Hey all, here's my problem. The car is an 87 with a TPI 350. I've noticed a fair drop in fuel economy over the last several loads of fuel. Normally if I'm gentle with her, I can average 20mpg per tank. For the past half dozen tanks, again driving gently, I made a best of 16.3. Also, there's a strong fuel smell in my exhaust. It is particularly noticeable when idling at traffic lights and immediately after shutting down when I park. There are currently no codes and the CEL is not on. She doesn't miss, there's no noticeable smoke coming from the exhaust, there's no fluid cross contamination, and she isn't using any fluids. When I drive, there is no power loss, and I even gave her a good romp at WOT up to 100 mph last night. I know that's not what anyone would call driving gentle, but I wanted to make sure I wasn't losing power or missing anywhere throughout the RPM range. She pulls as hard and runs as strong as ever.

So my current plan is to replace the oxygen sensor. I'm doing that mostly because its cheap, easy to do, and as the third owner, I don't know when it was last changed. My suspicions actually lean towards one or multiple injectors that are stuck open, and I did have plans to put a new set in once spring rolls around.

So I wanted to throw this out there to check with the community and see if I missed anything. I know this is kind of long, but I feel that the more information I can provide, the better someone might be able to help me. I know the car isn't supposed to get great fuel mileage, but I'd like to be able to get it back to where it was. Any thoughts, suggestions or questions are appreciated and thank you in advance.

 

good plan start with the O2

 

Check the fuel pressure while running & make sure it holds psi when engine is off, You might have leaky injectors or a leaky fuel pressure regulator.

 

 

If injectors are leaking down you would most likely have a hard time starting a warm/hot engine and TPI is known for no start when hot and leaking injectors.

I would suggest the coolant temp sensor is the problem, if it's reading to cold vs. actual it will run rich just like your saying but shouldn't hurt performance and will have poor fuel economy. If it's sending a signal to the ECU weather accurate or not a code will not be thrown

 

Hey, thanks for the suggestions ex-x-fire and TransAM Joe. Unfortunately, I will be unable to work on the car until Saturday. I'll go ahead and test the fuel pressure while I'm swapping the o2 sensor.

The coolant temperature sensor does make sense. If the ECM is getting a bad signal and thinks it isn't warming up, I can see how it would run rich trying to get the engine hot.

However, I do have a couple of questions about the coolant sensor. Does my dash gauge read from the same sensor as the ECM? I'm asking this because the water gauge shows normal operating temperature once the car gets warm. The car has never gotten real hot, but the once it reaches temperature the needle will sit on or just a little under the line that is between the 100 and 220 lines. In the three years I've owned it that has always been the normal temperature the car runs at. So if the water temperature is read from only that sensor, and it was sending the incorrect signal, wouldn't that also cause my dash to read wrong too?

Thanks again for the help, all your input is appreciated.

 

Temp gauge signal comes from sensor in drivers side head, ecu coolant sensor is on intake

 

I see. That makes sense now. Its more complicated than I would design it, but I find that to be true about my truck and my friend's Dodge as well. Thanks for the clarification, I guess I'll be swapping the coolant sensor on Saturday as well.

 

All right, I got the o2 and coolant temperature sensors changed out. I went ahead and tested fuel pressure while I was at it too. It showed 47 psi at fast idle. It dropped to 42 after shutdown and stayed over 40 for more than 10 minutes. It does feel good to rule out the injectors and pressure regulator.

The car has almost a full tank of fuel in it now, so all that is left is to run it all out, fill it, and see what numbers I get.

I am wondering about something though. I had to remove an object that looks like a larger version of the coolant sensor from the intake manifold to make enough room to swing a wrench on the sensor I was putting in. Coolant came out of the port that it was in when I took it out. Could anyone tell me what that is because I find it odd that there would be two coolant temperature sensors right next to each other in nearly the same spot in the intake manifold.

Anyway, I'd like to thank everyone for their help again and we'll see in a few weeks if the fuel in my exhaust is gone and if my fuel economy comes up any.

 

I second that one, lower than normal o2 voltage would drive blm's way up and could possibly be the cause of reduced mileage.