I am working on a 88 Dodge Ram 250, it has a TBI 318 with an automatic transmission, for a fellow firefigher. It is setting a code 13 for the map sensor, vacumn leak. He has already replaced the map sensor and replaced the computwe with a junkyard computer. He does not have the orginal computer, so I dont know if its the same part number. I have replaced a few vaummn lines I found that were cracked. I checked the wires at connector for the map sensor. I have the five volt reference and the ground is good. I do have voltage on the other wire. I used a vaummn pump at the sensor and jumped the wires, you can see the voltage drop as vacummn is applied. I checked the wires in the loom, and found a splice that was corroded. I replaced the splice and disconnected the computer. Reconnected and the code still comes back, The only thing I have not done is checked the resistance in the wires. Has any one run into this problem or have any ideas as to where I should check from here?

 

Do you have vacuum to the MAP from its source? Does the voltage from the MAP change as it should when the RPMs change? Get a can of carb cleaner and spray it around any place a vacuum leak may occur while the engine is running. Any change in RPM indicates a vacuum leak.

 

Yes I have vacummn to the sensor. I have not checked to see if it changes with the RPM, but doing that is similar to the test I performed with the vacummn guage. I have sprayed cleaner and could not find any other leaks. I did forget to mention it is hard to when first starting. Apparently after talking to the owner this has been an on going problem for about five years, the code 13 and the hard starting and has been taken to several shops. Thanks for the input and have a good evening.

 

The MAP is an input sensor for the computer and is ignored during starting. It has absolutely nothing to do with the starting process so I would look elsewhere. Our early computers have been known to set codes that point to certain systems that have no problems because there is a problem elsewhere. I have found that drivability symptoms are a better diagnostic tool. We now know it starts hard but how does it drive and idle? Is there a lack of power when accelerating? Does it cut out when stopping or decelerating? More info is needed.

One of the first things I now check on a TBI system is the spray pattern of the injectors. Remove the air cleaner and look down the throat of the throttle body while the engine is running. Each injector should have a fine cone of fuel at its base that has no gaps or streams and each cone should reach the sides of the throat. Low ambient light and a flashlight show the cones better.

Have you checked the timing lately?

 

I tried commenting on this yesterday, but the computer gave me crap. I've ran with a 22 year old MAP sensor, a brand new MAP sensor, and no MAP sensor. The truck ran fine all three ways. Changing it got rid of code 13, but nothing else. I have a bunch of other codes, but like SEAL said, I have no symptoms, so there isn't anything to fix, for me at least.

 

Sorry I have not responded. I have been dealing with sick kids. Thanks for the replys. When you first start it you have to give it gas until it warms up. Driving down the road it drives pretty good. Every now and then whe you are stop, with it in gear, it shuts off. I will check the injector spray and voltage while it is running today. Once again thanks for all the help.

 

I would also suspect the EGR valve/system. I like to pull the EGR valve and blank off the manifold opening with a home made plate and go for a test drive to see if the problem clears up. You should know immediately and the only cost is a new EGR gasket.