3.6 conversion idle problem/ECU help

[ssfrancis]

Thanks for any advise in advance- I've been trying to figure this out for a while and I could use some help.

Background:
95 993 3.6 swapped into a 74 911
Originally a tiptronic engine
Cintex chip
Older Patrick motorsports wiring kit

Problem:
I installed the engine and have had this problem from day 1. With the ISV plugged in the car idles anywhere from 2k -3k rpm. After DME reset it will start fine, idle around 1200, then clime to 2-3k rpm and remain. After warmed up it will idle fine with the ISV not plugged in, there is very little hunting but I don't have a massive vacuum leak that I can find (lots of time searching with starter fluid and smoke)
-I replaced the ISV with a brand new one, no change ($$).
-TPS seems to be working within tolerance.
-Throttle is returning to closed fine
-Ive gone through the DME plug, all looks normal.
-SAI removed, but that was after the problem had begun.
-I wired the check engine light (ground from pin 8 on T-16 plug) and so far I get nothing (which seems strange because I have a chip?).

A couple questions:
1- When all sensors are plugged in I get a loud hum from the engine. With out the ISV plugged in I do not. Is that normal?
2- Could it be the chip or DME?
3- Any other suggestions? I'm stumped and would really like to have a car that idled cold and so would my neighbors

[Chuck.H]

Have you plugged in an OBD_II code reader to see if there are any stored codes?

Have you put a volt meter or oscilloscope on the ISV wires to the DME while the car is running? Perhaps one of them is shorted in your wiring harness and holding the ISV open?

Keep us posted on what you find,
Chuck.H
'89 TurboLookTarga, 391k miles

[ssfrancis]

Hi Chuck,
It's an OBD-I engine. I did wire the check engine light but it is either not working properly or not throwing any codes.

I have not checked the ISV voltage, good idea. Is it supposed to be around 9 volts?
Sadly I do not have access to a O-scope, but could. What would I look for?

thanks
-s

[ischmitz]

A couple of pointers:

- any chip where the ckecksum has been calculated correctly will NOT throw a CEL.
- the CEL needs to be on when you turn the ignition to RUN without starting the engine. If not you didn't wire it correctly. Remember the DME supplies GND when it wants to turn the light on. The other side of the bulb needs to be connected to permanent +12V.
- the CEL can be used to "flash out" DME failure codes in the absence of a Hammer, PST-2 or similar - pretty useful.
- if the engine came out of a tip or manual doesn't matter. Chances are the Cyntex chip has all pointers bent to look at the manual maps only. In addition you should make sure the harness has the correct version coding. It tells the DME whether to be a tip or manual version.

With regards to the idle issue can you make sure the engine dies when you plug the ICV intake. If not then something is seriously wrong. Think of the ICV as a variable bypass of metered air. In other words it acts similar as if you would crack the throttle plate open ever so slightly. That being said the throttle plate stop has to be set in such a way that the engine idles at 880 RPM with the ICV in its mid-point. That will allow the ICV to influence idle in either direction to make sure it'll stay around 880.

In you description is wasn't clear whether the engine idles fine with the IVC port on the intake downstream from the throttle plate being open to the atmosphere or being plugged.

Next, as yours is a transplant have you made sure to properly deal with the vacuum plumbing normally intended for the brake booster? It needs to be plugged, else it acts like a giant leak.

A tester will allow you to read out what the ICV commanded position is. In addition to that you need to make sure the ICV driver is working so that the ICV actually moves. The output is not a constant but a duty-cycle modulated pulse train. So you need an oscilloscope to properly test. Or a tester that actuates the ICV against its stops.

Regards,
Ingo

[ssfrancis]

Ingo, Thanks so much for your reply.
To address your points:
- I have not plugged the ICV down stream of the butterfly. If I unplug it when the engine has been warmed it will idle fine. I will try to plug it tonight and see if I can get it to run.
- I have little doubt the ICV is moving, the slow increase to 3k RPM must be from the ICV opening... at least I can see what else is raising the idle so high.

- All vacuum ports have been plugged (brake booster included) with smoke and starter fluid I can find no leaks.

I'll try to borrow an o-scope to get a reading.... but what should I look for to be in spec?

thanks again!

[PcarPhil]

Here are a few thoughts after I recently was having idle troubles with my OBD1 3.6 VRam engine:

1. How old is the Cyntex chip? If it's an older chip it may be defective. There was a bad batch of chips years ago, some of which are still in use. They cause all sorts of issues including high idle. If you don't know the history of the chip I'd consider swapping the chip for a different chip (stock, Steve Wong, new Cyntex, whatever).

2. Have you performed an idle adaptation after leaving the battery disconnected for 24+ hours? Another way of doing the idle adaptation is simply let the car idle for 20 minutes or so after getting the car up to temp, although I've had better luck with Steve Wong's version in the link.

3. If you haven't cleaned the ISV I suggest doing so. A clean ISV is more responsive vs. a dirty ISV. Also do a search on making the ISV adjustable. While the DME actually controls the ISV you can manipulate the open/close point within the ISV to help fine tune the idle.

4. My DME seems very sensitive to voltages. I have a parasitic drain on my battery when the car is off due to the window relay staying energized. If I don't leave a battery tender hooked up then after a few days the DME seems to lose the idle adaptation (or it makes the engine idle high to help charge the battery). I haven't quite figured this situation out (need to eliminate the parasitic drain) although keeping the battery in proper order seems to take care of this issue. In other words - if your battery voltage is low you may be chasing an idle problem due to the low battery.

To summarize - with my car cleaning the ISV, performing Wong's idle adaptation, keeping the battery charged, and verifying no vacuum leaks has produced an acceptable idle.

[Chuck.H]

Oops sorry thought they had OBD-II by then, my bad. I shouldn't even be responding, as I'm only familiar with the engines I own :-) Ingo's advice is good, the CEL should still come on when the power is first applied to verify it's working.

On some ISV's they are controlled by square wave signals, essentially a 'duty cycle' of on and off, which causes the ISV to flutter around a certain opening. If this is the case here, then you can clearly see this duty cycle with an O-scope, and see it fluxuate as the throttle is opened and closed if all is correct.

Have you considered you have some other sensor failure that is causing a 'limp mode'? Many ECM's will raise the idle in limp mode.

Hope this helps, sorry for Porsche's I only have 3.2.
Chuck.H
'89 TurboLookTarga, 391k miles

[Bill Verburg]

Couple of possibilities
1) the chip try another, Ingo's No Bad Days and 911Chips might be good choices
2) the DME for a tip is different from a manual. The tip DME gets a signal at pin42 of the DME from the gear selector. In P and N the the control is connected to ground, In any gear the ground is interrupted, this is supposed to lower the idle rpm from 800 to 750. There is also a meshing signal at pin 51, the signal comes from the transmission when it changes gears, this signal is supposed to retard the timing a tad to ease the shift.
3) to do adaption all you need to do is disconnect the battery for a minute or so. Then restart w/o touching the gas pedal, this sets the throttle base position, let the engine idle for 15-20 min. It doesn't hurt to redo this.

[Bill Verburg]

Forgot to add the other Tip specific pins in the DME, these are unused in a manual
42 tip stepping switch -I'm not surr what this does
44 tip coding tells the DME that it's a tip
52 PWM(throttle position sensor) a manual uses pin 52 which is the signal from the throttle pot.

[ssfrancis]

Thanks for all the suggestions. A little update:

1)Preformed the idle adaptation. No change.

2) Will not idle with the ICV plugged.
I plugged the ICV on the engine side and it will not idle cold. I let it warm up. Plugged it again and it will not idle.

3) I'm reading 12.3 volts at the ICV middle pin. I though it was supposed to be lower?

4) I removed pin 44 from the DME- No change

5) The humming noise I mentioned earlier is the ICV, it is vibrating to the touch. Both the old ICV one and new ICV do it when plugged in. Is this normal?

6) I'm reading 14.2 volts when running at the DME. Ground seems good.

7) CEL is wired correctly as ground to +12v source. I have it to the green and grey wire on pin 8 of the T-16... sound right?

I'm beginning to suspect the Cintex chip. Anyone have a stock 993 chip to lend out?
A new NBD or Wong chip is just too much money to buy just to try.

Any other thoughts?

[Bill Verburg]

The ICV shouldn't be noisy in operation, if you have it in you hand you can make the flapper slap against the stops

The ICV is just a twin coil positioner, the DME(stock chip) asks for an 800rpm idle hot 1100rpm cold

The positioner is supplied w/ 2 clocked electrical inputs from the DME, pin 4 is + to open, pin48 is grd, pin 49 is + to close

This creates opposed torsional forces on the armature. Due to the intertia of the armature the positioner adjusts itself to a particular angle that corresponds to the pulse/duty factor of the signal received

By modifying the input signals when the engine speed changes, the pulse duty/ factor of the signal supplied to the positioner changes as well. Th programmed nominal rpm is compared to the actual measured rpm . The air flow is then modified by the positioner until the nominal rpm and actual rpm are within the defined rpm envelope.

when you look at the plug at the ICV the center terminal is battery voltage, the Left and Right are the + duty cycle signals which will vary from 0 to battery voltage but they will be opposite each other so the signal across them should be from +battery V to - battery voltage, ie -13v to +13v, an oscilloscope will show a square wave ~5ms wide, -13v to +13v

There should be a slight audible pulse.

Another possibility is some other fault in the DME, we are seeing more and more degradation of the solder connections and plastic parts in the DMEs, these will require a rebuild, ECU doctor in Fla is very good.

[mysocal911]

Originally Posted by Bill Verburg

The positioner is supplied w/ 2 clocked electrical inputs from the DME, pin 4 is + to open, pin48 is grd, pin 49 is + to close

If this '95 993 is using the 55 pin DME then the above is not totally correct. Yes, pin 4
is the open signal, but pins 48/49 are the reference signal pins from the speed sensor.
The close air valve pin is pin 22. The center pin to the valve is 12 volts.

[Bill Verburg]

Originally Posted by mysocal911

If this '95 993 is using the 55 pin DME then the above is not totally correct. Yes, pin 4
is the open signal, but pins 48/49 are the reference signal pins from the speed sensor.
The close air valve pin is pin 22. The center pin to the valve is 12 volts.

My bad I had that mislabeled on my pin map and didn't look at the other pins
pin 4 is idle open
pin 22 is idle close

the center pin is battery voltage it is energized from pin 37 which also energizes terminal 87 of the DME relay and the resonance shift flap terminal 2

Pin 48 & 49 are engine speed sensor

[ssfrancis]

So I started digging into my harness to look for shorts.... And I found this (pictured)
It's some kind of transformer coming off of pin 4 on the t16 plug. Goes to purple and black on the dme side.
Car will not start with out it plugged in
Thoughts???


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[ssfrancis]

Scratch that, it is for the tach. Not sure why though....

[ssfrancis]

Finally took the ecu out. Nothing obviously cracked.... But this strange.
Normal?



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[ssfrancis]

Attachment problem:


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[ssfrancis]

Next question. What chip is this?


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[ischmitz]

Not sure what you refer to as "strange". The white stuff is glue to support the resistor and normal. It's applied to reduce vibration impact causing stress fractures in the solder.

The second picture shows the aftermarket EPROM (aka: chip) with the paper label in the 28-pin DIP socket.

[PcarPhil]

That looks like a FVD chip, not Cyntex.

FVD, Porsche Tuning, Motorsport, Accessories, Motortuning, Sportfahrwerk, Felgen, Bremsen, Leistungssteigerung, Boxster, Carrera, Turbo