90 F-250 5.8 ZF5-speed 3.55

The truck doesn't seem like it has much power past about 2700 RPMs, and maybe I'm just used to driving an automatic and not used to the stick yet (or maybe not used to EFI), but I thought that when you stomp on the gas, the RPMs are supposed to go way up. Mine will in 1-3, but won't in 4 and 5... In 4/5, the RPM's go up slowly, if at all, and that's going from 1/4 throttle to foot-on-the-floor.

The reason I'm asking is because I was doing some reading about a bad TPS, and thought that maybe that was my problem, but I know that someone on here will know for sure and can tell me the correct answer on how to fix this......

 

I may be off here but automatic transmissions usually downshift when you floor it. When you're in too high of a gear the engine's gona bog down. Feel free to correct me if I'm going in a totally different direction.

 

In an automatic, when you stomp on it and the rpm's go way up, it's because the transmission automatically kicked down into the next lower gear... Try downshifting your 5speed to the next lower gear when you want to pass somebody and your rpm's will go way up . One other note, a 351 with a 3.55 axle ratio in a heavy 3/4-ton truck isn't a real hot performer. The truck is heavy, the gear ratio is high, and the engine, well it's just not real powerful considering all the weight it has to move. In my F350 CrewCab 4x4 with 351, I had to change to 4.56 gears to give it some much-needed ooomph on the hills and when loaded/towing.

 

LOL Faroffthetrack, you're not far off at all! We were both thinkin' the same thing at the same time (didn't see your response while I was writing mine).

 

LOL nice one

 

I probably just phrased it wrong. What I meant was that, in my old truck (76 Chevy 1/2ton 350 3-speed auto.), you could stomp on the gas, and you could feel it pushing the seat back against you, without shifting. This one doesn't do that. My main concern is the RPMs not going up at all in 4th and 5th..... Yeah, I know this isn't a great speed truck, but I think the rpms should go up a considerable amount. The main point is, in 4th and 5th, on flat ground, the truck doesn't accelerate. At all. If I want to go faster, then I have to put it in 3rd, and at 2300 in 4th, I can just imagine what that would be like in 3rd........

btw, I wish this thing had a 460 and better gears, but oh well. I bought it for the fuel economy (damn gas) and possibly for towing occasionally, and even that has turned out to bite me in the butt so far (10 mpg), not to mention the enormous amount of money we've spent on it.

 

4th and 5th gear are not going to have hardly any pull like a Turbo 350 did in your Chevy.

Your 3 speed Auto is going to rap out a lot faster than the 5 speed in your Ford will. Your also a little heavier than your old Chevy.

Steve

 

True, but I still thought that the RPMs should go up since I'm going from 1/4 to full throttle. 1/4, 1/2, none, it doesn't matter. It won't go above the RPM's that it was at when I shifted into that gear.

 

Well I don't remember the hp and torque rating for our trucks but its not the most impressive numbers to be pulling aprox. 5600#(Truck Weight) in the higher gears.

I think your truck is running ok its just not a runner. My 92 is not either in your same situation.

Steve

 

You likely don't have enough gearing to get it up into the higher rpms. What size tire are you running?

 

I guess the question I don't see yet is, what speed are you doing when you floor it in 4th or 5th? If you're doing, say, 30 in 4th, you aren't going to get much acceleration (you don't just want your RPMs to go up--that would be bad). If you're doing maybe 60 in 4th, then you should see SOME acceleration, but it's no racecar.

Think about it this way, too: if you're going 65 in 5th gear at X RPM (don't know what it is on your truck, maybe 1800?), then if you were doing 2X RPM in 5th gear, you would be doing 130--not real likely with a stock 351 from 1990 in a ~6000lb truck.

Jason

 

ok. First, I've got 33" tires on it. That might end up being one of the problems.....

When I hit the accelerator, I'm usually doing around 45-50, and the RPM's might go up 2-300, going 1/4 to full throttle.

Here's another thing I can't figure out. I noticed this problem more when I first began driving the truck. Now that I've been driving it for a while, I don't know if I just got used to it or it actually did loosen up (truck hadn't been driven for a year, taken care of in about 3-5 years), but it seems to be doing better at this, but still not too great (and I think it could be better)

I'll definitely agree, the truck is underpowered. It certainly doesn't like hills (a problem in my area ). And yes, the lower gears would help immensely, but I don't really have the money right now to be putting in new gears or different axles. I was going for fuel economy with the 351 over the 460, and that ended up biting me in the a$$. Oh well, we all have to learn from our mistakes.

P.S. If I wanted something that drove like a racecar (and had the money), I'd trade the truck in tomorrow and get the 03 Mustang GT I drove today. That was a fun ride........

 

Have you seen the new '05 Mustang? I'm in love with it :P .

At any rate, yeah your 33" tires, 351 engine, 3.55 gears, and heavy truck all add up to one thing: Gutless, especially on hills or with a trailer behind. I went through the same thing. I got the 351 for 'fuel economy' too and got bit in the rear end as well.... I was dead set against the 460, since I had just got rid of a 454 dually that put me in the poor house whenever I tried to drive it any distance. I wanted a diesel but couldn't afford one with low miles and didn't want a high mileage truck. So,, what I ended up with was a great truck with no *****.

Honestly, the best thing you could do for it, if you intend to keep it, is save your pennys and do the gear change. I bit the bullet, to the tune of $1800 (gears in both axles, plus a locker in the rear), but it was well worth it. Now I can drive like normal cars and not slow everyone down going up every hill. The truck finally has pep! I'm quite pleased with the gear change. Sure, it's still no big block or diesel, but at least it goes like a stout truck should.

Why on earth Ford saw fit to put such small underpowered engines and such high gear ratios in these monstrous trucks, I really have no idea, but the person who decided that oughtta be forced to drive a Yugo the rest of their life!!

Good luck with the truck!

 

Hey SoCalDesertRider,

What gears did you go with?

Thanks,
Steve

 

Wojo, I went with 4.56's. They are LOW with that size tire (33"), and may not be for everyone, but I do like them alot.

4.10's would be a more conservative choice if you don't have overdrive, which a C6 doesn't have. I have the C6. The ideal ratio would have been 4.30, but that ratio was not available for my 10.25" rear axle, so I chose to err on the low side with 4.56's rather than on the high side with 4.10's, figuring that if it ended up being too low for me, I could go to 35" tires and that would put me back to the same effective ratio as 33's with 4.10's.

The truck does go highway speeds with this low 4.56 ratio and no overdrive, it just sucks alot of gas doing it, so I keep the speed down to 60mph or less and get descent mileage out of it.

I had a truck before with 33's and 4.10's with a 350 engine and no overdrive in the trans and it was a heavy truck too. The gearing in that truck was pretty good for all-around use, towing, offroading and freeway driving. I would recommend 4.10's with 33's and no overdrive if you like to keep up with most traffic on the freeway and still get descent mileage doing it.

I don't mind driving slow, but would still like to have an overdrive gear sometimes. That aside, the 4.56's are certainly an improvement over the 3.55's in all other kinds of driving. My mileage when loaded or driving in hilly areas went UP with the lower gears, since I don't spend so much time with my right foot to the floor anymore .