Low rpm hesitation and bucking

[slo]

This is on my 2.6 tn.. seeing as alot are fimilar with the magna efi i thought to try here

Ok so the problem is between 1400-2000 with about 20% throttle what happens is the motor hesitates, then bucks (cuts in and out completely) until it gets above 2000 where it smooths out. If i floor it from that range its fine, The motor runs completely fine other wise

I haven't driven the car in a year but last time it was driven it had this issue but only slightly, when cruising it would maybe once a month just buck once or twice when driving, but now the problems worse as it does it all the time.

So far ive replaced Coil, Igniter, Cap, Rotor, Leads, Plugs, Airflow sensor, ECU, Injectors, Fuel reg, TPS, idle motor/idle switch
Have checked-
Dissy signal, Coolant sensor (whether plugged in or not still problem), and Injector signal(oscilloscope from ecu),Pritty much all the wiring
Ive taken the fuel pump out and checked the sock on the end which was fine, have ran the pump with out the motor running and all seems to be sounding fine
Compression is good, no air leaks either
Checked all signals and are all within spec

The only thing ive noticed is that it doesnt do it with the air flow sensor unpluged, i would drive around with out it but it runs too rich without

So any ideas im at ends with it now!!

[LEE]

air flow sensor-try cleaning it with carb cleaner, then dry it with compressed air and see how it goes

[slo]

ive already replaced the air flow sensor, both are doing the exact same thing, ive tried cleaning one but yeh didnt do anything

[Superscan811]

Did you replace the TPS with a new one or a 2nd hand one?
The 20%-40% throttle is the most used area of the TPS to wear out.

With the ignition on but the engine stopped AND using an ANALOGUE multimeter,
measure the voltage coming out of the TPS. The needle on the multimeter should move smoothly with NO flickering.

Any flickering and the TPS isn't in good shape.

If it is the TPS, try filling the inside of it with WD40.

Cheers.

[sceneybr]

Had a similiar problem a while back i wouldnt be surprised if its the fuel pump and the bucking is it starving cause higher up it went fine for me but it ended up being the pump of and fuel filter a bit blocked check those for a cheap fix

[slo]

Did you replace the TPS with a new one or a 2nd hand one?
The 20%-40% throttle is the most used area of the TPS to wear out.

With the ignition on but the engine stopped AND using an ANALOGUE multimeter,
measure the voltage coming out of the TPS. The needle on the multimeter should move smoothly with NO flickering.

Any flickering and the TPS isn't in good shape.

If it is the TPS, try filling the inside of it with WD40.

Cheers.

That's a good point, it was replaced 2nd hand

ill be testing that out tomorrow with analogue multimeter for sure, but the only thing is with the tps unplugged it still does the exact thing but ill test it anyway

[slo]

Had a similiar problem a while back i wouldnt be surprised if its the fuel pump and the bucking is it starving cause higher up it went fine for me but it ended up being the pump of and fuel filter a bit blocked check those for a cheap fix

the filters about 5k old, ive got a spare but the problem is its exactly like clock work it seems to like too electrical to be that, that and unfortunately there about $50 a filter for these cars... its a joke
the pump crossed my mind but got a adjustable fuel reg with a gauge (been replaced with another one) and at very very rare occasion it happens while im under bonnet it seems to keep steady pressure... but still replacing the pump has crossed my mind just so i can tick that off the list too

oh thats the other thing, when its cold just after i start it if i rev it a little the revs fluctuate up and down from 1300ish to 1800ish even tho my foot is steady then all of a sudden something happens then it stops and settles where it should be normaly around 2200ish. i can also get it to do this when i go to take off just when it starts bucking i clutch it, it fluctuates a but then i can take off smooth till i change gear then its back but i cant always do this

whats seems to be happening is the injectors are shutting off its reminds me of when i come around a corner on low fuel, misses a little then cuts in out a bit then once ive straightened up it picks the fuel up and all good cept its doing this even on a full tank

[LEE]

yep try TPS , tried to drive mine with tps disconnected and it didnt like it at all , dont forget to reset the ecu , then set idle speed and tps

[slo]

how did yours react with out the tps pluged in??