[mikenolanak]

i have a 1997 ram 1500 with a 3.9
when runnung truck it will only reach about 45 miles an hour
seems to backfire, and the exhaust is getting red hot it seems to have a missfire at an idle but the scantools cant pick it up.
im assuming a vacuum leak but can not locate one
i also cant find to proper fuel pressure rating - i get 45psi but i think thats too low and could be causing a lean condition also??
please help!

 

[hemimech]

If your truck has high mileage say 125K+ the timing chain may have jumped a tooth or two. This would delay fuel delivery (fuel injectors are driven by pickup coil in the distributor) and retard spark therefore stifling power.

 

[hemimech]

Fuel pressure spec. for 1997 3.9L 5.2L 5.9L is 49.2 psi +/_ 5 psi. So it needs to be between 44.2 & 54.2 psi.

 

[sony224422]

clogged cat.

 

[sony224422]

get under the truck when its cold in the morning and tap on it.. listen for any rattles. if you hear them, its bad and clogged up. i had the same symptoms. i thought my truck couldn't tow my smaller 4500 lb boat.. ended up being my cat was clogged and it couldn't expel the exhaust.

 

[moe7404]

moe in wichita ks
my test for a cloged cat is, if the plugs look like they have been the ext man, then you have a cloged cat

 

[dizzyD]

Been there with lostr power, removing the clogged cat was my fix

 

[threetwos]

Either that or most likely a plugged fuel filter. Has the filter ever been changed? When you depress the throttle in at idle in neutral, does it labor to rev? If so it might be the exhaust,(Cat). If it revs clean in neutral but not under load,(driving), it's probably the fuel line delivery,(filter). Have you placed a fuel pressure gauge on it?