87 TII S4 low rpm hesitation
 

So here it goes been trying to figure this out for a while now the car is all stock it turns on and idles perfect but when I'm driving it warm or cold I get a hesitation at low rpm if I give it too much gas it only sputters a few times then it runs fine once the rpms build up it doesn't do it in the higher rpms only in the lower so far I've....

Checked the timing
Checked the coolant temp sensor
Checked and adjusted the tps multiple times and even tried another one I had laying around
Tried another AFM I had and another boost sensor I had also another ecu and still no difference
Replaced plugs,fuel filter,plugs and wires, fuel pump strainer,and fuel injector orings
Tried running it straight downpipe to see if it made a difference no luck

Its left me scratching my head don't know what else it could be any help would be greatly appreciated

just cleaned all the grounds by sanding all conections made no difference any help anybody?

sanding all grounds only helps if they are dirty..
or helps you find that the bloke before you left off the little one on the nest or the braided line back to the firewall



but the main cause of the " bad ground " hesitation is a fail in a crimp join in the loom about a foot out from the ecu plug

here all the instrument earths, the ecu earth and the noise shielding all tie together and the issue is fixed properly when you resolder the brass join,, and add a strap from it to the ecu case ( and bolt it down )

then of course comes all the other common errors that cause a hesitation
such as a bad TPS ( dead spot in its wipe movement or badly calibrated )
dirty injectors
faulty trailing coil etc etc etc

Okay so I'll solder all the wires off the crimp back together adding an extra wire? Then bolt the other end of the extra wire to the ecu mounting bolt? I'll give it a try in the morning cross my fingers and hope it works as far as the tps goes no dead spots on my nice fluke meter the coils also checked out fine haven't had the injecrors cleaned but did replace all the seals and orings on them

You might have in the process of cleaning up the gunk at the fuel tank sent more dirt deposits into the fuel line and clogged the newer injectors. And make sure the boost sensor vacuum line has the restrictor pill in it. It is usually located very close to the sensor.

Restrictor pill is in place just added solder to crimp grounds and added the extra ground to the ecu mount re did the grounds to the battery as the ground to the strut tower had no bolt in it also cleaned the ground under the coil pack and the hesitation is still there I'm going to pull off the uim again and check the lines going to the fuel injectors also going to replace the intake gasket while I'm at it even though it looks fine at this point I'm thinking its strictly fuel related so I'll do a fuel pressure test and see what I find

Which ground under the coil pack did you clean?

its not for the engine i beleive its for the cluster and other stuff but its a conector with 5 pins that plugs right into the tabs mounted right under the trailing coil

Your focus might want to shift towards the primary injectors.

I figured that I'll take off the manifold and blow out the fuel lines going to the injectors also clean the fuel rails

And make sure the replacement boost sensor is the proper model #. You have an S4 turbo so an NA sensor would not work.

Its a n 318 boost sensor

Can you retest the voltage w/key to on at the Brown/Red wire but do so after you unplug the vacuum hose to the sensor and cap this hose. Also, make sure you have the vacuum hose connected to the correct vacuum source as specified in the vacuum diagram. You can't use just any vacuum source for this sensor.

its plugged into the correct spot according to the diagrams ive seen

here are the readings exactly the same on two different sensors i tried

brown/red stripe-1.46v

brown/white stripe-5.0v

black/white stripe- 9.9v

like i said two different sensors and i get the exact same reading

Rx7 turbo 2: http://youtu.be/k3YD5SSPL6g

Here's a video of it idling after warm and you can kind of hear the hesitation at the end of the video under load you really feel it though

Until you clean the injectors it's going to be rather hard figuring out your problem. Until that time comes there's a couple of things you could do. There's a 4 wire Green check connector plug near the lead coil. W/key to on what does the B/W wire read? It should read 12 volts but it's the same wire at the boost sensor so I wonder if the voltage reading is the same. Another thing would be you could bypass the fuel pump relay and resistor. It's under the AFM. Has a round plug w/6 wires. When unplugged jumper one of the Blue/Red wires to one of the Blue wires.

Jumpered the wires you said and the hesitation at low rpm was worse and it was like it was running way too rich smell of exhaust burnt my eyes

Oh well.

Lol oh well? I'll have to look at the primary injectors and clean them could the fd fuel pump be causing the hesitation

To clean the injectors you would have to have them serviced by a professional.


The FD pump should not be a problem unless it was getting insufficient voltage. Earlier you were asked to check the B/W wire at the check connector. How about it and check it while idling also. It's possible your voltage is too low to the pump but it's just a possibility right now.

when he jumped around the fuel pump double speed relay he proved that the pump is pumping plenty ( when at full current )

and that it is also idling on the low speed setting
( hence it got fummy when jumped )

it does however indicate his fuel reg isnt coping with the large pump at low demand when on the high speed setting from pump control relay / resister



i would think that maybe it is hinting that the fix is in an aftermarket reg

Checked the B/W wire and it was about the same as at the boost sensor 9.99v

Was this w/key to on and if not then what is it?

Both with key on

But what about w/the engine running? And the advice of Bumpstart should not be ignored.