Engine Performance problem
1985 Dodge Ram V8 Two Wheel Drive Automatic 155000 miles
My truck runs good at low rpm, starts good and idles smooth. When I take it up to highway speed it starts to stall as though fuel starved it also does this when I kick it into passing gear. When I let up on the fuel it recovers most of the time, but the problem is worsening and happening with less and less fuel feed applied. I have changed the fuel filter and pump, it still does it as soon as it is warmed up. Truck also runs cooler than normal and has an exhaust leak coming from the crossover tube right side. It is a 318 2V w/AIR. Can anyone give me any ideas? Exhaust problem maybe? Or control module, possible distributor problem? Any help from some experience would be appreciated.
When you cheked the fuel pump pressure, was it normal (possible regulator problem)? Also, the exhaust shouldn't be causing this problem. Also, have you tried replacing the t-stat to fix the engine temp problem? If it is reading cold enough, the computer may be adjusting the fuel mixture for colder conditions causing a problem.
March, 12, 2009 AT 10:12 PM
This truck is pretty much old school. I replaced the fuel pump (easy-mechanical) and I rebuilt the carburetor
(Holley 2280) I also replaced the ignition control module.
All this caused the truck to improve greatly in drivability
and response, however, as soon as I get to interstate speed it falls on it's face just like turning the key off and as soon as I let up on the feed it catches again only now it starts doing it at lower and lower load conditions until it stalls. Let it set a few minutes and it starts and go's until it starts acting up again. Oh yes I did replace the T-stat with an OEM one. My next step will be to replace the distributor which is the vaccume advance type with a single pickup. Suggestions are welcome cause this thing is giving me more of a headache than I thought an old school 318 could (LOL)
March, 13, 2009 AT 9:44 AM
The only thing left is the fuel pump. I know you replaced it, but I'm wondering if the cam lobe is worn thus causing the pump not to produce enough. If you think of it, at slow speeds, there isn't as much demanded of the fuel pump. At high speeds, more is needed.
Also, I wonder if the float is set properly. When you rebuilt it, did you have the right measurements for float drop? Maybe the carb is running dry because the float is set too high and shutting off the gas?
I would double check that and perform a volume test on the fuel pump.
Let me know what you find.
PS: You are sure there are no vacuum leaks, correct?
March, 13, 2009 AT 7:48 PM
Well the idea about the possible problem with the fuel pump seemed like a sound possibility. After all the truck has 155,000 miles on it and a worn cam lobe would not be surprising. I don't have a fuel pressure gauge so I got an external electric pump (4 to 7 psi) and frame mounted it next to the tank. I mounted it as a booster to the mechanical pump. This did improve power and now instead of falling flat under load it tries to die off but the pump wont let it so it jerks (hard surges) at speeds over 60 or under loads such as uphill climbs. Unlike before it doesn't stall out completely, and recovers when the load is taken off. No miss, no backfire, revs well sitting still. I am starting to think the catalytic converter is clogged, but I still haven't changed the distributor because it just doesn't seem to have all the symptoms of a bad pickup assembly, I can tell it is advancing because it will scoot when its cold until it reaches normal operating temp. Gas millage is worse than ever. Could it be the cat?
March, 13, 2009 AT 11:19 PM
A plugged converter will cause poor performance and poor mileage. I was also checking for fuel pressure and the electric pump should do the job. However, I recommend eliminating the mechanical pump. It could cause problems if both are working.
As far as the mechanical pump, I found that if you remove the timing chain cover, attached behind the cam sprocket, is a replaceable cam eccentric that runs the fuel pump. That is good news. If it is bad, the cam doesn't need replaced. Here is a picture:
Check the converter, and try only the electric fuel pump. Let me know what you find.