Z928328

Hello,

If you all remember I have a misfire. They found out its the foul plugs.

After changing the plugs & one side coil, caps & rotor (Other side just clean it) Car starts up fine & I can feel the power.

At random times especially when I want stop at traffic lights or wanted to park the car. The car idles rough- I need to rev up the accelerator then the car is stable again.

The shop said- It could be the fuel filter need changing. but some say it maybe the plugs wires.

Advice?

GuardsTurbo

If you don't know how old the wires are just swap them out at least from a preventative maintenance standpoint.

Z928328

wires are same age with the car.

nology wire good? my friend ask me to buy that brand.

GuardsTurbo

At this point any new wire will help with trying to diagnose your issue, but I don't know how that brand will hold up over time as I have never heard of it before.

Imo000

Don't waste your money on Nology. Just get a standard eplacement set from 928RuS.
If the engine isn't giving down at high RPMs the fuel filter isn't the problem.

To check the wires, get a spray bottle, fill it with water and then at night, in the dark, apart the wires and look for arcing. If you see any, replace the ignition wires.

dr bob

The fuel system on the car is constant-flow with a bypassing regulator, meaning a fuel filter issue will result in lower pressure/delivery but only really noticeable when there is high demand. Unless it's seriously plugged, a fuel filter won't prevent a car from starting or from idling. Under higher load, fuel delivery symptoms are more prominent.

"Leaky" plug wires similarly cause most symptoms at higher loads, when cylinder pressure is higher and the voltage needed to "fire" the plugs is higher. The "path of least resistance" is the rule for where the spark happens, so when a leaky wire offers a lower-resistance path to ground than the plug, you'll have a misfire.

Plug wires and connectors that offer higher and most importantly uneven internal resistance will manifest symptoms like uneven idling, but that's a hard "miss" rather than the more typical softer idle instability caused by uneven fuel flow through injectors. With a working oxy sensor, the FI controller manages idle mixture based on aggregate CO level from all the cylinders. With just a few partially obstructed, idle mixture isn't richened enough to get those few weak cylinders firing properly.


Conclusion:

-- If your wires are original, replace them for sure even if just as PM.

-- If the fuel filter is a worry, perform a fuel delivery test to make sure there's adequate flow available per specs. The test protocol is described in detail in the workshop manuals. If you decide to replace a fuel filter "just because" or because of low delivery, be sure to get the associated sacrificial pieces like the copper banjo seals, and have a replacement "S" pipe available (with it's own seals) for the likelyhood that yours will be twisted on removal.

-- Caps & rotors can easily be on a replacement schedule with the timing belt, practical since they are removed on the 32V cars as part of that project. "Cleaning Up" a used rotor typically involves removing the arc spatter on the tip, which increases the gap to the contacts in the cap when reinstalled... Causing bigger arcs and making more arc spatter. The cap includes a carbon "brush" in the center on a weak spring, designed to connect to the middle of the rotor. That brush is a wear point that drives the decision to replace the cap. These are really normal wear items that deserve to be on a PM schedule rather than waiting for symptoms. Collateral damage from worn caps & rotors includes the coils and the driver stages, as firing voltage goes up to the point where the coil arcs through insulation internally.

-- Oxygen sensors are wear items too, deserving replacement at 50k intervals. Similar schedule to the timing belt, although not specifically convenient to that job except that the car is on stands and you are already underneath for the flywheel lock. And the battery is disconnected. And the tools are out.



Lots of my WYAIT projects start out with a common element like "the car is raised" or "the belly pans are off". Often they are cleaning and detailing tasks, but grow quickly to include "I'll just check this one little thing that someone on the list reported a problem on" and such. My car is amazingly trouble-free, undoubtedly because of all the extra cleaning.

Imo000

I've personally seen the carbon points missing from distributor caps (BMW 850, very similar to the 32V 928 caps) and the engine ran flawlessly. Of the spark isn't ground to the engine, it will jump quiet a bit and still have wrong enough spark at the plug to make the engine run fine.

FredR

Besides the points already raised, other factors could be in play such as dirty injectors or a tired ISV [the device under the manifold that regulates the idle air flow].

Rgds

Fred

Z928328

ok..thanks..

BTW today I start the car-- I can felt the car didn't start right - SO I gave a bit of gas, the car stables. I let it idle for 15 mins & I drive it to the store.

As I enter the store junction- The car stalls without any warning. I restart it & the idle is rough- I rev the accelerator & the car is stable. So after that I blast the car at the highway for 10 mins. & car seems fine after that.

Fuel problem?

Speedtoys

No.


Straight old plain wires as a 928 kit are all you need.


If you had the tools, you could rebuild the set..but that's another thread.

dr bob

The "high performance" wires are typically larger diameter, so they don't readily fit the holders. The resistance that balances the firing voltage among the long and short conductors is in the plug connectors, so no magic is available from aftermarket plug wire sets.

Options for new wires include replacement wires-only sets that reuse the original connectors. Great if the original ends are in good shape. My be a good budget solution so long as you have the ability to verify that every plug connector is good and there is a a path from cap end to each plug.

The factory-fitted wires on my S4 have cylinder numbers on the cables, something mostreplacements can't. Our Favorite Suppliers offer a set of Beru wires as fitted from original, with all connectors new and looms/separators/supports identical to what the factory installed on the car way back when.

----

A thoughtful clinic patient gave me a set of replacement Beru wires that use the original end connectors. I still have them in their original packaging.Meanwhile, I grabbed a set of the original Beru wires a few years back, the closest to plug-and-play I've found. Decide what your time and aggravation are worth. I chose the "original Beru Plug-and-Play wires set" option, even though I have the wires-only set in a ox.

The Deputy

I'd stay the course recommended, new ignition wires.

Fuel issues normally don't disappear after 10 minutes of driving...but bad wires can show improvement once the moisture in the engine compartment has disappated.

Good luck,

Brian.