jwbeck17

So I have been running the car in the driveway for about 5+ min (engine warned up) with the throttle to keep it going, and if is running really rough with low idle. At climbing rpms you hear a lot of bass “burble” from the exhaust. No green lights seen in the brain where the IMS relay lives.

So I got the costs from Roger to do a MAF Rebuild and tuneup (even though some of the parts may be newish, probably should do I it once together).

Before I throw money at it, I’ll do the LH/EZK testing with my multimeter...however I am fairly unskilled a this. Your directions are pretty clear, but I just want to be sure before a break or short something...

- When testing the LH/EZK pins should car be off, running, or just with the key in the on position? i'm guessing off.

- am I testing the pins on unit bolted to the body, or the pin receivers on the harness and covers? I'm guessing pin receivers on the harness is what is being called the connector and not the modules connected to the body.

- is the inside unit in the silver box the EZK and the black box closest to the wall the LH?

i was able of get the harnesses off of then and connections are all clean, dry and not corroded as the units were rebuilt a few years ago.

worf928

Based upon my mental picture of this description you have one or more cylinders that are not firing. Bad plug wires, or a bad coil wire. Or one or more injectors not firing. Poor connection to coil.

There's both a red and green LED in the IMS relay. The color tells you which 4 cylinders have had fuel cut. If we assume that the IMS relay is functioning and not lighting one of the LEDs this tells us that prospective misfires on are cylinders #1-3, or #5-7.

Diagnose twice. Buy parts once.

Note that the tests in my guide have nothing to do with testing the ECUs. Their purpose is to test the function of components on the engine that 'talk' to the ECUs.

In your video it didn't seem like the engine was running as roughly as you describe above. However, let's go with your description. In that case, I think determining if you have good spark and good injector pulses is first. If the engine is running as roughly as you describe then it's not the idle switch or stabilizer.

Car off. Key off.

Figure 43 shows clearly what you will test.

Refer to Figure 37.

Check the female pins in the harness-side connectors too.

jwbeck17

All clear now...for now. This really is a great write-up on the diagnostics and I look forward to testing it out tomorrow, weather willing, and will share results.

jwbeck17

Got some results from testing and we may have found a problem area...

Temp II Sensor: GOOD
- At 81 deg F: 1.66 KOhms EZK/ 1.66 KOhms LH
- After 5-10 min warmup(Est 150-200 degrees F): 258 Ohms EZK/ 271 Ohms LH

Idle Switch: GOOD
- No Throttle: 1 Ohm
- W/Throttle: Inf

WOT Switch: GOOD
- No Throttle: Inf
- W/Throttle: 1 Ohm

ISV: GOOD
- Made clicking noise when jumpered for power and grounded

Flap: GOOD
-- Made clicking noise when jumpered for power and grounded

Tank Vent: ISSUE?
- no noise when jumpered for power and grounded
- Son listened and said he saw slight smoke rising from tank vent area/harness
- Ground cable got very hot in test

The only other diagnostic I could think of doing is running the engine with the MAF unplugged to check performance.

For an example of how the RPMs and engine sound are working currently under steady throttle at warmup, you can see in the attached video that the engine is "hunting" with RPMs going up and down. Once I let off the throttle at the end, the idle drops and stalls.

Any thoughts, suggestions or ideas now?

jwbeck17

Since my son son a little smoke puff coming from where that bandaged LH harness is, I decided to unravel my protective cover and see what is under it. Not pleasing, as I can see wire that is unprotected in spots and exposed copper wire in others. See pics and let me know your thoughts.


I removed the vulcanized tape and head shielding that I had put on the LH harness a while back. you can see places where the plastic shielding has cracked and exposed wire (though still insulated)

Looking at the connector by the cam cover, here you can see some exposed copper and signs of melting.

jwbeck17

Update #2:

I was able to remove the MAF connector to test engine function without the MAF, and it started up and idled smoothly. Any acceleration was a problem as expected, but it did idle nicely.

Reconnecting the MAF, a ran into the same issues with idle again.

I did add some deoxit to the MAF pin receivers on the cable though the middle 4 looked clean.

What I did notice is MAF connector boot wear, exposing the wires inside.



Interested in your viewpoints here. I am thinking the following:

• Either MAF or MAF cable is the failing element here causing the rough running.
  • I do not have another MAF to test, so I may have to order one from Roger and send it back if that is still the case
  • Not sure how best to address the MAF connector issue - If MAF replacement works (meaning the MAF wiring is fine) i guess I wrap it?
• While The LH Harness is not in good shape, I suspect that is not the failure point, though should be resolved somehow. Not sure if I can replace the LH harness like i did the engine harness

linderpat

I'm thinking your issue is with that harness.

jwbeck17

I looked at the wire diagram and it looks like the MAF connector, tank vent, flappy, etc. are all part of that LH harness. I wish I could just buy a fresh LH harness from Roger and install in 30 min in my driveway then have a cold one, but I guess that may be wishful thinking, huh...

I'm thinking my next step is to do some further inspection and possible repair of the LH harness (using self affixing heat resistant tape and possible soldering of bad wires points, along with Deoxit cleaning of connectors) to see if that will change the current performance. However if any of y'all have heard of a LH replacement solution, I'm all ears. After that I should know if the MAF is toast or not.

Any other suggestions from the wise?

jwbeck17

So after some Internet searching I think I answered my own question. There is a replacement for the LH harness which would be the injector harness. It sounds like that is something I could get from Roger and Sean...though I expect at a hefty price due to it complexity as it covers LH and EZK connections and it much more involved than the engine harness. On a positive note, I read a post that Stan replaced it within 5 hrs in a parking lot, so that's promising.

So I am back to my inspect and repair plan, then will go from there.

FredR

I would suggest the first thing you need to do with that MAF connector boot is remove it and inspect the cores back towards the harness a coupe of inches or so. If they look suspect it is not too hard to revive the cables one at a time.You need a safety pin to help you remove the cores from the 6 pin plug.

I did this a few years ago and cut out the suspect looking cores and spliced new cores back in the main harness run where the cables looked to be in excellent condition underneath the heat shrink that was baked hard. Some frown on the idea but I used crimped connectors but either way it is not too difficult to solder new cores in and cover with heat shrink sleeves. You could even install a new 6 pin junior power timer connector or whatever it is they are called. Needless to say I did not have the correct colour cables but as long as you get them in the correct slot it is not the end of the world but you should be able to get some correctly coloured cables with little problem.

worf928

Note that since IB has removed my ability to edit my own posts:
- there may be errors below that I cannot, after posting, correct except in a follow-on post
- this will be my last 'help' post on this forum until I've the ability to edit

It is certainly part of the problem.

Yes. This is an issue.

First, I re-reviewed my guidance in my doc on these tests. I didn't make it 100% doubly, super-crystal clear that closing the circuits during these tests should be *momentary.* A 'touch'. A 'click'.

** Do not keep the circuits closed for more than a fraction of a second! **

Nevertheless, your observation on the tank vent is two issues:
- your tank is not being vented unless you have a cracked/broken hose in some part of the venting system. This can cause you tank to collapse!
- the fact that you saw smoke means that the circuit for the tank vent is shorted.
- this can cause your LH ECU to release smoke (not a good thing.)

You should disconnect the tank vent solenoid and test the solenoid directly. And you need to fix the short in the harness branch!

And that is the connector to the tank vent solenoid.

This is another sign.

Or, connecting the Mass-Air Sensor is what enables short-circuits in the LH harness.

That is the incorrect procedure and if Roger knows he will not send you a working unit to test in your known-broken car.

Always put a suspect component in an otherwise working 928. If you put a known-good component in a non-running 928 there is a risk of the problems with the subject car breaking the otherwise good component.

This is *exactly* the reason why electrical components have no warranty if plugged-in!

Roger may, however, agree to test your Mass-Air Sensor in one of his 928s.

Alternatively, there are no doubt other, working 928s, in your area the owners of which may be willing to test you Mass-Air Sensor in their 928.

But, don't swap their components into yours.

Diagnose first. Repair when data is sound.

No. It is a failure point as evidenced by the tank vent test. You do NOT want a known short circuit in any harness.


I am not aware of the current stock of LH harnesses at Porsche. Few if any are left, I susepect.

However, I believe Kroon makes replacements. Not cheap.

Expect a new replacement to be at least $2000.

You need to 'ohm it out' with a multi-meter in order to see if you have other problem areas other than the tank vent.

At a minimum you need to repair the tank vent branch with a new connector (so as to remove the few MMs of bad conductor.)

However, from the looks of your harness, I'm going to bet that nearly every bit of it is as hard as glass and just as brittle.

If I was 'there' I could in a few minutes make a decision on if your harness is worth attempting to save.

Since you are in PA you can't be far from either Stan (MrMerlin) or Earl. You might consider reaching out to them for advice or help.

As far as I know only Kroon is making new replacement LH harnesses.

However, Mark Anderson might have a good used LH harness for your model year.

Get your Mass-Air Sensor tested in another car *first*.

Repair the tank vent branch of the LH if you can and if the other-car test of your Mass-Air Sensor indicates that it is bad.

jwbeck17

Great points, Dave, and I really appreciate the clarifications and explanations.

To respond to your statement about the brittleness of the wire, I know at the very minimum that the once the wire casing comes out from under the fuel rail (the protection sheath underneath the rail feels flexible and normal though I haven't seen the wire situation yet) and flows to the front of the engine, it gets really brittle. Looking at the tank vent wire, there is not only exposed copper at the base of the boot, but also the wire insulation is cracked due to flex, so not good. One thing I am planning on doing today is a thorough inspection of the harness to identify any other weak points and repair them as best as I can. I will also test the tank vent solenoid directly with my probe. My goal will be to see if the repairs fixes the situation for now, knowing that a partial or full on replacement may be in my future.

Second step will be to make another visit to Stan, as he has seen this car a few times and just did the timing belt this spring. (I also had the pleasure of working on a pesky alternator issue with Earl some years back where we spent equal time working on the car and sitting in lawn chairs reflecting on Porsches and the car experiences of our past. It was lovely.) Stan has been very good at identifying the areas that I can fix vs needing his skills and he has been a great guide and friend.

Once I finish doing my checks and repairs today I'll get back with an update. Thank you all for the help!

jwbeck17

Just finished today's work on the car and got good and bad news...

• I inspected the injector harness from the firewall to the timing belt sensor and based on what I saw and felt, only the tank vent sensor wire path is fried.
• When I opened up the MAF boot, the wires seemed somewhat flexible and intact. Just the boot had a hole in it from heat and drying out. I cleaned the wire area to ensure no breaks, wrapped the exposed MAF connector base in rubber self adhering tape, "deoxited" the contacts, and put the area back together.

The bad news is that, as expected, the tank vent wires are in bad shape. I removed the head shielding plastic up to the injectors for inspection. The other related wires, such as the Temp II sensor and Timing Belt sensor had all been spliced in and replaced, so they seem flexible. Once exposed, the tank vent wire had numerous breaks in this insulation as well as the plug itself. I did what I could to patch the wire by covering the exposed wire areas in electrical tape, then recovering the exposed harness area with new split wire heat shielding.

As for testing the Tank Vent solenoid directly, I need to figure out how best to do that as I am a little new to that kind of testing.

I tried to run her again, and same issue. Probably the next best steps are:

• Test the Tank Vent solenoid (once I know how to do it)
• Order a new tank vent connector pigtail (and possibly solenoid) from Roger
• Test my MAF on another S4, if possible, to determine if I need a new one

Here are some pics of what I found:


The harness coming in from the firewall looks in good shape


The harness split behind the motor had a little gunk on it, but no signs of damage

the harness cover was flexible through the fuel rail but got stiff at the first harness split where you see the Temp II sensor wire


When I exposed the wires from the brittle heat shielding, it was only the tank vent wires that showed wear.

I don't think this tank vent wire is factory spec...

I cleaned the wiring up the best i could.

jwbeck17

This morning I put my power probe to the tank vend solenoid and I "think" it is functional, though it is hard to tell. If you have tested it, let me know if this is the faint sound i am looking for.

I hooked my probe up to the jump post (power) and crossbar nut (ground) then the negative probe connector to the ground tab on the solenoid (the one closest to the engine). using the power probe, I first touched the positive tab on the solenoid and the green negative sign lit up on the probe, indicating continuity through the component. Next, I triggered a few quick bursts of power, which changed the indicator to red negative. Per the power probe instructions this indicates a correctly functioning component. In addition, you will hear an additional click on top of the button click that I believe may be the solenoid sound referenced by Dave in his tank vent test. To try to confirm I disconnected the probe from the positive terminal and clicked power, and I only heard the button click.

Is it fair to assume that I have a correctly functioning tank vent solenoid? I am assuming that i will replace the tank vent connector at any rate due to it's quality.

If you agree, then my next steps are:

• Order a replacement tank vent connector from Roger and solder in
• See if it is possible to do a MAF swap test. Maybe Stan will help? Or is there another S4 in the Philadephia western suburbs?
  • If MAF is issue, will order a replacement/core swap from Roger
  • If MAF is not issue, I may need higher level of diagnosis through Stan and possible injector harness replacement
• I also plan on doing a tune-up, replacing the spark plug wires and other standard tune-up bits as I am not sure when the last full one was done and the car is at 150,000 mi.

Here is the video of the test:

jwbeck17

Now I am throwing money at the problem, but hopefully money well spent.

I'm sending the MAF off for testing. I suspect it may be the primary issue and needs a rebuild, but I'll let Louie Ott tell me.

The tank vent solenoid worked per my test, so I am checking with Roger to see if I can get a tank vent connector pigtail from him that I can connect, which should be done anyway

Also I am doing a tune up since I haven't seen one done fully in its recent history. I got spark plugs about 7000 miles ago, but they are not expensive to replace, and replacing them along with the distributor caps, rotors, coils and spark plug wires (which are cracking) is just regular maintenance that should be done.

While I am doing that, I'll replace the Hall Sensor too as Stan had alerted me this spring to that being functional, but extremely brittle and not long for this earth.

With those items completed along with the other work completed prior, I hopefully should have a very healthy 928 engine for the foreseeable future.