Started running rich

HI, thanks for visiting 2CarPros.

Sometimes there will be one 02 sensor in the crossover pipe then one behind the converter.

I would look into the no communication with ECM, without codes you're just guessing. IF all the wires between obd 2 port and ECM show continuity and the powers and grounds are present it most likely is a bad ECM. It's rare but if all those check out then that's the issue I would start with.

That's what I'm thinking too. I checked the power and ground, a mechanic check the continuity on the signal wires and said they were good. He suggested a new ecm. And you're right, without the code I'm just shooting in the dark.

I ordered a new ECM today and will have it Monday. I'll update with the results.

By the way, do you know if a 1996 E350 with 7.5l could only have one O2 sensor? 1996 was a funny year. The emissions stuff seems to depend on the gross vehicle weight and whether or not it was a California vehicle. (Oops, sorry. I missed the first part of your reply. There is only the one in the crossover pipe. Nothing after the converter.)

Please let me know how things go.

Hi TJF2019,

As for the o2 sensor, you most likely only have one. I found a diagram for the F-series which is the same as your except a van body rather than a truck (at least for this purpose they are the same) and it shows one location past the y pipe prior to the converter. The other is for super duty and others so if you only see one on your exhaust, I would not see any reason this is not correct. Also, the main reason is, this vehicle ran fine before with the way it is, so I wouldn't think it is an issue.

As for your issue of not being able to communicate with the PCM this is most likely a wiring issue especially if this happened a while ago and your vehicle still ran find. It could be an issue with the PCM and the data link but I wouldn't think the running rough and not being able to communicate is directly connected. However, if the tech traced the wires, I would assume they are ok but without more detail about what he actually did, we cannot rule it out.

As for your rough running condition. Pulling codes would really cut this down but here is what it sounds like to me. The fact that it runs ok after you disconnect the battery then starts running poorly actually points away from a module. The vehicle runs in what is called open loop when it starts. This means the PCM only looks at a couple sensors to determine air/fuel mixture. Usually this is just the engine and ambient/intake temp sensor and maybe MAP and baro. All the rest, such as o2 sensor are being ignored and it is running off of pre-programmed parameters.

Once it warms up based on engine coolant temp sensor it starts looking at the o2 sensor and seeing how it is doing in managing air/fuel ratio and starts adjusting accordingly.

Barring injectors just hanging open which is unlikely because this wouldn't be intermittent, I think you have an issue with MAF or possibly MAP. A scan tool hooked up can tell us this but without that option, we may need to test it off the vehicle, here is a procedure to clean it (link attached). Then a video on how to test it.

If you get those readings and let me know what you have we can go from there. Just make sure you monitor the voltage and see it nice and steady as you increase RPM and decrease RPM. Note your starting point at idle and then you max point and RPM if you can and if it the voltage jumped at all or reversed direction.

Just to explain the MAF, it tells the PCM how much air is coming in so that it can control the fuel to try and achieve 14.7:1 air/fuel ratio. There is a document attached that will basically say the same thing. However, if this is reading incorrectly, or telling the PCM that there is more air coming in then actually is, then it will load up with fuel to match that amount of air in order to achieve 14.7:1 air/fuel.

https://www.2carpros.com/articles/mass-air-flow-service

https://youtu.be/a6eaOd3ihiE

That's good to know where the O2 sensor fits into the ECM calculations. Also thanks for the info on the O2 sensor. These sensors are not small things and it was driving me a little nuts thinking I might have missed two of them.

I did start to think the MAF could be the problem as well. I'll check out the links to test it.

Hopefully the new ECM will fix the ODBCII problem so I can get codes. Thanks

Running rich problem solved!

It turns out this model doesn't have a MAF sensor. Instead it has a MAP (manifold absolute pressure) sensor. This sensor is on top of the A/C evaporator. It has an electrical connection and a vacuum line that runs to the back of the intake plenum. That vacuum line is PVC and had become brittle. It broke. I replaced the line and it solved the running rich.

Even though it runs good the "check engine" light is still on. I ordered a new ECM that will arrive early next week. I'll replace it to see if it fixes by ODBII port problem and give an update.

Nice work! let us know how it does with the new ECM.

Replaced the ECM and it made no difference. Engine light still on, ODBII doesn't work.

So I know this will be a "duh" moment for most of you but I'm going with the idea that my 1996 E350, at 9400lb GVW, is not an ODBII vehicle. I knew that going in but I swear I've seen a couple mechanics hook up to the ODBII port and read codes. I also thought that California vehicles did not get the weight exemption so I figured that's why mine seemed to work. I guess I was imagining things or just generally confused. It happens.

With this realization I tracked down the EEC port under the hood, put it into test mode, and had my digital volt meter flash coded numbers. I couldn't make out the specific trouble codes so I just ordered an ODB1 scanner tool and will figure out the remaining problems once it arrives.

In any case, it's running good now (in spite of the Check Engine light). Thanks for all the help!

Glad to hear it’s running well. If you get the other codes from OBD1 feel free to let’s us know what they are and we will help if needed.