EFI Gurus, I need your help! EFI Trouble Diagnosis

[luderchris]

Haven't run codes yet since I switched the hoses around, but it runs the same. I'll check to see if the 41/91 o2 codes are gone. The new BP sensor did get rid of the 22 code though.

 

[ransil]

where does the hose on the throttle body 90 degree fitting go to?? I think its picture2

 

[Sporto]

where does the hose on the throttle body 90 degree fitting go to?? I think its picture2

Randy,

He moved it. It was connected to PCV valve on driver's side valve cover. Now it goes to oil filler neck port.

Rich

 

[ransil]

Randy,

He moved it. It was connected to PCV valve on driver's side valve cover. Now it goes to oil filler neck port.

Rich

OK got lost in there..

 

[luderchris]

From my research, I don't believe my set up combo, including the 65 mm throttle body, should be a problem. Is that the consensus?

 

[chuzie]

Your EEC has already told you what the issue is. You have a fuel scheduling issue. It is either the aftermarket maf or the O2 sensors

 

[ransil]

From my research, I don't believe my set up combo, including the 65 mm throttle body, should be a problem. Is that the consensus?

If its not stock it could be a problem.

A dyno tune can take care of it.

I like to start with a stock setup , debug it then add the fancy shit, that way you know its right and where the problem is.

 

[Viperwolf1]

Have you checked to see if the O2 connectors are going to the correct O2 sensors? You might have them swapped.

 

[luderchris]

Your EEC has already told you what the issue is. You have a fuel scheduling issue. It is either the aftermarket maf or the O2 sensors

Ok. I will try another MAF. If that doesn't do the trick, I will try to swap O2 sensors left to right, then replace them if necessary.

I'm just concerned that it could be an injector, vacuum, spark plug/plug wire or fuel pressure regulator issue.

 

[luderchris]

If its not stock it could be a problem.



A dyno tune can take care of it.



I like to start with a stock setup , debug it then add the fancy shit, that way you know its right and where the problem is.

Wishing right now I had done just that, but with the 5.8L that was a little tougher than with a 5.0L. I know what you are saying though.

 

[luderchris]

Have you checked to see if the O2 connectors are going to the correct O2 sensors? You might have them swapped.

No. That is my next step after borrowing a different MAF to try.

Just for my own knowledge, why does left/right O2 sensors matter to the computer? Does it correspond to the side of the engine it is monitoring?

 

[Viperwolf1]

No. That is my next step after borrowing a different MAF to try.

Just for my own knowledge, why does left/right O2 sensors matter to the computer? Does it correspond to the side of the engine it is monitoring?

Because the computer is looking at O2 sensors and making fuel trim adjustments. If it sees a lean condition on one side and tries to richen up the other side because the harness connectors are swapped you still have problems and the computer won't know it. You don't have to swap the sensors to test it, just the connectors.

 

[luderchris]

Because the computer is looking at O2 sensors and making fuel trim adjustments. If it sees a lean condition on one side and tries to richen up the other side because the harness connectors are swapped you still have problems and the computer won't know it. You don't have to swap the sensors to test it, just the connectors.

Gotcha. Thanks Viper.

 

[luderchris]

My maf sensor and housing have no part numbers on them. To take a measurement of the housing, do I measure the diameter of the air inlet or air outlet side???

 

[chuzie]

MAF housing is measured at greatest restriction whether it be inlet, outlet, or somewhere in between.

I suggest you tend to the O2 sensors first, then the MAF.

 

[luderchris]

I suggest you tend to the O2 sensors first, then the MAF.

I'm going to swap the O2 sensor connectors to see if that changes anything, but I am also trying to figure out what MAF I have. Sensor has no part #, but I figured I can at least measure the housing.

Looks to me that the narrowest diameter is in the center and is about 55mm.

 

[chuzie]

Good eye. Looks like a 55mm MAF housing. There is no easy way to determine if that MAF sensor is matched to that housing so your best bet will be to bite the bullet and replace it. If it is not a player, you potentially have a spare sensor which is always nice to have.

FWIW- I think that may possibly be a Cardone reman MAF sensor p/n 74-9502 which is a match for the 91 Mustang 5.0. That being said, it is too much a risk, especially when troubleshooting a problem like this, to make such an assumption.

 

[luderchris]

FWIW- I think that may possibly be a Cardone reman MAF sensor p/n 74-9502 which is a match for the 91 Mustang 5.0. That being said, it is too much a risk, especially when troubleshooting a problem like this, to make such an assumption.

How did you come to this conclusion? The # on the sticker on the sensor?

 

[chuzie]

Yes. Pure speculation though.

 

[luderchris]

Yes. Pure speculation though.

Ok. Gotcha.