. I've been building custom vehicles for years and have had many problems with parts guys trying to sell me something I don't want or need.

 

[MidwestOverlanders]

Leave the world of predetermined boxes and off the shelf behind. Just do your homework and run what you think is best for the way you will be using your truck. I'm sure tire rack, etc does not have an ambo category on their tire selector. I've been building custom vehicles for years and have had many problems with parts guys trying to sell me something I don't want or need.

Totally agree. Again, that's why I'm doing research plus asking for opinions here. This is my first time owning a dually, so just trying to get some feedback. I got a quote today for $1300 on six new Mastercraft Courser ATX today, so as soon as the my wife's maternity leave is over in August i'll put some new shoes on the pig.

Once the 4x4 swap is done, I'd love to turn it in SRW and run 37x12.5s on it.

 

[tgreening]

Just out of curiousity, when your tranny si doing all that funkiness is your speedo going goofy as well? Mine is a 1992 and there are at least a couple things that can make your tranny do all kinds of weird junk. One is the ABS sensor in the rear end, assuming you have one. Another is the tach sensor on the front of the engine. On my model year at least these both have an affect on tranny operation. It got REALLY weird when that abs sensor went. Shifting like it had a mind of its own about what gear was best at any given time. Up side is neither part was too awful expensive or hard to replace.

Uhmm, is yours a diesel? If not take what I said with a grain of salt because I'm not sure if any of it crosses over.

 

[MidwestOverlanders]

Just out of curiousity, when your tranny si doing all that funkiness is your speedo going goofy as well? Mine is a 1992 and there are at least a couple things that can make your tranny do all kinds of weird junk. One is the ABS sensor in the rear end, assuming you have one. Another is the tach sensor on the front of the engine. On my model year at least these both have an affect on tranny operation. It got REALLY weird when that abs sensor went. Shifting like it had a mind of its own about what gear was best at any given time. Up side is neither part was too awful expensive or hard to replace.

Uhmm, is yours a diesel? If not take what I said with a grain of salt because I'm not sure if any of it crosses over.

Yep, mine is the good ole 7.3 IDI non turbo. I'm not sure if the speedo went goofy or not. The engine was screaming when it would downshift and hit 4K on the tach. I'll look in to those parts. Honestly, this truck is now 25 years old and at least the last 10 years it was only occasionally driven in parades (once or twice a year) and then parked. I think i'll just go through as time and money permits and upgrade most everything on the truck.

Thanks for the feedback!

 

[underdrive]

Yep, mine is the good ole 7.3 IDI non turbo. I'm not sure if the speedo went goofy or not. The engine was screaming when it would downshift and hit 4K on the tach. I'll look in to those parts. Honestly, this truck is now 25 years old and at least the last 10 years it was only occasionally driven in parades (once or twice a year) and then parked. I think i'll just go through as time and money permits and upgrade most everything on the truck.

Thanks for the feedback!

Speedometer won't b goofy on these usually, it's cable driven. The TCM (transmission computer) gets its signal off the same sensor yes, but it's the electronic part of it, so it is possible to have solid speedometer reading and erratic signal to the TCM. The VSS on top of the rear axle is only used for the rear ABS setup (RABS), you can leave it unplugged even and it won't make any difference to the transmission.

The sensor on the engine is for the tach. Yes the E4OD needs it as well. If the tach reads semi-accurate at idle your sensor is good, they drop to zero RPMs at idle when they get wonky.

4k actual engine speed is only possible if downshifting too low and overspeeding the engine. Typically the governor will defuel the pump at 3600 or so free-revving, about 3200 under load. Sure does sound like it's running at mach 3 tho So your tach is off a bit. No big deal, just make sure it actually reads something at idle.

Check the TPS adjustment, you want around 1.1V at idle, IIRC 1.2V is the max the TCM will tolerate - the higher the voltage the later and firmer upshifts and easier downshifts happen when under load.

I think the main issue is that it's an underpowered engine in a overweight vehicle. Turbo will help, but don't expect miracles. Basically you need to always remember that you will never be the first to arrive, but you will pretty much always arrive, as that engine offsets its lack of power with stone-simple reliability.

 

[MidwestOverlanders]

Speedometer won't b goofy on these usually, it's cable driven. The TCM (transmission computer) gets its signal off the same sensor yes, but it's the electronic part of it, so it is possible to have solid speedometer reading and erratic signal to the TCM. The VSS on top of the rear axle is only used for the rear ABS setup (RABS), you can leave it unplugged even and it won't make any difference to the transmission.

The sensor on the engine is for the tach. Yes the E4OD needs it as well. If the tach reads semi-accurate at idle your sensor is good, they drop to zero RPMs at idle when they get wonky.

4k actual engine speed is only possible if downshifting too low and overspeeding the engine. Typically the governor will defuel the pump at 3600 or so free-revving, about 3200 under load. Sure does sound like it's running at mach 3 tho So your tach is off a bit. No big deal, just make sure it actually reads something at idle.

Check the TPS adjustment, you want around 1.1V at idle, IIRC 1.2V is the max the TCM will tolerate - the higher the voltage the later and firmer upshifts and easier downshifts happen when under load.

I think the main issue is that it's an underpowered engine in a overweight vehicle. Turbo will help, but don't expect miracles. Basically you need to always remember that you will never be the first to arrive, but you will pretty much always arrive, as that engine offsets its lack of power with stone-simple reliability.

Thanks for the info! At idle it hovers around the 1K mark, so that makes me feel like the sensors not off. I'm only noticing these downshifts when going up larger southern Indiana hills. I do like to go into the mountains, so I might have to just get used to its higher revs or install an aftermarket tach. I have no need to be speedy in this thing, but I would like it to be able to handle highway/interstates speeds (60/70) where we live. My dad mentioned an engine swap, but I've always wanted a diesel...so there's some allure there to working with this 7.3 idi.

 

[pappawheely]

Come out to Cali and we can swap motors. I have a nice 460 that I will trade ya! The weather is great and it will be an adventure.

 

[MidwestOverlanders]

Come out to Cali and we can swap motors. I have a nice 460 that I will trade ya! The weather is great and it will be an adventure.

Haha, I appreciate the offer, but I think i'll stick with the old oilburner for now I wouldn't be able to afford gas with a 460 in this pig.

 

[tgreening]

Where is the model year split for cable/non cable speedos? Mine is a 1992 and is definitely not cable driven. The vss in the rear end pulls duty a few different ways. Provides info to the abs system. Provides info to the gauge cluster which apparently uses it for the speedo and passes it on in some fashion to the tcm. I'd have to dig back to refresh but I went through all that crap trying to figure out my shifting/speedometer issues last time around. When the sensor went bad the speedo would alternate between just fine and total wack job, the abs light would come on and off (light on crazy speedo. Light off everything fine), and the tranny would shift according to its mood. About 20 minutes of time and somewhere around $20 for the sensor and not a twitch since.

 

[underdrive]

Where is the model year split for cable/non cable speedos? Mine is a 1992 and is definitely not cable driven. The vss in the rear end pulls duty a few different ways. Provides info to the abs system. Provides info to the gauge cluster which apparently uses it for the speedo and passes it on in some fashion to the tcm. I'd have to dig back to refresh but I went through all that crap trying to figure out my shifting/speedometer issues last time around. When the sensor went bad the speedo would alternate between just fine and total wack job, the abs light would come on and off (light on crazy speedo. Light off everything fine), and the tranny would shift according to its mood. About 20 minutes of time and somewhere around $20 for the sensor and not a twitch since.

'91-down are cable drive, '92-up are electronic with the PSOM thing. The PSOM is the speedometer gauge mechanism, it reads the VSS signal off the rear axle and apart from showing you a corresponding vehicle speed it also translates it into a signal the PCM/TCM/ECM and cruise control will understand. Which is exactly the same type of signal the old VSS on the transmission or transfer case was sending them in the '91-down trucks. For '92-up basic failure diagnostics is as follows:

1) if truck loses speedometer reading consistency but ABS still works good, suspect PSOM.
2) if both speedometer and ABS go wonky at the same time, blame the VSS in the rear axle.
3) if speedo and ABS are fine but PCM throws a VSS code, and cruise is so-so at best, suspect the PSOM again.
4) if PCM acts up, but cruise is good, suspect PCM.

For the older cable-drive trucks it goes like so:
1) any ABS issues, check VSS on rear axle.
2) wonky speedometer, cruise works good - speedometer cable or head are questionable.
3) wonky speedometer AND cruise, suspect VSS on transmission or t-case rear output housing.
4) good speedometer but wonky cruise, it's most likely the electric part ofthe transmission/t-case VSS causing that.

 

[tgreening]

'91-down are cable drive, '92-up are electronic with the PSOM thing. The PSOM is the speedometer gauge mechanism, it reads the VSS signal off the rear axle and apart from showing you a corresponding vehicle speed it also translates it into a signal the PCM/TCM/ECM and cruise control will understand. Which is exactly the same type of signal the old VSS on the transmission or transfer case was sending them in the '91-down trucks. For '92-up basic failure diagnostics is as follows:

1) if truck loses speedometer reading consistency but ABS still works good, suspect PSOM.
2) if both speedometer and ABS go wonky at the same time, blame the VSS in the rear axle.
3) if speedo and ABS are fine but PCM throws a VSS code, and cruise is so-so at best, suspect the PSOM again.
4) if PCM acts up, but cruise is good, suspect PCM.

For the older cable-drive trucks it goes like so:
1) any ABS issues, check VSS on rear axle.
2) wonky speedometer, cruise works good - speedometer cable or head are questionable.
3) wonky speedometer AND cruise, suspect VSS on transmission or t-case rear output housing.
4) good speedometer but wonky cruise, it's most likely the electric part ofthe transmission/t-case VSS causing that.

This. Now this right here is the kind of crap that can make or break a forum. I'll have to print this off and put it in Ambos Big Book of Knowledge I'd Otherwise Forget. Thanks a bunch.

 

[underdrive]

Thanks for the info! At idle it hovers around the 1K mark, so that makes me feel like the sensors not off. I'm only noticing these downshifts when going up larger southern Indiana hills. I do like to go into the mountains, so I might have to just get used to its higher revs or install an aftermarket tach. I have no need to be speedy in this thing, but I would like it to be able to handle highway/interstates speeds (60/70) where we live. My dad mentioned an engine swap, but I've always wanted a diesel...so there's some allure there to working with this 7.3 idi.

FYI, the spec for warm idle speed is 650-750 RPMs, cold idle is higher cause if the special solenoid these engines have to b ump up the engine speed to help them run smoother and warm up faster when just fired up, you're looking at 900-1000 RPMs usually. Ours is set at 650 warm and 950 high, the high idle is on a switch and gets turned off pretty much only when truck literally just idles when parked for prolonged periods of time. Yours being an ambo you might also have that feature installed already.

In any case, what gear rations you have in the rear axle? 4.10s with the factory 215/85-16 tires will make the engine run pretty high all the time, going with the slightly larger 235/85-16 helps a bit. Overall 3.55s gears are your typical highway cruiser setup for better fuel economy, 4.10s are great all-around gears, and for heavy hauling you could get 4.56s as well. The '91 user manual book lists both 3.55 and 4.10s listed for your 8250-lbs rear axle, no 4.56s there, but this are the standard issue gears, you truck being special-built can have whatever the locality that originally ordered it wanted installed in it. If you do have 4.56s you are doomed to the slow lane and high engine speeds till you either install significantly larger tires (this will be after your SRW conversion) or change the gears in the axle. Regearing a Sterling axle like yours is a very DIY-friendly job, we've done a few with junkyard-special gearsets even, and neither I nor the better half are professional axle people, just taking it slow and paying attention to things and all is good. I would do axle regear well before the engine swap your dad suggested, for one thing the IDI is a doomsday engine that is very reliable and will run on just about anything that burns, and the other thing is all the wiring is already set up for a diesel and you won't be able to run EFI without switching a bunch of fat long harnesses out. Besides, what are you going to drop in there, no gasoline engine will move this heavy of a truck properly without passing everything but a gas station

 

[underdrive]

This. Now this right here is the kind of crap that can make or break a forum. I'll have to print this off and put it in Ambos Big Book of Knowledge I'd Otherwise Forget. Thanks a bunch.

Oh, no problem, glad to help! But the thing is that one should also look into other more brand-specific type - for example everything I posted could be found on Ford-Trucks or whatever. Don't take me wrong, here we have Korben, Pappa, Seabass, and a few others I can't think of right now, who have been playing or working with these trucks for a while now and know lot about them. But it's very possible for someone to ask a question and not get a timely response simply because the people who can provide one are all busy doing life things. So checking with a more model-specific discussion board is also a good idea, well at least as long as the members there don't behave like douches most of the time, which there are a few such places.

 

[tgreening]

Oh, no problem, glad to help! But the thing is that one should also look into other more brand-specific type - for example everything I posted could be found on Ford-Trucks or whatever. Don't take me wrong, here we have Korben, Pappa, Seabass, and a few others I can't think of right now, who have been playing or working with these trucks for a while now and know lot about them. But it's very possible for someone to ask a question and not get a timely response simply because the people who can provide one are all busy doing life things. So checking with a more model-specific discussion board is also a good idea, well at least as long as the members there don't behave like douches most of the time, which there are a few such places.

Oh yeah. I'm active over there as well. I'll generally post the same issues to both sites. Here it's more a matter of adding stuff to the build thread and keeping folks up to date than digging deep for know-how on the idi. FTE is where I go after the real info, not that some folks here don't have it, but as you said, over there is idi specific whereas here is more van-general.