Help - Engine dies when MAF connector is removed. (1 Viewer)

[chukstel]

Hello everyone in the house, I need help solving my high fuel consumption issue on my LC 2000 year v8 4.7l 2uzfe with 177,000 plus.

Scan the car with gs500 scan tool with no check engine light and no codes.go through the live date with following : SHRTFT1-3.7, LONGFT1-19.0, SHRTFT2-4.7, LONGFT-17.6

After watching some YouTube video that says it is related to vacuum leaks, I checked all through the hoses with no leaks then I have to rethigten all bolts on the intake manifolds, clean the Injectors and spark plugs.

When I restart the car and check live data, the shrtft1-1, longft1-8, shrtft2-0.8, longft2-6. When I unplug the MAF connector the car will die down and when I restart the engine running the live data longft1 & longft2 went up.
Questions-- is the engine suppose to die when the MAF connector is unplug,
I also tried using the Techstream, it scan the engine when engine is off but cannot connect when engine is running, what can be the problem.
The Gs500 scantool scans the engine running and gives me live data. I cannot attach the video saying does not allow the extension don't know what it means.

Thirdly, can anyone tell me how the hose connection to the fuel pressure regulator works? Does it suck in air or push air to the fuel pressure regulator? If I remove the hose from the fuel pressure regulator it does not make any difference on the engine either increase or decrease the engine speed. (hose circleon picture)

I am doing all this as I don't have enough money to just throw in parts.

FYI- all spark plugs and coils are brand new replaced when it was given misfire on some cylinders and all stops with no codes. Injectors all serviced too.

I will appreciate all suggestions thanks in advance and please sorry for the long writings.

 

[chukstel]

Update on things done so far
Engine still dies when I unplug the MAF Connector.
When I raised the engine RPM 2300 the Longft1 and longft2 goes low to 1.6 and 0.8 with both shortft1 & 2 fluctuating between 0.8 and 0.
TPS % is 16.1 (before raising RPM tps% is 12.9) and when engine is off tps% is 14 don't know if this is the correct position.

I have checked around with no vacuum leaks around the tops and hoses.

Can anyone direct me as to what next to check please. I cannot drive far distance because of the fuel consumption. Reason I am working on this car.

 

[87warrior]

Engine still dies when I unplug the MAF Connector.

This is normal behavior, at least in my experience. However, mine will start with the MAF unplugged.

TPS % is 16.1 (before raising RPM tps% is 12.9) and when engine is off tps% is 14 don't know if this is the correct position.

I have never seen my TPS drop below 14%.

Can anyone direct me as to what next to check please. I cannot drive far distance because of the fuel consumption. Reason I am working on this car.

What does the fuel pressure look like?
What volume of air does your MAF indicate when it is running rich?

Tagging @jerryb since he had a lot of good insight of the 100's fuel system when I was diagnosing a stalling issue.

 

[jerryb]

I don't really know a whole lot about the throttle set up on the early ones.

I would compare my MAF readings with what are normal ones found online.
SOme cars will start or run with a MAF unplugged. depends on the car.

the vac line to the fuel pressure regulator pulls up the spring/diaphragm to let most of the fuel return to the tank at idle. Without the signal line the ECU may or may not be tempted to pull fuel.

There are good you tube vids on return type pressure regulators.
I'd check fuel pressure, look for fuel rail leaks, injector problems. Although you said injectors serviced
I'm leery about anyone else touching injectors and fuel rails. It's easy to make mistakes.
Then of course, bad MAF, bad o2 sensors.

I'd probably go buy a new MAF. If it drives normal and just has an idle problem then I think someone who's all up to speed on the apps and tapps or whatever it's called would be better able to help you.

check for vacuum on all the ports on your airbox.
maybe swap in a new o2 sensor.

 

[jerryb]

I forgot, I'd for sure check that MAF is reading ambient temp, intake temp, and coolant temp correctly.

 

[chukstel]

This is normal behavior, at least in my experience. However, mine will start with the MAF unplugged.


I have never seen my TPS drop below 14%.


What does the fuel pressure look like?
What volume of air does your MAF indicate when it is running rich?

Tagging @jerryb since he had a lot of good insight of the 100's fuel system when I was diagnosing a stalling issue.

Thanks for the reply. For the fuel pressure I don't have the pressure meter to do the reading. My mechanic recently changed the fuel pump as its slow to pick up when you step on the throttle.

The MAF reading is 5.46gm/s

 

[chukstel]

OK. I will plug in the scan reader tomorrow and check for those readings. Any idea what the correct reading should be?

Thanks

I forgot, I'd for sure check that MAF is reading ambient temp, intake temp, and coolant temp correctly.

 

[chukstel]

I don't really know a whole lot about the throttle set up on the early ones.

I would compare my MAF readings with what are normal ones found online.
SOme cars will start or run with a MAF unplugged. depends on the car.

the vac line to the fuel pressure regulator pulls up the spring/diaphragm to let most of the fuel return to the tank at idle. Without the signal line the ECU may or may not be tempted to pull fuel.

There are good you tube vids on return type pressure regulators.
I'd check fuel pressure, look for fuel rail leaks, injector problems. Although you said injectors serviced
I'm leery about anyone else touching injectors and fuel rails. It's easy to make mistakes.
Then of course, bad MAF, bad o2 sensors.

I'd probably go buy a new MAF. If it drives normal and just has an idle problem then I think someone who's all up to speed on the apps and tapps or whatever it's called would be better able to help you.

check for vacuum on all the ports on your airbox.
maybe swap in a new o2 sensor.

Thanks. Regards the fuel pump and Injectors are done by the dealership here, I call them my mechanic.

They are just asking I throw in a lot of parts into it, os sensors, MAF, fule pressure regulator all at once.

Initially they told me it's the ECM that is faulty and needed to be replaced, I told them I would not pay for the ECM if it did not solve the problem and they renege on it before asking me to change all those parts at once.

For the vac input to the fuel pressure regulator, there is no air suction in or out from the box, don't know if that is the normal way.

 

[87warrior]

The MAF reading is 5.46gm/s

That is a normal reading for MAF at idle. I expected (or was hoping) your reading to be much higher with the rich fuel mixture you are experiencing.

For the vac input to the fuel pressure regulator, there is no air suction in or out from the box, don't know if that is the normal way.

I noticed no difference in fuel pressure (or fuel economy) with a 350k mile fuel pressure regulator vs a new OEM. There was also no difference with the vacuum line connected or disconnected.

When you hook up the OBD reader, check to see if the o2 sensors are quick to respond. Slow o2 sensors are often bad sensors. Also watch the MAF response rate and watch for any inconsistent spikes in the results.