Alright here's the skinny, I recently picked up a 98 ram 1500 5.9l and shortly thereafter I started losing heat and getting a po300 on cylinders 1 and 8. I replaced the t-stat (195),ect sensor(because of increased overcooling), plugs, wires, cap, rotor, ignition coil, researched and completed any pertaining tsb's, tested and cleaned all injectors, replaced pre-cat 02 sensor, cleaned all hot and ground connections, tested fuel pressure(was 46-54 psi),checked for vac leaks, fuses/relays. After that it's still overcooling and misfiring as a result. I tried to burp coolant system after i heard bubbling noises coming from the core but not positive i got it all out. So I'm not sure if I got a bad t-stat or ect sensor out of the box or is it possible this thing was altered from stock to take a 180 t-stat? The truck was from Jacksonville,NC(is in MI now) and wondering if it was tuned to better suit the warmer weather. The temp on the gauge never passes 170-180 no matter how long it runs. Also the fan clutch checked out ok but fan never stops running.

 

Moved to the tech section.

What thermostat did you get? If it isn't getting up to the temp the stat is rated for, more'n likely a bad stat.

Did you check the plenum?

 

i'd find it hard to believe that the engine would be too cool without tossing a p1281 at you.. it seems it's quick on the trigger with that one..

the engine closes loop somewhere around 140*, and pulls sensor data to operate- the weather or climate isn't as much a factor with a computer controlled system..

the misfires are likely not a result of being too cool.. even if it were too cool, the engine would simply toss more fuel at it in effort to more positively ignite the charge.. the misfires sound like another issue all together..

did you route the wires per the TSB? (check faq section)
is your plenum gasket blown? (sticky thread at top of thread board)
what kind of plugs did you use? not platinum or iridium are they?

 

the plugs are the right ones definitely, it's not throwing any codes, the plenum appears to be fine as i don't see any of the signs for blown gasket nor are there any vac leaks. tried three different brands of 195 t-stats and the plug wire tsb was the first thing i tried for the misfire. funny thing is you cant even notice a misfire until i get up to at least 40-50 mph and when i ease up to level out and coast is when it starts and if i take it out of od it's way less noticeable. tranny can't b an issue on that note as i have a jasper reman that was put in less than two weeks ago.

 

Yeah, what you describe is classic signs of a miss. Right about 45MPH, trans goes into O/D, and TCC locks.... if you have a miss, THAT is where it will be most noticeable. Can feel like the truck is trying to shake itself apart.

I wonder if either the gauge in the dash, or the sending unit is lying..... would be an interesting check to plug in a scanner, with the engine fully warmed, and see what temp the PCM thinks it is....... not to mention the fact that the gauges are notoriously inaccurate to begin with........

Done a compression check on those two cylinders?

 

Was the cat checked? It may be clogged. And was the crank sensor uninstalled before removing old motor, and reinstalled after the new motor was put in?

 

This doesnt help, but Just so you know. I have the overcooling problem to.. 00 dodge ram 1500, replaced the thermostat which was a 195 with another 195 and it stays at 170... Unless Dodge has a huge line of bad tstats.. I dunno.. I gave up and left it be.. (Its not misfiring though..)

 

zman: crank sensor was replaced and i was charged for it on the bill. in fact to be sure i checked, it's new. however, my iat sensor wiring connector was a little charred on the black wire terminal but voltage checked ok and the ohms on sensor were in spec for the temp. and as far as the cat, no, so i'm going out now and pulling the o2 sensor to see if anything changes, and now that i think of it all my plugs looked pretty except #8. also, since timing can't b taken care of the straightforward way on these models, is it quite possible my fuel sync needs reset? I used to own a straight six f150 and it had this similar issue on timing but that was easily fixable by a slight tweaking of the cap. Post cat sensors don't cause this do they? because i also noticed whoever put one in last kind of crimped the sensor tip.

 

umm... fan clutch locked up, always running.. always cooling down really damn good.. ? Just pointing out the obvious in your comments.. take it off and see how quick it warms up once it gets to 195ish shut down.. and you can put it back on if need be.. that is what I would do... but that's just the shade tree in me.

 

It may or may not be part of the problem, but I'd definitely have the fuel sync reset either way.