Replaced CIS Gaskets/Rubber... Now Cold Start/Running and Bucking Issues
 

Long post so bear with me here. Completely stumped as to what the problem is so hoping the Pelican brain trust can fish me out here. Big thanks to boyt911sc, Moozak, and timmy2 for all the help so far.

I am having cold start/running issues and a bucking at 2200 RPM regardless of engine temperature. Car runs great when warm otherwise!

Issue 1: Car starts cold but idle is very low and will stall if I don't give it gas. Under load when cold, bucks and sometimes small intake pop under 2000 RPM. Seems to 'pick up' and surges to 3000 RPM after that.

Issue 2: Runs great when warm except for a buck at 2200 RPM when under load, regardless of gear or speed.

A month back, I had a big CIS airleak in my USA 1980 SC. I replaced all the intake gaskets and CIS rubber but my car still won't run as well as it did before the whole incident.

Here's the original thread: http://forums.pelicanparts.com/porsche-911-technical-forum/806211-sudden-bucking-sputtering-highway-80-sc.html

Here's what I've done:

1. Replaced CIS airbox, gaskets, and rubber
2. Replaced fuel pump and filter
3. Set timing to 5* BTDC with vac line disconnected at 950 RPM idle
4. Set AFM plunger plate rest position to spec
5. Set CO to 3.0 (NOT the 0.8 recommended by Bentley) as per general forum consensus. Bucking was actually worse when the CO was at the spec 0.8
6. Verified AAR is open (1/3 open in freezer test) and closed (fully closed after oven test)
7. Tested injectors: 5 sprayed a nice mist while the 6th was slightly 'streamy'
8. WUR FP tested in spec, BUT, resistance when cold is double the spec at 48 ohms! However, this should only theoretically affect how long it is in 'warm-up' for, correct?

Fuel pressures are all within Bentley spec, as follows:

Cold = 26 psi/1.8 bar
System = 68 psi/4.7 bar

With WUR plugged in:
30 sec = 28 psi
1 min = 32 psi
2 min = 36 psi
3 min = 40 psi
4 min = 42 psi
5 min = 50 psi
6 min+ = 52 psi

Residual:
Starting = 32 psi
4 min = 26 psi
7 min = 24 psi
10 min = 22 psi
15 min = 21 psi
30 min = 18 psi

Thoughts:
1. Would the single slightly streamy injector cause the 2200 RPM bucking?
2. Completely stumped as to what the cause of the cold start/running issue could be... WUR bad? But as the FP shows, it's within spec...

Thanks Pelican! Been a great learning journey here but now I'm completely lost as to what could be the issues here... So close to having a great running car so I'm not quite ready to throw in the towel yet!

This has probably been covered by you but if the O2 sensor fuse is blown, you can replace the O2 relay till the cows come home. No juice to the relay. It will run like crap.

Also, if fuse is ok, pull the 12 pin connector apart at the "rear" of the engine compartment, (towards the front) To the right of the left shock mount. That is where the feed to the frequency valve passes through.

Eyeball those connections for crud.

A bad injector could be making one cylinder drop out. Setting co at .8 is leaner than 3.0 so that makes sense.

What about the plastic sleeves in the manifold tubes? New sleeves with new o-rings? New o-rings on the injectors? New manifold to head gaskets?

I think you know some air leak is there.

I agree WUR seems to be ok

Bob - when cold, the O2 system is in open loop so the system wouldn't even do anything then and shouldn't be contributing to the poor cold running performance??

I have replaced all those gaskets and confirmed no leaks in those areas via the soapy water test.

As well, I have engine vacuum of 16 in/hg when warm at idle. Within Bentley's spec of 15-22.

The system always runs in open loop when cold.

Have you verified the frequency valve is working in cold/open loop?

The frequency valve does not crank out a default duty cycle if no juice is supplied to it.

It needs power.

PS: I can help you find if your freq valve is working with engine off if interested,

Wur-072.........
 

Kenneth,

Your WUR-072 is out of spec. 48 Ohms is not the correct heater resistance for your WUR. Were the pressure tests done with a running engine or just the FP running? Please do this test for me:
1). Record the resistance (Ohms) of the WUR at cold condition.
2). Begin the control fuel pressure versus time tests.
3). Without interrupting the test, check the resistance reading by unplugging the electrical plug to WUR and use a multi-tester to read the resistance (Ohms).

I like to know the value of the initial resistance before start (cold) and after 3 and 6 mins. of run. During the test run, place your hand on the FV and feel the vibration if any. Keep us posted.

Tony

Ah, good to know. Well my interior dome lights work, so at least the fuse is okay... Check your PMs :)

The one thing I was unsure of is the frequency valve. Put my hand on it when warm and running and didn't feel a "buzzing".

Got the PM. It's 11:38 PM and I am tired. I will post how to "buzz" the freq valve without engine running tomorrow. Sorry. Out of gas.

Plus the babes are clustering. Cripes I need a break.http://forums.pelicanparts.com/suppo...leys/freak.gif

I dug around and think I found that old post of yours in regards to testing the FV with engine off (http://forums.pelicanparts.com/6816107-post29.html)

Unplugged the AFM, key to ON, and with the FP running, I checked to see if the FV was buzzing/pulsing.

... It sort of pulses? How loud/apparent should this buzzing be? I'm led to believe the pulsing is actually from my fuel pump rather than the FV because it was so faint! The CDI box hum was infinitely louder in comparison!

Just remembered another thing, as my car runs and idles perfectly when warm, I pulled the O2 relay under the passenger seat, and, no change whatsoever in idle. Ran like a top still. Talking to myself here but I think I know where to start looking...

Tony and Bob have the right ideas on where to start.

A couple of things occurred to me to put on the list of things to look at. Here is the attack plan: I would verify the WUR stuff via Tony and verify the O2 sensor is working first as Bob said. Next would be to look at injectors for fuel flow and check o-rings and sleeves. Throw a can of BG44k or Techron in the gas tank and see if that helps. If you have an injector that is clogging that might loosen some crud up. From there I would pull the plugs and see if you have any obvious differences between cylinders. If none of that turns up anything I would look at the distributor. Since you're saying the miss occurs at the same RPM range it makes me wonder if the mechanical advance on the distributor might be sticking. Not sure that theory matches up with your cold start symptoms though.

To make the Frequency Valve (FV) "buzz" all you need to do is turn key on, remove air box lid, slightly lift up air sensor plate arm. It should immediately buzz.

The arm needs a very small lift for this to occur. Lifting more will begin to activate fuel flow to the injectors. This sounds like a "weeeeeeep" type noise.

Cooper

Cooper is correct. The O2 relay is fed directly from the #30 pin off the fuel pump relay. I am thinking this voltage triggers the electromagnet in the O2 relay?

What would happen if you unplugged the relay and lifted the sensor plate? The O2 relay energizing is on the same circuit as the fuel pump but they are not dependent on each other to operate.

FV operation........
 

Bob,

If you unplugged the FV relay (don't know why it is referred as OXS relay), you have isolated and removed the FV from the circuit. Lifting the air flow metering arm would mean activating the FP (with the ignition switch @ ON position). The FV relay's coil is energized @ terminal #86 by the power coming from terminal #30 (FP relay). The FV relay is dependent on two (2) power sources:
a). FP relay terminal #30
b). Fuse #18

Both power sources should be present otherwise FV relay would not operate or run as designed. Here is the summary:

The main power source for the FV relay is coming from fuse #18. But FV relay terminals #30 and 87/87 are NO (normally closed) meaning the switch is OPEN (no continuity). When the FP relay is energized at terminal #30 power is sent to FV terminal #86, subsequently energizing the FV relay coil causing the switch to close. Power from fuse #18 is then connected to terminals 87 & 87a. Hence the FV gets power by these sequence of power switching.

Tony

Thanks Tony.

I did look at the electrical diagram in the Tech Info pages and thought the same thing as you stated regarding freq valve. However, as soon as I act like I know what I am talking about, my foot can end up in my mouth. Hence, the question mark.

OK, the fuel pump can run without the freq valve running. Wonder what that sounds like when you lift the air sensor? If you lift it a wee bit you can hear the buzzing - very pronounced. If you lift it higher, there is a squealing noise also which I think is fuel movement. Maybe at the injector pintles?

So I am thinking that Skunk could hear the squealing even if the freq valve was not energized when lifting the plate.

All I am interested in is helping him confirm the freq valve is working.

Bob, checked now per lifting the AFM a wee bit with ignition on, there is NO buzzing from the FV.

What should my plan of attack be? Check for power at the FV electrical connector? Bench test the O2 relay? I'm completely electrically illiterate so bear with me...

Responded to your PM.

I don't mind helping you off line for a bit as long as we close the loop back here in the forum as to what the issue is.

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^^^The relay. After you have a "buzz" (easily heard) reset that CO% back to 0.6 - 0.8! Make sure when you set the mixture that your front oil cooler is hot to the touch.

SOLVED!

Forgot to update this thread!

Turns out, it was the FV that was not operational. I removed and opened up the lambda controller/ECU and found a burnt solder joint.

Swapped in a working ECU (out of a 924 no less) and alas, the stove timer buzzing was back in the engine bay.

Big thanks to all the Pelicanites above, and for those who PM'd me. We've been on several many mile trips since. :)

I can tell you from experience, when a properly tuned to 0.9 CO '82SC has the lambda box take a dump from either the OXS relay or the box itself, the car will start wonderfully when cold but moments later run so poorly the tail of the car will shake violently side to side like a paint shaker! Been there, done that!