Ok here's the problem I have a 1988 F-250 HD 5.8 w/C-6 trans 3.55 gears with 120,000 miles the truck seems to run great just doesnt seem to have the power on the hills that I think it should ?Maybe it shouldnt have any more power than it does?On the highway with the cruise on i can loose 10-15 mph on the hills pulling my boat (which only wieghs about 2000lbs) and the hills arent that big.
Is this all just the way truck was set up from Ford.

 

I have an 88 F-150 5.8 with a c6 and It pulls my boat (3000 lbs) like it's not even there.

Good places to start checking are Timing, fuel filter, and Compression.

When was the last time you replaced rotor/cap/wires/plugs?

When you loose the 15 mph, do you hear the motor accelerate to try to compensate? It's normal for the truck to loose MPH when going up a hill if it does not accelelrate to compensate.

There are two types of cruise control systems.

Some are "speed based". They Communicate with the speedometer or speed sensor on the truck and accelerate or decelerate the motor in order to maintain that speed.

Other systems are just "pedal holders" which hold the accelerator at a given position. If the terrain changes, the speed of the vehicle will change.

I'm not sure which system our trucks have, as mine didn't work when I bought the truck. It was added to the "Extra parts" pile a long time ago.

 

Let's see the plugs,wires,fuelfilter,cap,rotor are all new or fairly new,I replaced timing chain &gears under advise of a mechanic did not change any thing except more new parts.The cruise control I'm not sure of I don't feel the difference in motor accellerating on the hills just loss of power/speed,which is also the case if I'm holding the pedal myself.Did a compression check last wknd.
lowest was 145 highest was 180 that was dry test,wet test ranged from 170-200 psi.I've gotten mixed reviews some say everythings fine some say it needs rings I don't know whos right!!! This motor doesn't seem to miss a baet to listen to it ,got great oil pressure (new bearings & high output oil pump) Maybe computer problem,but no codes.Thanks for any help or advise!!!

 

How about the fuel pressure?
Air cleaner?
Also could the exhaust be plugged? (cataletic converter)

Just some random thoughts....
Jim

 

I had the fuel injectors & fuel rails profesionally done (cleaned @ ford dealer)and the catalytic converter was emptied out before I got the truck. They said fuel pressure was also fine.Thanks again...

 

Your compression numbers don't look good to me. I believe that you are only supposed to have a 15% deviation from your highest compression number which = you have possibly an unhealthy cylinder/s

 

Make sure your timing is right. I bumped mine up to 15 degrees and that made a noticable difference. Mine is a 90 with the 5.8.

 

What does the truck do with out the boat? Do you have oversize tires? I can feel the accelerator pedal move, when on cruise, as the cruise control compensates for different loads on the motor. Is your cruise giving the truck more gas to pull the hill? The f250 weighs around 5000LB and wind resistance of a barn you must put the gas to it to pull a hill. You might want to post on the performance, engines --forum about the compression reading if you do give each cylinder reading not just the range. I would not recommend this but you should be able to hit the speed limiter with your truck. I have a 460 xcab 4X4 with 167000 miles and the truck limits at 107 mph, not that I would really go that fast.

 

I agree with Mustang42. That, together with the number of miles on the engine and the difference between the wet and dry compression tests indicates that your engine is starting to get tired.

However, even with a fresh 351, an F250 or F350 with 351 and 3.55 gears is not going to win any races uphill, especially if it's a 4x4 Super- or CrewCab longbed, as these trucks are heavy (mine weighs ~6500 lbs in day to day unloaded driving) and the 351 just doesn't have the ***** to pull a high gear ratio like 3.55:1.

Aside from doing a performance rebuild on the engine and a better exhaust, or replacing the truck with one that has a big block or a diesel, the easiest and most direct route (but not necessarily cheap) to increasing pulling power is to swap out the 3.55 gears for 4.10's or 4.56's.

I went from 3.55's to 4.56's in my '92 F350 4x4 CrewCab with 351 & C6 and 33" tires and experienced a significant increase in hillclimbing/towing power and stoplight acceleration. Before the switch the truck was a real dog and got bad mileage unless the road was totally flat and the truck unloaded.

Since changing the gears, it's still not what I was used to with the 454 engine and 4.10 geared truck I had before this one, but it is certainly a much needed improvement and is acceptable for what I do with it. It does pull better, doesn't lose nearly as much speed on the hills as it used to, and it actually gets better gas mileage now than it did before too, which is real nice.

The only drawback I have is that, without an overdrive trans, I don't get to cruise at fast speeds on the freeway like I could before, but that's ok with me. I don't drive all that fast anyways and I just take the back roads instead of the crazy California freeway whenever I can.

Lose the 3.55 gears and you'll get some pullin' power out of that truck.

 

WOW!! Let's see I'm running stock 16"tires,the timing is set to factory but maybe I'll bump that to 15 btdc and try that .As far as changing the gear ratio to 4:10 or 4:56's sounds expensive? Do you have to do front and rear diffs.?Is this a job that I could do myself or is there specific shop,tranny shop,or someone else?This would calm things down a bit from the almost 3000 rpm @65mph ya think.By the sounds of things maybe this truck's not really as under powered as I'm thinking just wrong gearing?If anyone knows how much this would cost and best place to find the new gears I would appreciate it.My last truck was the all powerfull F-350 dually w/460 in it,maybe my expectations were to high with F-250 4x4 5.8 THANKS ALOT!! I'm glad I found this forum.

 

Your rpm's will increase if you swap in the 4:10 or 56 gears. If you've never done gear changes before, better let someone else do it. Things need to be set up right.

 

With the 4.56 gears and 33 in tires, you would be turning a higher rpm at 65mph than you are turning now. Yes you must change front and rear. Here is a link that will let you compare tire, ratio, mph and rpm. http://www.tyres1.com/tech_calcs.html

 

If your truck actually has 3.55 gears in it, you're not taching 3000 rpm's at 65 mph with stock tires. You should be about 2600 rpm with a C6/3.55 axle @ 65mph with 31.5" dia tires (235/85-16's or 265/75-16's). 4.10's will bring you up to about 3000 rpm @ 65 mph with the stock tires. I'm at about 3200 rpms @ 65 mph with C6/4.56 and 33" tires. I try to keep the speeds at 60mph or less to save gas and don't do alot of fast California freeway driving.

Yep, you have to change the gears in both axles if the truck is 4wd. I got mine done at a shop specializing in axle/gear/driveline work. Their labor rates were as expected for California and thier parts prices were very competitive with what I see advertised on the internet for name brand gears and differential (I used Dana Spicer front gears, Precision Gear rears, and had a Powertrax LockRight put in the rear too). Total came to $1650 + tax and it was worth every penny to me. I could have used cheaper gears sets, but I wanted the best quality available and didn't mind paying for it. The locking differential accounted for $325 of that total price.

If you use the gear ratio/tire size/rpm calculator, add 200 rpms for torque converter slip in the C6.

I probably shouldn't have mentioned the 4.56 gears in my original post. If you have stock tires, 4.10 is the best ratio. If your tires are oversize, then a lower (numerically higher) ratio would be needed, depending on tire size, which is why I have 4.56's in my truck.