Hey everyone,

I have a 1987 Dodge Ram D100 with the 3.7l 6 cylinder and the 4 speed (3 sp with overdrive) tranny. My issue is this. The truck is fine driving in town, but on the highway, it doesn't seem to want to get up to speed. When I shift into overdrive at whatever speed, the truck refuses to accelerate, or even hold the speed I'm going sometimes. It seems like if I pump the gas I can make it accelerate slowly, or sometimes if I hold it to the floor, it will slowly start to accelerate; I often have to downshift to third to hold speed while going up hills. It seems like it's a little bit better in the summer when it's warm out, but still not great. The only known issue I have with the truck is a tick every once in a while, but that goes away. I also smell gas occasionally around the truck, but I have yet to find a gas leak.

I know this kind of rambles on, but any help is appreciated.

 

My 84 has the same problem and I have a 318 in it. The only problem is that it's old. Try giving it a little tune up and cleaning the intakes, but in my experience nothings going to fix that. You just have to accept you're gonna have to constantly shift gears on the highway.

 

It could be as simple as a fuel or air filter, or catalytic converter plugged up. Could be a failing fuel pump, or leaky fuel line. Maybe bad plugs, or wires. If fuel injection, the injectors could be plugged. You'll need to do some checking. If you don't know how, take it to a shop that does. Just tell them to find out whats wrong,and the estimate to fix, but not fix it until they get your OK. I wouldn't go to a dealer, find a local shop you trust, and feel good about. Ask around.
They should run an electronic diagnosis on the ignition system, check the timing, a fuel pump pressure test, and a compression test.
If you can do some of the work, change the filters, andplugs, and see if the plug wires look bad. Try running some fuel injector cleaner through it. If that doesn't work, disconnect the exhaust if possible, but disturbing it may mean you'll need to replace it. If it runs good with the exhaust off, it's the cat.
Good luck!

 

I should have been a little more specific with my last post, sorry. I put a new fuel filter, new air filter, new plugs, and new wires on the truck, and there wasn't much of a difference. I have ran injector cleaner through it, but that did little if anything; I was thinking of trying seafoam next. I also tried carb cleaner spray to clean down the throat of the carb, which also didn't change anything. The exhaust did fall off of the truck once too, and it really wasn't any better. I was going to look into the timing, I just haven't gotten to it yet. I thought maybe someone had the exact same problem and could help me past the troubleshooting. Another symptom the truck has; it will start good when it is cold (well, good for an older truck), but when it's warm, it starts quite a bit harder. If this were a motorcycle I'd guess that the valves are out of adjustment, but my research said that they aren't adjustable on this motor; although it looks like the motor was replaced at one time, so I'm not sure what to think (there is a metal tag on the oil pan from a shop, and the exhaust mounts don't look stock; although they did a good job with them).

As you can probably tell, I've been fighting with this problem for a while (almost two years, 1 of which this truck was my daily driver), but I just found this forum, so I figured I'd ask. As a little background, I've been fixing my own vehicles since I started driving, and my dad raced circle track for years, so we have plenty of experience and tools to fix stuff; we're just looking for ideas.

 

OK, if it has a single coil, try a different one. Abad coil won't produce as much spark hot aswhen cold.
Another possibility is the pick up coil in the distributer, same reason as coil.
Also, advanced timing will cause that, but you should hear spark knock like crazy.
Did you check the compression yet?
Do you have any idea how many miles are on the motor?

 

Hey, just an update. I fixed a vacuum line, and that got rid of most of the gas smell, but I sometimes still smell gas when I get out of the truck. The timing was at about 17*, specs say 12*. I set it back to 12 just for good measure. I also poured two cans of seafoam into the gas, just to see if it helped. It appeared to do a little bit, the truck can go 60 most of the time now, but I'm sure it's still not right. I'm sure it's a fuel related problem, it feels like when I push the gas more than 1/2 way, it has no effect at all, like its not getting any more gas at WOT than 1/2 way. It also seems like maybe there's a flat spot when accelerating; when I take off or shift, the vehicle truck pulls pretty good, but almost immediately hits a flat spot, and doesn't start to pick up again until it sounds like its over-revving (about 15 mph in first, 25 in 2nd), and obviously I shift then. I replaced the air filter again, but haven't driven it since putting the new one in, so I'll see tomorrow if it helps; the old one was pretty dirty.

 

Is it carb'ed or fuel injection? There is some better fuel injector cleaner which requires running cleaner right through the supply line, so it runs on cleaner, not gas. Can't remember the name.
Or the carb might need rebuilt.
Are the linkages/cables OK? Almost sounds like the linkage is binding and not giving you full throttle.

 

Or the tps.

 

My truck has the 1bbl carb., I don't believe that there is any kind of computer equipment or sensors on the truck. I had the same problems today, so nothing I did fixed it. I think I'll check the linkages tomorrow, that's a good idea that I never thought of. If it gets to the point where the carb. needs to be rebuilt I think I'll just deal with it; I got in an accident with my car the other day so the truck is again my daily driver, at least for now.

Thanks for the help guys.

 

Keep us updated.