'89 GTUs NA dyno, with RB long header

Okay, the car is a stock-rebuild S5 NA with less than 3K miles on it. Car has been showing a CEL with Code 17, replaced the O2 (cheap-o Bosch universal, now I know not to do that, ordered the NGK/NTK), need to run a direct wire from the sensor to the ECU. Car behaves like it is in limp mode, but probably really isnt. Bucks at 3-3.8Krpm, no power anywhere, and occasionally acts like it is fuel starving-- studdering, loss of power even more so than before, sometimes dying altogether. Fuel mileage is 9-15mpg no matter what, even on a long trip at low speeds through the central valley up to a race.

HKS CARB-legal intake
Custom short-tube header with cat, 2.5" single-exit high flow exhaust
New NGK wires/plugs, aux grounds on engine and key parts
Mazdaspeed alt and crank pullies
Very good/high compression
Stock S5 ECU

On this particular dyno pull we put the long-tube Racing Beat header on there and deleted the cat.....with the above settings we only got 97-98hp and 100-101ft-lb torque, with massive misfire and cutout up top, and take a look at the AFR.

I need help! The car is up in Merced/Atwater in storage until the ProSolo race this coming weekend (didn't want to drive it back and forth), I can take parts and tools up there to get it semi-sorted out before the Pro.

Thanks!

-JamesW
SCCA Solo2 STS2-class
San Diego National Tour winner
Fontana ProSolo winner
All on <100hp!

 

Far as I know, if you are in limp mode, the CEL will illuminate on the Dash.

 

Do you have pictures of the intake?

 

The intake is just the HKS green foam filter and adapter plastic and a CARB sticker. No heat shield, nothing special.

 

Run that wire...it should fix it right up!

That is what I had to do to fix my Code 17 on my S5 TII

 

Pull error codes from the S5 ECU?
Those things have codes for almost anything, so check that first.

If that doesn't show anything, go for all the basics...
Spec ignition timing - hell, run some advance if it's legal
Check fuel pressure at rails
Check spark plugs
Check for arcing
Check double throttle not sticking closed?


-Ted

 

RETed--

Always showing Code 17.....we've had to disconnect the battery before every lap just to make sure it's cleared out. I am brining wire and connectors up to Atwater on Friday to try to make a fix before the ProSolo. I need to bring a timing light up as well, it is set about dead in the middle of the sensor, but I have not read it off of the pulley myself since it left PureSports. Plugs are new, will bring another set....they have been fouled in the past, as the car is running waaay rich. New NGK wires, no arcing, have checked it in the dark. Double throttle not sticking, but occasionally one of the 6-port actuators will stick OPEN after a run. All of our dyno sessions have shown the 6-ports to open fully.

Thanks for the replies, keep them coming....I am heading up Friday with a list of things to try....the more the better, I will be away from a computer after Friday morning!

-JW

 

Ok, that's the O2 sensor - this should not affect WOT power.


You mean in between the two marks?
If so, you're running about 7 degrees retarded.


Are you running the stock fuel pump?
Or are you running some kinda upgrade fuel pump?
Change it back to the stock fuel pump, or at least jack the fuel down (I doubt this is legal) with some kinda fuel controller.

Else, FPR might be on the fritz and causing higher than normal fuel pressure...

Else, also check the specs on the air temp sensor and the water temp sensor (resistances).
Sometimes the sensors can be out-of-spec and cause all kinds of weirdness (especially ragged AFR's), but not trigger an ECU fault code...


-Ted

 

I didn't think of those sensors.....I will check them. I don't have the Mazda factory manual, can someone post the resistance values for each? I may pick up new sensors either way and take them up to the car, it is too important to waste another weekend.

 

Or do you mean you just stabbed the crank angle sensor, and placed the securing bolt in the center of the adjustment slide??

Better check that with a timing light..

 

I didn't install the engine or tune it/set it up, so I am kind of working blindly. I never saw a timing light get used on it, it doesn't mean that it wasn't set. The crank angle/"distributor", as I recall (the car is not here), was set roughly midway on its adjustment arc.

With the Mazdaspeed/Racing Beat underdrive dual main pulley, what are the marks at? Just like stock? What is the recommended timing for spirited/performance driving with stock plugs?

Bringing a crap load of parts up tomorrow to try to get this thing running.....

-JW

 

Code 17 caused my s5 tii to run like dog squeeze.

James

 

Replaced the wire to the O2 and put an NGK/NTK sensor in there, and replaced the gross plugs....car ran great! Not enough for a ProSolo win, as the car does not seem to like concrete at all....time for more testing. Thanks everyone, and I will try to post a new dyno sheet with the car running "correctly".

 

does the stock ecu use the o2 readings at all at wot?

 

Recently tried to get the car to pass the state's emissions testing, barely failed on HC only. Discovered also that the timing may have been severely retarded.....pulled the CAS and rotated it a position over (to the next mark), car ran much better overall but has a terrible idle. Tried to put it back, car felt flat and even cuts out at ~6500rpm again. So now I'm stuck with a really shakey idle, but fantastic pull midrange and up top. Car does not run hot, and does not smell really rich anymore.

One thing we did find also was that touching/moving the wiring harness from the MAP sensor changed idle quality, we will open up the loom and check the wiring for breaks/melts/etc. No change at all if you unplug the MAP sensor.

Another dyno session to follow. PureSports did my other dyno, they burned down.....finding a new place to baseline while our dyno is on order.

-JW