savanna.seven

iTrader: (5)

So once again, im plagued with stuttering throughout the rpms. At any load. 90% of the time as soon as the secondaries kick on it runs fine.

Stock S4 TII
Rebuilt Motor.
7ish thousand miles.


NOW BEFORE YOU SAY CLEAN YOU INJECTORS.
HAve been cleaned and flowtested TWICE. Didnt fix it last time but for some reason just swapping them with spares then back again made the issue go away.

Im really stumped on this one.
It gets bad to the point it cannot accelerate. Has no power whatsoever. Stutters extremely bad. Earlier i just gradually lost speed and the more i presed the gas the more the car slowed. Rpms would NOT go up. Just gradually fall. Till i clutched in and it stalled.


So far.
New Plugs and Wires
Swapped TPS 3 times, All were within spec.
Swapped MAF
New Fuel Filter and Fuel Pump Sock
New Manifold Gaskets
Compression Tested 100PSI on all Faces


Possible bad ground? even though its grounded properly?
Ive been driving for 7000miles prior and now this issue shows up?

j-roberts22

iTrader: (5)

More often then not it's a bad ground check the ground that runs to the tranny bell housing and the one that is connected to the top mount bracket bolt both very important one is the Ecu ground and will cause hesitation all day
-justin

j-roberts22

iTrader: (5)

Make sure all ur grounding points a clean use a wire brush also the terminals
-Justin

savanna.seven

iTrader: (5)

Ive cleaned the ecu ground and put a new bolt and wire for the one on the shock tower. The ground for the bellhousing is also new. Is it possible for the ecu ground to become loose? Afyer rdbuilding the motor and swapping evrrything in i torqued everything down to spec and recently cut open and redid the engine harness not too long agao.

What would happrn if i unbolted the ecu ground amd ran the car with no ground. How bad would it act.

satch

iTrader: (1)

The ground for the ECU is located on top of the manifold. The ECU does not ground to the body of the car. It might be fastened to it but it doesn't receive the necessary ground that way. And you might want to make sure the primary injector plugs are properly secured to the injectors themselves. If they are then pins 3E and 3C would have battery voltage w/key to on but engine off. And you might also want to measure the voltage on these two pins while the car is idling and operating at different rpm's under 3800.

boosted414

iTrader: (30)

The ECU is actually grounded to the top of the rotor housing :>

savanna.seven

iTrader: (5)

Yea i was saying i cleaned tje ground on the shock tower AND the ecu ground on the rotor housing. Clips are good and the injectors are good. Im curious if i were to unground the ecu on a perfectcrunning fc would it not run at all or run like **** due to the failsafe readings for each sensor

satch

iTrader: (1)

Just because the injectors and their clips are good does not mean the ECU is sending the proper signal to the injector which would explain why you might want to check the voltage value w.the engine running.

savanna.seven

iTrader: (5)

ok i see. what would cause it to not send the right signal? or is that a 100% bad ecu

rx-7 obsessed

if you can get your hands on a node light kit you could plug it into the injector connetor and turn the car over and see if the light blinks if it does this indicates spak u can also do it if you have a lab scope ( oscilloscope) to see the pulse sent
to the injector or swap out the computer with a know good one, i had a car that did this all the time untill the motor would go into boost then would run fine i tried a simple test by unplugging the map sensor on the pass shock tower im not recommending this by any means just something i have seen , i found the cause later of a broken wire from that sensor to the computer , if you dont have access to any of my previous ideas you can try this but dont leave it that way or drive the car
for any period of time.

savanna.seven

iTrader: (5)

Ok so i just got done with the car for tonight.
I cut the ecu ground wiring and heatshrink/crimped a new terminal. Re tapped the threads for that bolt hole on the housing and wirewheeled the top of it. Ran new 10g wire from the bellhousing to firewall. Checked and double checked all vac lines. Put back together Nd started it. Idled at 800 smooth and intermittently would break up and die. Or i could hold the throttle lightly and keep it alive.

I shut it down looked it over again. It ran better than lasttime which was good. But still stuttering when blipping the trottle to rev it. Now i unhooked my fcd and nothing chNged. Then i unhooked it completley and plug the sensor bCk in without the fcd and the maf made a wierd noise like a harely motorcycle and stopped. The car rN noticably better. Ive narrowed my issue or rather symptom down to now it trys stalling out or stuttering if i press the trottle to wot. Instead of rpms rising, ypu can go loght throttle and raise the rpms then go wot and you can hear the maf sucking abnormally loider and the rpms just hit a wall and drop

boosted414

iTrader: (30)

swap the afm out with a known good one and see if that corrects the issue

savanna.seven

iTrader: (5)

I had already tried. Thats the wierd thing.

boosted414

iTrader: (30)

ok so if you go WOT it sputters out? Are you sure its WOT and not when it hits boost? I had a similar issue. I know we have beaten the grounding issue for the ECU to death BUT hear me out.. run a 8-10ga wire from the battery negative to the block. Sounds crazy but I had this issue a long time ago and it turned out the block to chassis ground had some resistance in it.

savanna.seven

iTrader: (5)

I almost did that lastnight.
Well I think i may have it narrowed down now.
When the issue first happened and i got stranded my fried brought his spare TPS and we swapped it. Didnt change anything so we left the car at that that night.

well i ended up probing the TPS and his reading had a dead spot after 1.8ohms.
I pulled his off and probed it for the hell of it and with the plunger full out it read like 300ohms...wtf. I probed mine and it read a nice 5.5. So i put mine back on now with all the4 new grounds and such and it ran WAY better. Not 100% but i can drive it again.

NOW HERES THE FUNNY THING. I probed the TPS from the Sensor side and it read fine. 1.0 closed and 5.5 WOT or fully extended. now probing from the ECU side it read fine..but every other sweep the readings would be inconsistant so im thinking either wiring to the TPS or the ECU now.

boosted414

iTrader: (30)

So sensor side (at the connector.. disconnected from the harness) you get a clean sweep? 1.0 is what it should be at idle. Try running the car with it disconnected from the harness and see if it runs well.