2G 1999 Mitsubishi Spyder GS 2.4L SOHC Stalls After Warm Up, No Codes

[Ken2469]

Hey everyone out there,
I have acquired a 1999 Mitsubishi Spyder GS from a friend. When the car is started it will run fine with no problem stepping on the gas peddle. After the engine reaches normal operating temperature, the engine begins to surge and if you step on the gas peddle to fast it will backfire and stall out. If you steadily give it gas it will begin to gain rpm's until you let your foot off the gas peddle and the same process is repeated. I have changed out all of the wires, the plugs, coil pack, MAF, IAC, throttle positioning sensor, cam sensor, crankshaft sensor. The car is in time and I still have no codes to read. Is it possible that it could be a blocked fuel strainer. It just seams odd that it happens when it reaches normal operating temperaturer. I will try to take a pressure reading off of the fuel rail to see if there is a drop in pressure when the temperature is up. Any ideas? Thanks in advanced

 

[delta448]

It really sounds like an error in fuel delivery. You need to see what the front O2 sensor is telling the ECU and what the ECU is trying to do with fuel trims when it reaches closed loop temp.

 

[Ken2469]

It really sounds like an error in fuel delivery. You need to see what the front O2 sensor is telling the ECU and what the ECU is trying to do with fuel trims when it reaches closed loop temp.

Not to sound to stupid, how would I preform that test?

 

[Ken2469]

Not to sound to stupid, how would I preform that test?

 

[delta448]

A data logger, any OBD2 scan tool that shows live data, or you could even use a wideband.

 

[motomattx]

You could have a bad coolant temp sensor also.

 

[Ken2469]

You could have a bad coolant temp sensor also.

Thanks for the info, I have already changed that out from the person that owned the car before. He said he changed the fuel pressure regulator, but looking at it I don't think he did. After talking with delta448 I ran a live scan on the car. The short term fuel trim was at about 26.2 percent and the O2 sensors were at about 0.020 Volts. I am going to check the fuel pressure regulator to see if it holds pressure and to also run a pressure test on the fuel rail. Thanks again for the help.

 

[Ken2469]

A data logger, any OBD2 scan tool that shows live data, or you could even use a wideband.

Hey Delta448,
Thank You again for the info. I ran a live scan and both 02 banks are at 0.020 volts. Kind of low, but my short term is at 24.2%. The previous owner said that he changed out the fuel pressure regulator, but when looking at it, I don't think he did. I am going to run a pressure test on the fuel rail, and a vac test on the fuel pressure regulator to see what I get. If you have any other ideas they would be highly appreciated. Thanks Again.

 

[delta448]

Have you replaced the front oxygen sensor? I'd be very suspicious of it, or at least what it's telling the ECU. The wiring from it may be damaged.

That 0.02V signal is telling the ECU that it's really lean, and the roughly 25% more fuel being added says it's been reading that way for awhile. Normally you'd investigate the fuel system when lean, but in this case, I really think the engine is probably running closer to stoich in open loop than once the fuel trims start being taken into consideration by the ECU.

Do you have any exhaust leaks before the front O2? Checked voltage delivered to the sensor?

 

[motomattx]

Try unplugging the mass air sensor when its acting up and see if it comes around.

 

[Ken2469]

Try unplugging the mass air sensor when its acting up and see if it comes around.

I'll give it a try in the morning. I'll disconnect the front O2 to see what results it gives me, I think I will check the voltage first, but I didn't find any exhaust leaks. I find it odd that the bank 2 O2 sensor is giving me the same exact reading as the bank 1. I would go out tonight but it's 16 degrees and snow and ice. Thanks Again. I will let you know what results I come up with.

 

[delta448]

There's only 1 bank of cylinders in an inline engine. The O2 sensors are upstream and downstream, as in relation to before or after the catalytic converter.

Disconnecting the front/upstream O2 sensor is the same as having a dead one. The ECU sees low (or zero) voltage and adds fuel.

Disconnecting the MAS however, will cause the ECU to stay in open loop among other things. Don't expect to be able to drive it with the MAS unplugged.

 

[DogWhistle]

It really sounds like an error in fuel delivery. ...

The cause may be more mysterious and surprising than you thought. You checked and replaced the right things, but this model has a secondary fuel pump relay, located on the driver’s side of the console, under the plastic cover. Mitsu used the switching function of this relay to vary the speed of the fuel pump. We’ve never found a good explanation as to why they felt this model needed this second relay. This relay fails and reduces the fuel pressure once the car goes to closed loop. Here is the article which shows you how to bypass the second relay:

https://www.dsmtuners.com/threads/4...mp-relay-module-bypass.497574/#post-153547515

 

[Ken2469]

The cause may be more mysterious and surprising than you thought. You checked and replaced the right things, but this model has a secondary fuel pump relay, located on the driver’s side of the console, under the plastic cover. Mitsu used the switching function of this relay to vary the speed of the fuel pump. We’ve never found a good explanation as to why they felt this model needed this second relay. This relay fails and reduces the fuel pressure once the car goes to closed loop. Here is the article which shows you how to bypass the second relay:

https://www.dsmtuners.com/threads/4...mp-relay-module-bypass.497574/#post-153547515

Thanks for the input. I just removed mine, I am looking at the wiring diagram for the bypass but I am not the best at electrical. It is stated that if you make three connections you could bypass the module. I can't see where the third is. I might go and buy a used one to make sure that is the problem before cutting out the wiring. I wish they showed a part number in the thread, but mine is MR239764. Thank You again for all of your help.

 

[DogWhistle]

Rather than try to buy a replacement relay, why not eliminate the overly complicated portion of a system as critical as your fuel pump?

Perhaps I should have phrased the rewire as having 3 (soldered) extensions: 1) The black with red tracer to the fuel pump relay, 2) The black with blue tracer to the fuel pump, and 3) The black with white tracer from the fuel pump.

After removing the wires from the secondary fuel pump relay socket, you connect the wires 1) and 2) above. Wire 3) goes to ground. The fuel pump will now run when the key is turned to the “On” position.

Hopefully, this will solve your problem and get you on the road.

 

[Ken2469]

Rather than try to buy a replacement relay, why not eliminate the overly complicated portion of a system as critical as your fuel pump?

Perhaps I should have phrased the rewire as having 3 (soldered) extensions: 1) The black with red tracer to the fuel pump relay, 2) The black with blue tracer to the fuel pump, and 3) The black with white tracer from the fuel pump.

After removing the wires from the secondary fuel pump relay socket, you connect the wires 1) and 2) above. Wire 3) goes to ground. The fuel pump will now run when the key is turned to the “On” position.

Hopefully, this will solve your problem and get you on the road.

Thanks for all the help, that was the problem. All wired up and running like a champ!!!!! Thank you for all your help again!!!!!