88 Pathfinder, No Idle

[BattleAxe]

Well, I can usually figure these things out my self, or with a little research, but right now Im stuck, so I joined this forum. Ive spent some time here before just looking at cool things to do to my pathy, I really do want to fix it up a bit some day. Huge nissan fan, more for the cars though than 4X4, but Id love to get into it.

 

Anyway, 88 Path, 3.0, 4X4. Died on me a few days ago while downshifting, then wouldnt start. After sitting a while/me tearing the air cleaner apart and putting it back together, it started up and drove fine for a while, then died while downshifting again. Kept doing this, "fixing itself" after Id messed with the air cleaner, but getting much worse until not starting at all.

So I replaced the carb, and it started to start again, but no idle. Replaced the fuel filter, O2 sensor next, same problem.

 

Heres exactly what its doing now: Starts, but only if pressing the throttle, otherwise it just sputters. Once it does start, it will not stay running unless pushing the throttle 1/4-1/2 way, otherwise it just dies immediately. If I push the throttle to keep it running, it revs way up, but then bogs down and tries to die even though I have not let off the throttle. It will only keep running if I push the pedal more and more. I have revved it up to 6k, but it will die unless I pump the throttle.

 

I have done my best, but am at a loss, and getting sick of working on this issue hours on end every day after work. Huge props and thanks to the guy who helps me out here. I hate being this angry with my BattleAxe

[Kingman]

MAF sensor or wiring probably, it's attached to the driver's side of the throttle body. Try unplugging it and see if it runs any better, be warned it will hit a 3K rev limit (limp mode). Also make sure the connections are squeaky clean.

 

Sorry to hear you wasted money on the O2 sensor, it will never make a TBI truck run bad enough to notice. They only operate above 2,800RPM and under certain parameters.

[Slartibartfast]

You say it got better when you messed with the cleaner... this makes me think, A, there's a crack between the air cleaner and the throttle body (I know there's a rubber pipe that can crack or lose a vac hose on the MPFI trucks, dunno about TBI though), or B, it's temperature-related... is it still getting worse each time you try starting it? Maybe check the coolant temp sensor?

[amo1dun]

 

 

Sorry to hear you wasted money on the O2 sensor, it will never make a TBI truck run bad enough to notice. They only operate above 2,800RPM and under certain parameters.

 

II disagree, I have an 89 tbi and when the o2 was shot and still plugged in it was by far the worst driving experience ever....it caused harsh shifting, choking, sputtering and just ran like complete doodoo!!

[BattleAxe]

Thanks guys. I figured when i swapped in another carb, I had a good pretty good chance of solving the issue because so many things are built in to it. It would make sense if the MAF wiring was bad though... Ill chack that out now. Its pretty consistent doing just what I said at the end of my first post. For a while there it wouldnt start at all though, until I replaced the carb... So it seems like I have something there. About the O2 sensor, that good to know. I work at the junkyard, so I promptly decided to try a used one for $1.99, rather than pay the parts stores $140.00.

I know a MAF will make Nissans run just about like this, I wasnt entirely sure that the TBI ran off of one though, I thought that was just TPS. About the air cleaner, That definitely had me fooled for a while, and I spent a lot of time on it, but I think it was all just coincidence. As far as coolant temp: would that really make it run this poorly?

[amo1dun]

Thanks guys. I figured when i swapped in another carb, I had a good pretty good chance of solving the issue because so many things are built in to it. It would make sense if the MAF wiring was bad though... Ill chack that out now. Its pretty consistent doing just what I said at the end of my first post. For a while there it wouldnt start at all though, until I replaced the carb... So it seems like I have something there. About the O2 sensor, that good to know. I work at the junkyard, so I promptly decided to try a used one for $1.99, rather than pay the parts stores $140.00.

I know a MAF will make Nissans run just about like this, I wasnt entirely sure that the TBI ran off of one though, I thought that was just TPS. About the air cleaner, That definitely had me fooled for a while, and I spent a lot of time on it, but I think it was all just coincidence. As far as coolant temp: would that really make it run this poorly?

 

A bad coolant temp sensor can cause ur rig to start intermittently or not at all...

 

Did you check this ecu for codes?

[Leo94]

Looks like OP made the same mistake when we got our trucks. What seems like a carby is really TBI (Throttle Body Intake) so it has one injector on the throttle body. I suggest going HERE to learn more about the TBI parts.

[krmiller07]

I would also check the fuel pump in the gas tank !

[BattleAxe]

Fuel pump is good. I checked for codes, got just the 10, 20, 3, 4, & 5 which look like nothing, but then I unplugged the coolant sensor behind the timing cover and the problem got just SLIGHTLY worse, but same characteristics.

[Kingman]

Those aren't codes. Red light is the first numeral and the green light is the second. Example 3 red blinks and 2 green blinks is code 32. Not code 3 and 2.

 

The CHTS being unplugged making it run worse is a good sign, means it's doing something. A cold engine without the CHTS is almost impossible to start and drive, been there done that. Unplugged and warm/hot it's usually fine. That sensor is the main source of info for the ECU to adjust the fuel mixture, without it at all (cold) or a poorly working one creates all kinds of hell. The changes in the cylinder head temperature are relayed to the ECU via resistance. Too much or little makes it think it's in the Antarctic so it floods the engine out. I went through a half a tank of gas in 14 miles due to mine going bad. Fouled the plugs and clogged the catalytic converter too. That also brings up another thing that should always be checked along with the CHTS and that's its sub harness. If that's corroded, cracked, frayed, anything the ECU won't get the right signal regardless of what the sensor is putting out. Sometimes that's the root problem and not the sensor it's self. It would all make good sense but not if it's related to your tinkering with the throttle body.

 

I think you've got a MAF issue or like was said above a leak in the throttle body somewhere. They don't run real well, if at all, without the air cleaner on.

Edited May 18, 2012 by Kingman

[BattleAxe]

Those aren't codes. Red light is the first numeral and the green light is the second. Example 3 red blinks and 2 green blinks is code 32. Not code 3 and 2.

 

The CHTS being unplugged making it run worse is a good sign, means it's doing something. A cold engine without the CHTS is almost impossible to start and drive, been there done that. Unplugged and warm/hot it's usually fine. That sensor is the main source of info for the ECU to adjust the fuel mixture, without it at all (cold) or a poorly working one creates all kinds of hell. The changes in the cylinder head temperature are relayed to the ECU via resistance. Too much or little makes it think it's in the Antarctic so it floods the engine out. I went through a half a tank of gas in 14 miles due to mine going bad. Fouled the plugs and clogged the catalytic converter too. That also brings up another thing that should always be checked along with the CHTS and that's its sub harness. If that's corroded, cracked, frayed, anything the ECU won't get the right signal regardless of what the sensor is putting out. Sometimes that's the root problem and not the sensor it's self. It would all make good sense but not if it's related to your tinkering with the throttle body.

 

I think you've got a MAF issue or like was said above a leak in the throttle body somewhere. They don't run real well, if at all, without the air cleaner on.

 

What is the significance of the different length of flashes then?

 

The coolant sensor harness looks good, but I have yet to replace the sensor itself. Repalcing the carb involved replacing the MAF as well so I do not believe that is my problem either. It ran just fine before without the air cleaner on, I was even able to make it up and down the street without it or most vacuums hooked up. I think my problem is a bit bigger.

 

I do appreciate the help, Im going to replace the coolant sensor tonight, looks like its gonna be a pain. Thanks again, Im still open to more suggestions until I get this figured out.

Edited May 18, 2012 by RedPath88
Fixed Quotes

[amo1dun]

Hey bud...read my thread in "THE GARAGE" "HOW TO" section....its called "Engine Coolant Temp Sensor", It explains how u can swap that temp sensor easily without taking off the tbelt cover.....also, to check ur ecu codes...turn ur key to " ON" and flip the toggle switch on ur ecu to "diagnostics" ...when the red light blinks 3 times flip the switch back to "OFF" ur ecu will blink ...count the red flashes followed by the green ..red equals 10s , green equals 1s.......example, 3red then 3 green is 33... ...55 is normal operation...tell us what u come up with....cheers

[RedPath88]

What is the significance of the different length of flashes then?

 

NPORA Forums > General Topics > The Garage > How To's > ECU Self Diagnostics for 87-95 Pathfinder

[BattleAxe]

Ran the codes again. First thing I saw as the Coolant temp sensor so I practically ran to Autozone to get one, replaced it, put everything I tore apart this week back together, and its doing the same exact thing. I closely inspected the wiring harness for the sensor itself, and it looks fine. I even cleaned it. Then I inspected the engine wiring harness all the way back to the ECU itself. No rubs or anything. Checked codes again: 13 and 11. 13 is the temp sensor and 11 is the CAS. It may have been there before, I dont remember if I waited to see all the codes after I saw the 13. Is that a normal code to be stored? I know my 240 had a couple that were always present but not a problem which is apparently normal. I guess whenever I can get a ride to the junkyard Ill be grabbing that small wiring harness and trying that... Because I do still have the code 13 as of now.

[Kingman]

Check the resistance of the two CHTS wires from the ECU pins to the plug on the sensor. That'll rule out the CHTS wiring entirely. You can also dunk the new sensor in hot water and watch the resistance change. I wouldn't put much faith in the Autozone sensor though. Kinda weird the CAS code came up, there may be a ground issue somewhere. Have you checked those real well? The CAS, MAF, and CHTS I believe are grounded on the same circuit and Nissans are pretty finicky with their grounds.

[BattleAxe]

I dont have an ohmeter to check current, so I cant get very far there. I swapped that small harness to the CHTS and it did nothing, then I swapped the ECU and it still acts the exact same way, though when I scan for codes it just reads 44 "ECCS Normal Operation". All grounds are good as far as I can tell. Just kind of an update, Im really getting nowhere with this, and Im almost considering just letting it sit and focusing on a different mode of transportation so I can just do my fuel injection swap. This motor is no good anyway, burns a quart of 15w-40 every few days, no compression/no power, and I have a 150k mile vg30e sitting in a friends shop that i probably could have had in by now if I hadnt been wasting my time with all this little stuff. This motor never gives up on me and has been very reliable depite its condition, but Im done with looking for this tiny little thing thats causing it two sit on the street for weeks.

 

Thank you guys for all of your help, and I will still try little things here and there probably, but Im kind of taking a break from spending all the time and money on it right now.

[Slartibartfast]

15W-40?

 

At this point, if you've got a new engine... might as well. You might even find the problem while you're pulling the old one!

[BattleAxe]

Haha yeah... like i said it burns oil like crazy, so I run diesel oil. Way thicker for better protection and it burns alot slower. Like I said, this motor has been super reliable until now, if I could get it going again I know it would get me until Im ready to do a swap, but so far Ive wasted almost two weeks on it where I feel I could have been getting alot more done. It only makes about 75hp, So Id really like to get that fuel injection running good because I know that engine has good compression.

[BuckRyp]

ok i see a lot or talk about ecu in here, what does it mean when both red and green lights blink at the same time?

[RedPath88]

ok i see a lot or talk about ecu in here, what does it mean when both red and green lights blink at the same time?

At the risk of this being at what point are you getting this and did you read through the ECU thread from the link above?

 

Here is that link again:

NPORA Forums > General Topics > The Garage > How To's > ECU Self Diagnostics for 87-95 Pathfinder

Both lights will flash together during the mode selection process (see link) and during mode 2 to signify that the air/fuel mixture is cycling properly (see link).

[BattleAxe]

Just a heads up for anyone looking at this thread with a similar problem:

My issue was the hose running down from the AB valve. I plugged it off and it fired right up. Reading through the descriptions I didn't think it would cause such a problem but it turns out it must have been letting a bunch of air in past the MAF, which then couldnt make a reading for it to compensate. My hose was cracked and disintegrated completely when I pulled it off, and since I couldnt find something to properly replace it I just plugged the thing off. It works but does increase the chance of backfiring.