Hi, I have an '88 Ram, 318 TB.
When the truck starts, it runs perfect, idle is smooth. I have a fixed vacuum gauge, and it sits at about 17 cold, by the time its warm its right up at 20. Now here is the problem:

When the truck is driving, idling, whatever, if I put my foot down very lightly on the has. Lets say im sitting in the drive, and I put my foot down enough to bring it up to about 1000-1200 rpm's, then the revs will start to go up and down and become unstable. Its very strange, and it goes away when I put my foot down harder, but it just cant hold a steady rev. I pretty confident that it is not a vacuum related issue. O2, water temp, air temp sensors are all new. MAP and TPS are tested and appear good. Plugs are new and gapped, new rotar, cap and plug leads. Hall effect switch is clean. Any ideas would be very helpful. Thanks.

JAcob

 

Sounds like a TPS problem to me. What tests did you run on the TPS to determine it was OK?

 

hi Seal, I thought it seemed like a TPS as well, it meets all of the criteria. I have been dealing with this issue for a week or so, and last week I swapped out a spare TPS i had and it didn't solve anything. Then I got a code saying TPS voltage too high or low, so I swapped it back out. When I swapped it, the sensor actually broke in my hand, I thought for sure I had it solved. Alas nothing. Just as it was. I checked the sensor based on the manual, took voltage reading throughout its travel, everything seemed to check out. There were no "dead" spots either.

I dont think it could be the circuit itself, it has the correct voltage as well.... im pretty stumped here....

 

Alright, so here is an update.... I thought that my issue seemed like a TPS, and SEAL was able to second that.... and even though I had tested mine, I swallowed the cost and replaced it. It turns out, it did help. I went back to the old one with the volt meter, and noticed that when the throttle was at what seemed to be the bad spot, the needle would kinda twitch, but not die out completely, which I think is why I didn't notice it the first time, it was ever so small. The only reason why I noticed it the second time was because I had the new part to compare it with.

Now for my new problem: ugggg

I am having an issue with the truck not wanting to start when it is cold/sitting overnight. Even with the block heater plugged in all night. It is only when the engine is cold, and it will start a little, sputter, die. Retry several times, by this time the engine is flooded and it blows some smoke until the fuel clears. After 10 second, it runs ever so smooth. I have read other posts of people with a similar problem, but not seen any solutions. ALL sensors are now less than a year old. All new ignition, with exception of coil and condenser. Any ideas pleas let me know.... it seems to be getting slowly worse every day..... once its going, it drives very well, I dont think its weak fuel pump since it runs great even under high demand. Thanks

 

Have you replaced both water temp sensors or just one? If just one, which one? Have you checked the injector spray pattern when it is cold?

Look down in the throat of the throttle body to check the injector spray pattern. There should be a fine cone of atomized fuel at the bottom of each injector that reaches the sides of the throttle body with no gaps or streams. Low ambient light and a flashlight helps to show off the fuel cones easier.

 

I have replaced both of the water temp sensors, we as well as they air temp sensor. I have checked the injectors while its running and it looks perfect. Now that I know for sure I have an issue somewhere, I will watch them tomorrow when its cold and get my wife to start it up. Im curious to see if there is a delay in fuel getting to the TB, or if its an electrical issue.

 

Is the fuel pump coming on briefly when you first turn on the key? Are you turning on the key for a few seconds before you try to start it?

 

Just as habit, i always leave the key on while I buckle up and such, just to give the fuel a chance, I do it for any car. I didn't do a full pressure test, but I removed the fuel line and put it into a jar, and ran the pump, and there is a very good flow of fuel, I dont think it is the pump itself, unless there fuel is leaking back into the tank, or there is air getting in somewhere. I will check it next time I cold start it, and if there is a delay in fuel, I will know... if there is fuel, but a delay in start, I know its the electrical.

 

Ok, new update. I went out this morning. It was 8 degrees Celsius..... I popped the hood, and looked down the TB.... i got my wife to start the truck. I got her to do it so that she turned the key right away, without waiting for the system to pressure up. Either way, the second she turned it over there was a beautiful flow of fuel, and it fired right up, couldn't believe it. Talk about the woman's touch!

It may have been just luck, but the only thing I did yesterday was blow back trough the return line to see if it was blocked. It was very hard to blow through, and at first I thought it was blocked, and then I could tell there was a very small amount of flow..... is this normal? How much air should I be able to put through it? (with my mouth). When I pinch the return line while the truck is running, it stalls out.... but maybe its a partial block? I dont know how this would effect things....

 

The fuel pressure regulator maintains 14.5 psi. You can not get anywhere near this pressure with your mouth so blowing thru the line tells you nothing. The only way to tell if the return line is plugged is with a pressure test. If the supply line pressure is above 14.5 the return line MAY be blocked or the regulator is bad. To tell for sure you must remove the return line and direct it into a container. If the pressure goes back down to 14.5 where it should be the fuel return line is blocked.