86 Carrera Fuel Damper

[nene]

What would be some symptoms of a faulty fuel damper on an 86 Carrera?



Serg

[BGCarrera32]

Depending on if you are specifically referring to the pressure damper on the passenger side injector rail, or the pressure regulator on the driver's side rail (or both), beyond poor running you can have:

1) hard restarts as the pressure in the system isn't holding but leaking down because the regulator is shot and can't hold pressure

2) different AFR readings on the right bank vs. the left bank

Step 1 is to attach a pressure gauge to the fitting on the driver's side rail to check operating pressure and leakdown pressure over time after the engine is shut off.

[DRACO A5OG]

^^^+1 check the pressure

[scarceller]

Biggest failure is a ruptured/leaking diaphragm, if that happens then fuel seeps out the vacuum port and gets sucked directly into the back of the throttle body. Depending on how bad the leak is you will go rich, especially at high vacuum like idle and light loads.

Pull the vacuum line and see if you have fuel at the port or in the line. Also do the same test on the Fuel Pressure Regulator on the other rail, either can fail in this manner.

Other than that the dampener rarely fails. It's basically a reserve tank that helps keep pressure constant when all 6 injectors fire.

[nene]

BGCarrera32,

Thanx for you response. I am referring to the one on the passenger side. No hard start issues, but trying to isolate if one of the regulators is playing a role in my ongoing quest to find out why my revs/engine needle drops down suddenly when driving. It is more apparent when cold than hot.

I don't believe it is a vacuum leak, as I am unable to find one.

[nene]

Great info guys,

Now, I have pulled the vacuum lines from both and no gas leaks. If I pull the vacuum hose from the dampener, I see no changes in the engine idling.........should there be?

[scarceller]

Originally Posted by nene

Great info guys,

Now, I have pulled the vacuum lines from both and no gas leaks. If I pull the vacuum hose from the dampener, I see no changes in the engine idling.........should there be?

No, that vacuum line does nothing, it's there just in case the diaphragm gets compromised you don't have fuel all over the motor! The line is a fail safe to catch fuel and suck it into the intake.

But if you remove the vacuum on the FPR on the LHS (drivers side) you should notice a slight change in idle quality since the mixture gets richer.

When you say the tach needle drops does the engine cut out also?

I doubt a sudden drop in tach reading is related to the fuel pressure. I suspect ignition related is more likely.

[nene]

Upon depressing the clutch to shift, the tach drops (hard), but does not die, it idles fine. Now, when the engine is warmer the tach needle drops easier and thus making shifting easier. This has been bugging me and would like to nip it in the bud.

I have also played with the AFR adjustment including "the wheel" to no avail. I use an LM1 BTW.

[nene]

Interesting, I am familiar with the timing, but thought that for this model no manual intervention was needed??

[scarceller]

You are experiencing idle dipping. Is the motor stock?

Few possibilities:
- Have you set/verified that base idle speed has been correctly set? You need to follow a specific procedure to properly set base idle, do you have that procedure?

- Have you also verified base mixture? You need a decent WideBand O2 gauge/tool to properly set mixture. Would be nice to know exactly what the Air Fuel Ratio is at idle.

Have those 2 things been verified?

Also, you can not alter ignition timing without a chip change. Are you running the stock chip? I ask because some chip companies screw with idle dip and attempt to fix it, would be good to know what chip you have?

[nene]

Yes, base idle has been properly adjusted, verified mixture and AFR is approx 14.2.
I have a wideband guage that I use to calibrate the AFR, which I purchased for this reason, and I am running a pretty much stock engine/chip. I also checked the FQS which is set at 0 (default).

[scarceller]

What RPM did you set base idle at? 800RPM or 880RPM? 84-85 cars idle at 800 while 86-89 idle at 880, I mention this because the bently and factory manual have the base idle spec at 800 but that's not the target for the later cars.

I also suggest setting the base a tad higher than the target, it helps with idle dip. Try setting base idle at about 920-950RPM and see if that helps.

Your AFR of 14.2 at idle is good, I use 14.2 to 14.4 range for idle mixture target. But be careful not to let it idle to long when you set this. You want to see it at 14.2-14.4 when you return to idle while driving, like when you come to a stop light.

Also, do you know what the AFR is at under cruise conditions? Like cruising down the hiway at 3000RPMs in 4th gear on flat stretch of road? You should be in the 14.4 to 14.7AFR range with the O2 sensor disconnected.

[nene]

Scarceller,

I do not know the reading at cruising speeds.

Now, I have the 02 disconnected because the car drives like crap with it, even when the car is warm.

[scarceller]

Originally Posted by nene

Scarceller,

I do not know the reading at cruising speeds.

Now, I have the 02 disconnected because the car drives like crap with it, even when the car is warm.

If you do not have a cat converter then simply do NOT use the O2 sensor.

The reason it may run bad with it connected is that the sensor may simply be bad. Often when they fail they either short out or put out false voltage, if they short they send false lean data to the DME and the DME then richens the hell out of the mixture in an attempt to fix the false lean condition. The inverse is true for a false rich condition.

Without the O2 connected the DME simply runs like Rest-Of-World (Euro) setup and these motors actually idle better slightly rich.

If you have the ability and time do get some AFR data at cruise loads.