S5 Tii Fuel Cut Hackjob and weird decel issue
 

The title says it all. I've searched and searched, read the fsm over 5 times and I still cannot figure out for the life of me what the answer is.

Dilemma:
Purchased s5 tII. Runs great accept for chugging on deceleration and light throttle (which I will chalk up to the trouble code 10 and a need for the tps to be adjusted). If so, error code 10 is in regards to the air intake thermosensor built into the MAF. Is there anyway of replacing this without a new maf? Kind of a stupid question I guess.

More concerning:
This vehicle is equipped functioning gauges ( fuel pressure/boost/water temp) and when I hit boost and the gauge indicates a spike to 12 psi. I am not hitting fuel cut. Is there a hack method of making this happen? The reason I ask is that I have searched the car twice over and can not find a FCD. I have also cracked open the ECU and it has not been modified. However, there are a few wires grounded from the harness near the ecu and on on the ecu itself.

Basically, is it this aforementioned hacked up ecu wiring that could allow me to bypass fuel cut? I am not too happy about it as I have seen some high spikes in boost pressure.

Here is a pic of the ecu/wiring.

Um link to eBay patch harness? This is one satch will answer I'm sure, but which plug/pins are grounded?

The temp sensor within the AFM cannot be replaced on an S5. Make sure the connection to the AFM plug is good (make sure the plug is clean and none of the wires within the plug are pulled back in the plug and not mating w/the pins to the AFM) and if the error code persists then the AFM needs replacing. There should be a resistance test in the FSM's emission and control section to test the sensor as well.

What are the colors of the wires which are grounded related to the ECU?

Sorry about not including the picture. I thought I deleted the last statement and was going to add it today.
Thanks for the input on the sensor. I will double check that and set the tps today and see if that helps at all.

The wires are not off the actual ecu as it turns out, they are off a plug that connects down by the ECU though.

Colors are both black/yellow. When looking at the connector, from right to left looks like pin 1 and 4. I could have this backwards as well as I am not sure what plug this is.

http://s13.postimg.org/bzyeh76sn/ecuwiring1.jpg
http://s13.postimg.org/8f2ixz293/ecuwiring2.jpg
http://s13.postimg.org/3vqacgkdj/ecuwiring3.jpg

This last picture shows another wire being grounded. I still need to trace it up the loom because despite all the bad wiring, the previous owner wrapped it all up and hid it well.
http://s13.postimg.org/7o9ss6zvr/ecuwiring4.jpg

not sure about s5 but my s4 those are grounds. he may have been having the usual grounding issues and decided this is how to fix it.

The connector is for the anti lock brake system and the two Black wires are grounds.

Thanks for the quick responses guys. Is there any other way of cheating fuel cut? I still cannot locate an FCD. So unless my electronic boost gauge is reading off, I am not sure what is going on.

As for the Decel issue, I have a friend that has a spare MAF so we shall test that out and see if that cures the problem. It is odd as the CEL only comes on under acceleration but it hesitates on deceleration.

TPS was adjusted accordingly yesterday and the issue persists.

Your TPS has two aspects to it so both readings are important (full range and short range). You could also unplug the sensor to see if that changes things. Your boost sensor might be problematic. The FSM will show the voltage for the output wire and what the resistance test should show.

Does the stock gauge work? You'll have to check the signal from the boost sensor at the ecu. Take a look at page z-42 of the wiring for pin location and specs.

As for the TPS, I did check both ranges on a DMM and they were adjusted accordingly. It seems that the stock boost gauge does not work. I am thinking the previous owner may have spliced into the boost sensor to trick it some how.

Will be testing a different maf today.

To check the TPS requires more than to see if it reads properly at idle. You need to make sure the voltage reads properly as the throttle opens up. The voltage on the G/R wire, narrow range, should go from 1 volt to 4.5 volts and there should be no bumps but rather a smooth transition from low to high. Full range, Black/Green wire should read from .8 at idle to 4.3 volts full throttle. A DMM cannot really do this but an analog meter will be more effective. Again, unplugging the sensor might lead to some insight.

The boost sensor is located at pin 2H of the ECU. Wire color is Green/Yellow and should read from 2.2 to 2.5 volts w/key to on. This reading can also be taken from the sensor plug itself when the sensor is not unplugged.

Is the car a true TII or a turbo swap?

The car is a true TII. I swapped in another MAF sensor and the problem persists. Unplugged the TPS and the problem still persists. Only change is the CEL is on all the time. I may just go ahead and replace the TPS anyway.

Any other insight into this? What would cause the CEL to come on only under acceleration?

you know you can pull the codes on that S5 since it has a CEL.
also there is another AIT on the throttle body inlet..It could have a bad connection.That connector is not exactly a tight fitting thing.

As mentioned in the OP, I pulled a check code 10. This indicates that is an intake air thermosensor in the MAF. However, I replaced with a semi newer unit and it still persists. I doubt both MAF air sensors would be bad. I did clear the code and try driving but it came right back on.

The car idles like it is streetported, although I am positive it is not.

You could have a poor connection at the plug. So, make sure the wire for the sensor is not pulled back within the plug. You can look in the FSM and find the pinout for the ECU either in the emission and control section or the wiring diagram. It will list the expected values of each pin and the intake sensor in the AFM is one of them.

The pins seemed alright, but I will check the resistance tonight. However,the car needs to be at operating temperature correct? Thanks for the help Satch.

On another note. The car is a true TII but it had a motor swapped in. How can you tell if it is a jdm swap besides the intercooler? The intercooler says Rotary powered with Intercooler but that could have just been swapped for a "jdm" factor.

It may be worth noting that the car has a blitz blow off valve as well. I am going to remove that and block it off to see if it is a source of vacuum leaks.

It wont help but for what its worth my Tii(real 89 tii) never did the overboost fuel cut and I have no idea why. The boost gauge(factory) was acting up and I thought it was the map sensor, replaced it, the ecu and the VAF and the problem persisted. I eventually installed a stg2 rtek and can now verify both maps sensors are indeed good. No idea why, but never cared after putting the rtek in.

I have an 87 TII. Ive seen spikes at least 12 and never had fuel cut on stock car.. thought it was kinda weird.

^ stock car hitting 12lbs? odd

Update:
Found out that the O2 sensor wire was broken off, so I replaced that, checked the TPS again, checked the connections to the MAF. All to no avail. Car still hesitates on deceleration and backfires as well.

Checked for Vacuum leaks to no avail.

Check engine light still comes on under load and goes off when you let off the throttle.

I am at a loss.

How did you check the TPS? Have you checked the ECU pin for the intake temp sensor to see what it reads? You stated the wire to the oxygen sensor was broken. This by itself should have thrown an error code. That sensor should have a sheath surrounding the wire which is a ground. What was its condition.

^ I checked the TPS using a better quality DMM. Unfortunatley, as you stated, it still isn't accurate enough to sweep for dead spots. I am just going to order a new one tonight.

The o2 sensor wire was broken off the actual sensor itself, so it was replaced with a new unit.

I checked the voltage at the pin 2k off the ECU (air intake thermosensor), and it checked out within the FSM specs.

UPDATE:
I plugged in a friends spare turbo ECU, cleared codes, and tested for CEL's again. This time I am getting a ton of them. I will post a video for help deciphering once it uploads. If I counted correctly, at least 4 of these errors are related to emissions equipment that was removed that I am not concerned with.

Video

<iframe src="//player.vimeo.com/video/112599576" width="500" height="281" frameborder="0" webkitallowfullscreen mozallowfullscreen allowfullscreen></iframe> <p><a href="http://vimeo.com/112599576">ECU Codes</a> from <a href="http://vimeo.com/user34722652">Dalas</a> on <a href="https://vimeo.com">Vimeo</a>.</p>

The codes that I think I am reading are:
12-Throttle sensor
25
30
31
32
33
38
42

25-42 codes would be in regards to the emissions equipment that has been removed.

So I purchased a brand new TPS Sensor and installed. Slightly better idle and less hesitation but it still does the same thing and pulls codes 12 and 25.

I am at my wits end with this. I have adjusted idle, installed NEW tps sensor, cleared the codes, and I still get these errors.