Wont run smooth when hot, 2.1 digifant

[Kuchster]

The last few days have been getting worse, there is a flat spot on take off when cold, but i would expect this from a cold engine. Now when the engine is hot, with a high ambient temp makes it worse, you step on the accelerator and it spits and pops and doesnt go, no power. I have checked the temp 2 sensor and replaced it, which both have good readings at different temps (as per bentley), afm is brand new a few months back, replaced the o2 sensor with brand new.

I have disconnected the temp 2 sensor and hooked up a decade wheel or variable resistor. The engine runs great with good power when i feed 1K into the temp sensor wire. The temp 2 sensor reads out at 280ohm. With the value higher at high temp, this makes the engine run more rich, so there must be some sort of fuel problem?
Fuel pressure is great, compression is 135 all around. Any suggestions on this one?

Thanks Kuch

[Wildthings]

Check to see if the wire to the O2 sensor is grounded out or not.

[morymob]

Your resister/higher rest is switching ecu to cold mode probably and at this point oxy sensor not used.agree, above with post,meter oxy wire for short of center to ground or to shield also in a ground.

[crazyvwvanman]

To expand on what others have said, the O2 sensor reading is ignored until the ECU sees a warmed up engine. Your added resister is simply telling the ECU to ignore the O2 because the engine isn't warmed up enough yet.

The green cable that the O2 wire plugs into is a COAX wire, with a center signal wire insulated from wire mesh outer wire that is grounded. If the cable gets damaged the center wire can touch the grounded outer shield wires and then the ECU gets a bad reading from the O2 circuit. Sometimes someone thinks to repair a bad end on the green cable and crimps a new end on it that joins the inner and outer wires without them realizing it.

Lastly, there is a special ground wire that the ECU used for the O2 circuit. It is a brown wire in the small wire bundle that goes to the distributor. The brown splits off from the rest and the brown is supposed to be screwed down against bare metal of the engine. If this wire is not well earthed to the engine the O2 reading will be messed up at the ECU.

Mark

[Kuchster]

The o2 sensor is brand new, so i wouldnt think it has much of a problem, the o2 wire is not grounded. I however noticed a split in the coax where the outer shield is cut off about 10mm from the inside cable, so i have cut this back and crimped a new spade connector to this. I have again checked the timing at high rpm per 10c method. I have removed the resistor and hooked the temp sensor back as original. When i rev the engine on idle without load, it has a flat spot, if i rev quick i can hear the afm flap hitting closed (backfiring through intake?) I have not driven it yet. Today while i had the resistors and it was running rich from take off, it revved, then slowed, then revved, while my foot was constant on the accelerator, though im guessing because it was just running too rich.

I have not yet checked the brown earth wire.

Thanks

[morymob]

Hope u didn't crimp new connector to the shield AND the center wire, NOT to be ANY connection between shield and center wire. Shield is grounded at ecu end ONLY.

[tkdkrav]

I would check timing too. Sounds like it's not advancing properly.

[tkdkrav]

Sorry - I missed the post where you said you checked you timing. Womp womp

[camerahunter]

It sounds to me like the AFM is not plugged in.
Maybe it is but this is exactly what happens when it's unplugged.

Cheers,

David
_________________
1984 - Daily driver

[Kuchster]

https://www.youtube.com/watch?v=gCtRpZGRU0E&feature=youtube_gdata_player

[Kuchster]

https://www.youtube.com/watch?v=gCtRpZGRU0E&feature=youtube_gdata_player

[Wildthings]

Popping can be caused by a lean condition or an intake valve that isn't closing.

[camerahunter]

So, I'm 0 for 1.
I am not familiar with 10c method of timing.
Did you do it with the idle stabilizer unplugged?
Have you set the idle with the stabilizer unplugged?

Cheers,

David
_________________
1984 - Daily driver

[Kuchster]

The crimped connector on the green o2 wire has only been crimped on the inner wire, not the outer shielded wire, this is cut about 15mm less than the inner wire.

Today it became even worse, when the engine was cold on take off, with acceleration constant, the engine went, vroom, dropped, vroom, dropped, so on, as if i was pressing the accelerator and letting go again.

When it was hot, i got on the freeway, you could hear the engine backfiring and couldnt get higher speed then 80km/h.

Got off the freeway, it sounded like 2 cylinders were not firing, pulled into the nearest side street, couldnt get to 40km/hr. Came to a stop at the roundabout and car started to spit and stalled, with about 20 cars behind me it would no longer start, i kept cranking, moved about a metre then had to throw it in neutral and try to start it again, at this point when it started it would no longer rev. I made a call, started the car and drove off again, it seemed to be fine until i got home, well not exactly running perfect, but it ran ok.

Got home and started to check it all out, starting the engine after each fix:
Fuel pressure was my first check, all ok, around 30psi
removed all engine grounds, sanded them and put them back on
had to cut my built in cupboards to remove the ecu, replaced it with known working one.
replaced coil
checked all pins on ecu cable as per bentley, checks out fine
changed the idle stabiliser relay behind the air intake pipe
checked for air leaks
replaced temp2 sensor
oxygen sensor brand new, no grounded wires
afm brand new about 2 months old
brand new leads not long ago
replaced coil and cap and rotor with known working one
timing checked and is spot on


What else could it possibly be? Injectors blocked? i have put in a new fuel filter a few months ago so im not sure that this could be possible. I run 98 octane fuel.

I have attached a video of it running in a post up above, not at its worst, you will see when i rev it that there is a lot of delay, and you will see the backfiring up the air intake.
Hopefully this might point me in the right direction

Thanks for the help so far

[Kuchster]

the 10c method of timing that i used was by punching another groove in the crank pulley, and timing at above 3000rpm. i have not set idle, i dont think there is a need, i did tune up the throttle switch last time, which is working correctly. Idle stabiliser is buzzing as it should.

[Kuchster]

And just before anyone mentions it, the cat is empty, as in, non existant, there is no blockage there.

[camerahunter]

With the idle stabilizer unplugged and the air adjusted at the base of the throttle body it will make a difference.
Warm it up before you start and then turn it off. Unplug it before you restart it, set the idle, turn it off and then plug it back in and restart. It might work. I don't know for sure but that is the correct way to set it and then the mixture is taken over by the ECU at operating temp.

I'm guessing again...

Cheers,

David
_________________
1984 - Daily driver

[camerahunter]

It's hard to tell much from the video. One thing I may have noticed is the AFM boot really looking like it might not be attached to the throttle body? It looked like the AFM rose higher then the engine during one of the hiccups. Hard to say for sure though because the camera is also moving and I can't see very fast.

Cheers,

David
_________________
1984 - Daily driver

[Kuchster]

The afm boot is very tight and leak free.

Though, i think i have found the problem..

They are in the ultrasonic now for a while longer, but looks like i'll be flushing the fuel tank and adding a few more filters.

Kuch

[camerahunter]

YIKES!
That's probably it.

Cheers,

David
_________________
1984 - Daily driver