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Listen to my hands...
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Discussion Starter #1
I finally had the chance to dyno the car with a wide band today. The results are scary :eek:

I did all the dyno prep things like reset the ecu etc...

The car put down 606rwhp/554trq. My A/F readings were: 5k 15.5/5.5k 18.0/6k 14.3/6.5k 14.5 all the way to 7.5k. No tuning with the AFC made any difference. I could not get it to budge any richer. The VPC was at 3 o'clock. The car was very rich until boost came on. Down in the 8s at idle to 4500 rpm. Most A/F graphs I see are just the opposite....lean then rich.

It's either the damn ECU, or the AFC and VPC are not wired together correctly...because nothing I did with the afc changed the fuel readings.

Anyone have a clue as to what could be wrong?

Thanks.


Scott

Peace

[ August 18, 2001: Message edited by: Scoop ]
 

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I would guess something must be wrong with the VPC. The first thing to check would be the pressure sensor I'd presume.

The manual states for following:

With the ignition key on, use the green wire as a ground. The yellow wire should be at 5 volts. The blue wire should be at about 1.744 volts with the hose disconnected from the pressure sensor. Check the voltage between the blue and green wires. It should be as follows:

kg/cm2 voltage
0.1 1.907
0.4 2.399
0.7 2.889
1.0 3.380
1.5 4.198
 

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Wow, I was under the impression that your engine would be toast with A/Fs like that.

Assuming the wideband is working right, there is another possibility. I've heard of people adding fuel (trying to compensate for leanness) while the ECU is still in closed-loop operation, in other words at low RPMs. This causes the ECU to take out fuel. If the ECU's long term fuel trim gets > 10%, it effect the WOT fuel trim (which is a fixed value throughout open-loop operation). So by adding fuel in closed-loop mode, you lean the car out in open-loop, where you would be boosting.

If the VPC isn't the culprit, you could find someone with a VPW OBD2 scanner and see whats going on with fuel trim and MAF voltage.
 

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Scoop,

Those AFs are absolutely #uck!ng INSANE! Check the pressure sensor for the VPC, and also check to make sure the boost hose to the fuel pressure regulator is intact.

It's amazing your motor hasn't grenaded yet. What sort of EGTs are you seeing?

I'd stay out of boost at all costs until this is fixed.

Also, try another '98 ECU. I think Jarrett sells them for $75 because they're kind of worthless and ppl are upgrading to the old ECU's.

BTW, it's interesting to note that I had a similar problem to yours, but it was when I ran w/ a 94 ECU. I had no control over AF's - the car always ran 13.5:1 on boost. And pinged. Not good. All the while others with 98's have run 94 ECU's for years w/o problems.

Regards,
Andi


Originally posted by Scoop:
<STRONG>I finally had the chance to dyno the car with a wide band today. The results are scary :eek:

I did all the dyno prep things like reset the ecu etc...

The car put down 606rwhp/554trq. My A/F readings were: 5k 15.5/5.5k 18.0/6k 14.3/6.5k 14.5 all the way to 7.5k. No tuning with the AFC made any difference. I could not get it to budge any richer. The VPC was at 3 o'clock. The car was very rich until boost came on. Down in the 8s at idle to 4500 rpm. Most A/F graphs I see are just the opposite....lean then rich.

It's either the damn ECU, or the AFC and VPC are not wired together correctly...because nothing I did with the afc changed the fuel readings.

Anyone have a clue as to what could be wrong?

Thanks.


Scott

Peace

[ August 18, 2001: Message edited by: Scoop ]</STRONG>
 

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Anyone have a clue as to what could be wrong?
Your car is a piece....

J/K

Just so everyone knows, Scott is running an OBD1 ECU with a G-Force upgrade.

Scott,

If you can catch me with some time I'd be more than happy to go over your wiring with you.

I don't think I need to echo what others have been saying. I'd stay out of boost for a bit until you get this figured out.

Let me know if you want to get together,

Howard
 

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Just going off what was posted it seems you have a handful of possibilities. One that stands out is the G-Force ECU... I too have noticed one running way to fat down low.If you do have one, get rid of it....the VPC needs to work with a stock ECU. (94 or 98 it shouldn't matter) I was also wondering what fuel pump you had and what fuel press regulator you were using. What were the settings and what is the rate of gain in relationship to boost. It kinda seems you go leaner as boost rises...it could be your fuel pressure at high boost is too high... this can cause your fuelpump to backup and not deliver the volume necessary. Your fuel pressure should be at 36lbs(2.5bar) above intake manifold pressure at all times. In other words at 10 lbs of boost fuel pressure is 46lbs, at 15 lbs boost fuel pressure should be at 51lbs. First I would get a stock ECU. Aren't these Supra's amazing...poorly tuned you can still muster 600+hp.... incredible!
 

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Don't rule out the Wide Band oxygen sensor as the cause either! When they go bad it normally hangs out in that general area of the fuel curve.It happens to me all the time at the shop! :)

crispeed
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just to add... if and when your A/F starts to read better numbers don't be concerned if there is a reduction in HP. Running lean produces hp but is not considered safe.And as Crispeed suggested it may be that sensor. Exhaust Temp. will help you determine that.
BTW... Crispeed, what are your thoughts on why those go out. Natural wear or maybe even dropping it on the ground a couple times??? Do you just clean it up a bit or do you have to get a new sensor?
 

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Listen to my hands...
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Discussion Starter #9
Thanks for the responses. The A/F sensor is fine. The guy running had his twin turbo Stang and 3 other cars hooked up to it. They were able to get great readings and tune their cars...actually improve their HP#s.

I have been trying to borrow an ECU to see if it would make a difference, but haven't been able to find one.

My car was one of the first to use the AFC/VPC combo. Apex-i gave us 2 sets of instructions to install. I don't know if it was installed correctly.

I'm not sure if it's a 98 just not liking the pre-OBD2 ECUs.

I know those ar dangerous A/F #s. I didn't go past 3.5 k on the way home.

I have had this setup for over a year now. It's really frustrating me not being able to pin point my bottle neck on fuel.

For the record, I'm running twin pumps and SX FP regulator.

Scott

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boost is good
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hey, i just got done wiring the vpc and afc..after about a million emails (thanx andi) i finally got it, heres how it goes.

cut the #66 wire. connect the yellow wire on the vpc to the white wire on the afc. then connect the yellow wire on the afc to the part of wire going into the ecu that you cut. you leave the other end of the wire dangling.

if you wanna read more in depth about it, go to http://groups.yahoo.com/group/mkiv/ and search for afc with vpc, all the posts should come up. good luck
 

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Originally posted by choritsu-shi:
<STRONG>just to add... if and when your A/F starts to read better numbers don't be concerned if there is a reduction in HP. Running lean produces hp but is not considered safe.And as Crispeed suggested it may be that sensor. Exhaust Temp. will help you determine that.
BTW... Crispeed, what are your thoughts on why those go out. Natural wear or maybe even dropping it on the ground a couple times??? Do you just clean it up a bit or do you have to get a new sensor?</STRONG>
From what we've been noticing is that the Borsche ones are very sensitive to moisture!
Hence with those we normally make a past without the sensor in position to remove as much moisture as possible from the vechicle.
The NGK sensors seem to tolerate this a lot more without any problems.Actually we've lost about 10 plus sensors on the dynojet and is yet to loose one from the Euego Wide band that use the NGK sensor.
Another common failure is due to heavy use of leaded race fuel. That shortens the life of the sensor also. Sometimes we can increase the life of the sensor after heavy leaded fuel use by cleaning it with butane gas.
Dynojet has taken great steps recently to correct the moisture problems with their sensors by the use of a much stronger vacum pump and remote sensor placement along with a much improved water seperation unit that should greatly improve the life of the sensor.

crispeed
87TII
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651RWHP/520RWTQ
2600lbs
 

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Originally posted by Scoop:
<STRONG>Thanks for the responses. The A/F sensor is fine. The guy running had his twin turbo Stang and 3 other cars hooked up to it. They were able to get great readings and tune their cars...actually improve their HP#s.

I have been trying to borrow an ECU to see if it would make a difference, but haven't been able to find one.

My car was one of the first to use the AFC/VPC combo. Apex-i gave us 2 sets of instructions to install. I don't know if it was installed correctly.

I'm not sure if it's a 98 just not liking the pre-OBD2 ECUs.

I know those ar dangerous A/F #s. I didn't go past 3.5 k on the way home.

I have had this setup for over a year now. It's really frustrating me not being able to pin point my bottle neck on fuel.

For the record, I'm running twin pumps and SX FP regulator.

Scott

Peace</STRONG>
Oh your running the APEX-i AFC...I was thinking the HKS AFR...hmmm....I know a lot of guys use the AFC-R with the VPC and as you stated, even APEX-i gave you 2 sets of instructions...(yeah been there done that too)...Personally I feel those 2 units used together makes no sense. They both alter the input signal before reaching the ECU yet both need the original signal to alter first.So if you wire the VPC first then the signal the AFC-R recieves is what the VPC has already changed, and vice versa. Just try the VPC by itself, after you get a stock ECU.(98 or 94 ECU the vpc works with either)... you'll see. But first what is your actual fuel pressure at the rpm points?
Crispeed, thanks, that's good info...
 
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I would say eliminate as many variables as you can. Make sure the VPC is installed correctly, and set to zero across. Unwire the AFC. Put a borrowed stock ECU in there. You should run correctly just like that. While 14.5 is near perfect for a NA motor, you want around 12.0:1 tuned on the dyno for safety under load on the road. The extra fuel provides cooling. I bet with the above setup, you would get like 10:1, and the opposite in pattern like you said. Work from a clean slate.
 

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Originally posted by gritsak:
<STRONG>hey, i just got done wiring the vpc and afc..after about a million emails (thanx andi) i finally got it, heres how it goes.

cut the #66 wire. connect the yellow wire on the vpc to the white wire on the afc. then connect the yellow wire on the afc to the part of wire going into the ecu that you cut. you leave the other end of the wire dangling.

if you wanna read more in depth about it, go to http://groups.yahoo.com/group/mkiv/ and search for afc with vpc, all the posts should come up. good luck</STRONG>
Is this the yellow wire coming from the engine bay on the VPC? IF so which end do u connect to? the one going to the unit or back to the engine?
 

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Listen to my hands...
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Discussion Starter #17
Originally posted by Andi:
[QB]Scoop,

Those AFs are absolutely #uck!ng INSANE! Check the pressure sensor for the VPC, and also check to make sure the boost hose to the fuel pressure regulator is intact.

It's amazing your motor hasn't grenaded yet. What sort of EGTs are you seeing?

I'd stay out of boost at all costs until this is fixed.

Also, try another '98 ECU. I think Jarrett sells them for $75 because they're kind of worthless and ppl are upgrading to the old ECU's.

BTW, it's interesting to note that I had a similar problem to yours, but it was when I ran w/ a 94 ECU. I had no control over AF's - the car always ran 13.5:1 on boost. And pinged. Not good. All the while others with 98's have run 94 ECU's for years w/o problems.

Regards,
Andi


I would try another 98 ecu, but I need to the extra revs for the Twins.

Scott

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boost is good
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Originally posted by Silver Orchid SP60:
<STRONG>Is this the yellow wire coming from the engine bay on the VPC? IF so which end do u connect to? the one going to the unit or back to the engine?</STRONG>
im kinda unclear on what your asking, but ill try and answer. i dont think the end of the wire going out to the engine bay get connected(since the MAF is unplugged anyway) you just cut the #66 wire on the ecu as far up as you can get, i did around 3 inches from the ecu. then connect the yellow wire on the vpc into the white wire on the afc. then connect the yellow wire on the afc to the end on the wire you cut thats going into the ecu, and the other end of the wire going to the engine bay gets left unhooked to anything. does this answer your question any?
ide double check with someone else first though before you do anything becuase i just learned this a few days ago and i could be mistaken
 

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Andy,

Those directions are dead on as far as I know.

The wire your leaving unattached is the wire leading to the old MAF sensor.

Basically you VPC replaces your MAF. So your going to wire the AFC with that in mind. The AFC actually intercepts your "air meter" signal and alters it to trick the ECU. Wiether your air meter is the MAF, or the VPC.

AFC wiring other wise is the same. Keep in mind that the Apexi directions are NOT correct. They say to cut into the preasure sensor wire. This is wrong. I did some research on this when I was doing my AFC install. The MAF is the sensor that the ECU used to determine how much fuel to add. It is primamry. The Preasure sensor is used to detect boost (for boost cut), and is used as a back up for the MAF if it should go into limp mode (when you blow your IC hose, and unplug the MAF to drive home)

mkiv.com has a complete article on the install/setup.
http://www.mkiv.com/techarticles/afc/index.html

BTW, we may have Scoops problem (or part of it) figured out. We'll let you know in a few days when we have time to go over the car.

Later,

Howard
 

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This may be a stupid question given your turbo setup, but do run a high flow catalytic convertor? I know several guys who have tried to use the wide band 02 sensor (when placed in the tail pipe) and since they had a catalytic convertor in place they thought they were running very lean. Just a thought.

Later, Steve
 
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