Okay so I need help in figuring out why I am getting only about 10-15 mpg on my 92 d16 motor!!!! I've done a couple things to it maintenance wise because it wouldn't start kinda still doesn't unless I throttle it. But anywho I changed the distributor cap and rotor , spark plugs and wires ,map and tps sensor, fuel filter and fuel pump. The only performance part was the fuel pump its a kemso 340lph. But could that really be it? What do you guys think?

 

There is absolutely NO reason for you to have a 340 lph fuel pump feeding an otherwise stock D16 engine. It isn't your only problem, but it darn sure isn't helping your fuel economy. Stop throwing parts at it and focus on monitoring the short term and long term fuel trims. Do you have any codes ??? Have you checked your mechanical timing (not distributor timing although that wouldn't hurt to check too) ???

 

What D16 motor and ECU?

 

Alright I will remove the pump when I get a chance. Yeah it's throwing an o2 sensor code but I changed it twice and its still telling me the sensor is bad. No I haven't checked my timing kinda don't really know how to do that. And its a d16z6 motor not sure on the ecu I'm guessing it's a stock one. Thanks guys

 

Post the actual CEL code.

Codes don't tell you parts to replace. They tell you what circuit to troubleshoot the problem.

 

I think the code was 41(heated oxygen sensor heater)

 

How do the plugs look? Sounds like a map sensor could be telling the car car to dump to much fuel. Bigger Fuel pump should not matter as long as the fuel pressure is set at 43, this is more computer or sensor related

 

The O2 sensor has 4 wires. Two wires are for the heater element and the remaining two wires are for O2 sensing. Test the two heater wires for power and ground using a multimeter.

 

I will take a look at the plugs and the o2 wires when I get a chance I'll be working the next couple days. How can I tell what pressure my fuel is at?

 

 

Yeah I would say it's running pretty good the only thing thats is in the mornings I when I turn my car on I have to throttle the gas to start it and when i run at low rpms and hold it at like 1-1.5k rpms in 1st and 2nd gear it starts to want to jerk

 

 

Unplugged the ect and the car wouldnt stay running unless I throttled the pedal

 

 

Well my car would eventually start and stay running with out the pedal throttling with the ect plugged in. Are you saying the car should stay running even with the ect unplugged? And I will be removing the pump when I get a chance and putting a stock one in

 

 

Good theory but you forgot the "fluid dynamics" portion of the calculations. When you increase the volume of liquid pumped through the same size hose, the pressure increases as well. The stock fuel pump creates fuel pressures around 34psi at idle under vacuum, whereas a Walbro 255 pump creates 46psi under the same conditions. The 340 will be even higher... essentially over powering the stock fuel pressure regulator.

The O2 heater circuit not working is a problem... the O2 sensor cannot function properly if it not warmed to at least 600' F. An exhaust leak can give false readings to the ECU and increase the fuel delivery to the engine which adversely affects the fuel economy. Low ECT readings would make the ECU think that the car is essentially operating like at cold start... also creating poor fuel economy. Odd IAT readings can create the same issues. You need the ability to monitor real time data while the engine is running to effectively diagnose these possibilities.

 

I think I'm going to just remove the pump just to take that out of the equation. Is there a way to monitor all that on a 92? Or would I have to take it to a shop?

 

 

 

 

You would need to measure the fuel pressure with a gauge. Too much fuel can cause one of the "O2 sensor" codes due to inability to reach fuel trim.

Assuming the car were completely stock (which it is not), the most common reason for low mpg is improper timing.

 

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