1992 Ram 150 3.9L v6, 3 speed auto trans: Engine bogs down under load, very little power, slows down going up hills. During warm idle in neutral the vacuum is 15 inches. After opening throttle valve vacuum climbs to 19 inches. However in drive the vacuum is 13 inches at idle and drops to 5 inches when the throttle is opened. Is this a motor problem or a transmission problem?

I read on another thread on this site where someone's truck would bog down for a while and suddenly clear up and run good until the next episode. Their description of the way their truck ran when it was acting up matches what my truck is doing. My truck just runs that way all of the time. It will cruise o.k. on level roads. Yesterday I was doing 60 and floorboarded it. I went about 1/10 mile like that and the speed never increased. It did downshift and stay in second until I lifted my foot. It is as if the PCM will not allow the engine to have the gas that my foot pedal is calling for. The engine does backfire into the intake manifold under load and the problem is worse when the engine is cold.

I have put numerous bottles of Sea Foam, Gumout, STP, etc. in the tank. Primarily I use 100% petroleum fuel. I am trying to locate a fuel gage now to check pressure but I don't think that is the issue. I may have a major filter failure and the injectors could be staying stopped up.

I have replaced o2, manifold temp sens., coolant temp sens., throttle position sens., exhaust system including cat., timing chain & sprkts., oil pump drive shaft & bushing, plugs, wires, cap and rotor. The only diag. code is 45 - open or short in overdrive solenoid circuit. The truck doesn't have an overdrive transmission, but could it still be a transmission problem? Can the transmission be seizing or trying to go into two gears at once or something and bogging the motor down?

I'm open to suggestions.

 

No trans problem I know of with those symptoms. Is it throttle body injection? It sounds like the injectors are not spraying properly. Look down into the throttle body and give it gas. You should see a little fuel cone at the bottom of each injector and no streams or empty spots in the cone. If you have a face safety shield wear it or at least glasses just in case you get a backfire.

 

Ouch! Can you actually see the cones? I wouldn't have thought they were that close to the throttle body. I do have a face shield and I will try this as soon as I get home this afternoon.

 

Yes. The injectors sit even with the top of the throttle body. The spray cones are only inches down inside the throttle body. There are 2. Side by side.

 

Ah - I think we are talking about two different systems here. My motor has six injectors, three down each side of the motor, and they are no where near the throttle body. The throttle body has no gas lines to it at all. However, the fuel injectors have been high on my list of suspects. I once removed them, sprayed carb cleaner in them, put new o-rings on them and reinstalled them. It didn't help.

 

I still suspect an injector or 2. You have the (MPFI) Multi Port Fuel Injection system. That is why I asked if it was (TBI) Throttle Body Injection. I was hoping for TBI because they are easier to check. The only way to truly test your injectors is to remove them and take them to an injector shop.

Take a length of rubber hose. Put one end in your ear and the other on the injectors one at a time with the engine running to see if they are working at all. You should hear a clicking as they fire.

You can unplug each injectors electrical connecter one at a time. If it doesn't have an impact on engine performance I would suspect that injector.

Have you checked the timing? Have you replaced all of those parts due to this problem?

 

Just got to work and saw your post. We are on the same track. I removed the injectors yesterday evening and hope to find someone today with the equipment to clean and test them. I unplugged them one at a time and three of them (1,2 & 6) made a more significant difference than the other three and one of them did not seem to make any difference at all. The timing was in spec. The parts that have been replaced were either a stab at correcting the problem or due to something that I detected while trying to correct it. The dist drive shaft and bushing were replaced after I saw that there was about 3/8" slop in the rotor position. When I checked for slack in the timing chain I saw that the crankshaft could turn about 20 degrees without the cam shaft turning. The exhaust system was rusted and burned out. The cat rattled when you shook it. etc. The only guesses were the throttle position sensor and the o2 sensor. I took it to a dodge dealer once and they looked it over, replaced one injector, charged me $275 and gave it back to me in the same shape it was in when I carried it to them. So I could have almost paid for six new injectors for that price if I had done it myself. Basically, you can guess for less. If I knew someone really good with the DBII test equipment I would let them have a stab at it but I haven't found anyone with the right equipment in the area where I live. Each time that I replaced something major like the timing chain or the dist shaft and bushing I thought that when I cranked it back up the problem would be gone. I still hold on to the hope of that happening. The work that I have done so far needed to be done but I will be so darned happy when I finally fix whatever is causing it to run this way. I own and/or have owned five dodge products, four of them v6's, and the others have run like a top.

 

I have a V8 with fuel injectors and with much trouble shooting I finally found my engine didn't have power because 2 injectors were plugged with what looked like mud. I changed the rotor, cap, wires, plugs and nothing helped. The 2 cylinders that had plugged injectors were always fouling the plugs (two much oil and no gas). Thought it was bad rings or valves but the plugs would not fire because they were not getting gas. Cleaned the injectors and runs like a champ but now need to replace the transmission.

 

Pickerbush18 - did it run so well that you burned up the trans? I hope I don't do the same, but with a v6 that probably won't happen. Here's the scoop. I had removed the injectors and replaced the orings sometime back without it making any difference. But last week I did some surfing and found one site where it was recommended that you use a flashlight and look into the top end of the injectors. I added the step of using a magnifying glass. What I saw shocked me. The inlet end contains a small filter basket maybe 3/16" in diameter and about 1/2" deep. The filters were full of hardened deposits. Nothing would come out of them and without using the light and glass I missed seeing the problem the first time. I used a board with six holes drilled in it to hold the injectors upright and sprayed carb cleaner in the tops. After 5 minutes or so I inverted them and bumped them against a wood surface covered with a cloth. A little bit of stuff came out. I sprayed them again and let them sit for a while. This time a little more stuff came out. I straightened a paper clip and carefully used the end to dislodge the stuff from the bottom and sides of each filter, resprayed them and let them sit for a couple of hours. Then I sprayed them full of Sea Foam Deep Creep and let them sit again. The next morning I rigged a 9v battery and push button to energize the injectors one at a time and inverted them holding them lightly in a vice and sprayed carb cleaner through the discharge end to back flush them. This is a three handed job so you need a friend to push the button while you hold the straw in place in the end of the injector with one hand and operate the aerosol can with the other. You could do this well by yourself if you had a foot pedal. Be careful not to get the carb cleaner in your eyes and don't let the electrical circuit arc. Bottom line - my truck is finally running well after two frustrating years of chasing my tail. I plan to purchase a ultrasonic jewelry cleaner and clean them further sometime in the future. It is amazing how much difference it made. I bought the truck 4 years ago and having read that the 3.9L had 180 hp I wondered where it went because the engine was always weak and it went downhill after that. Now I see the 180 hp. It is truly amazing how much difference it makes.

 

The first tank of gas got 19.2 mpg - the best I've ever recorded. I was getting around 13 before cleaning the injectors.