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In one of the previous posts, I saw reference to the test procedure described in the WSM. I found it and thought I would post it for thread viewer convenience:
Digital File: Manual Volume_1A.pdf Page: D24 - 25
Test point 18: Intake system leaks
Check all connections after the air mass sensor for tightness and freedom from leaks. Attach special tool 9264/1 to the air mass sensor with M 4 x 45 mm bolts and build up a pressure of 0.3 bar (4.4psi). If there are any leaks, pressure will drop in the intake system or air will be heard escaping. Note: On cars with oxygen regulator, flashing fault code l-23 (oxygen regulator at rich stop) appears if there are severe leaks in the intake system (for example the intake pipe gasket).
Porsche special tool 9264/1
Dwayne Special Tool Equivalent
I have done the following to try and rule out the IMS Relay Green LED light.
1. Cleaned EGT Sensors and re-installed
2. Used an IMS Bypass Relay to run without IMS issue for detection of engine miss. Pulled plug cables, while running for 2-3-5-8, no noticeable difference when any were pulled. Pulled wire 4 and notably the engine changed.
3. Decided to clean the driver side distributor cap as it appeared dirty and contacts cleaned up with Deoxit and some 800-1000 grit sandpaper.
4. Swapped back to IMS Relay.... Green LED after 18-30 seconds.
I am going to order an inductive timing light off Amazon so I can guarantee spark. What else should I be trying? I know much of this thread focused on vacuum leaks from intake refresh. I have NOT taken off the intake yet as I don't seem to have enough time to do that again (but I will make time)
My question is, what else would you check? What causes an entire bank of cylinders to seem like they have no spark?
I am starting to think aging (or the A.D.D. I get working on a 928) is destroying my ability to focus on this and problem solve. I appreciate any help you can give. If you feel I need to pull the intake and start over, I'd respect anyone telling me to do that.
Ancillary Info -
Coil Wire on both sides have been swapped with NOS purchased previously
Spark plugs look uniform across all cylinders
Cap and Rotor replaced 7 years ago with wires
MAF and LH replaced 7 yeas ago. Swapped MAF in from another S4, no effect either way.
Swapped Ignition Amplifiers - No effect either way
Still hoping to bring two cars to Rendezvous but really need some guidance.
Verify that the firing order is correct, plug wires plugged into correct ports on the cap, correct wires to correct plugs, etc. This should get you past the IMS protection issue.
Your local parts store should have a free-rent timing light if it's needed to verify spark energy to each cylinder.
I ended up taking some extra care keeping the plug-well donuts in place while setting the cam covers in place. Ended up using a mini-mirror down each plug well for a 360º sideways look around at the bottom of each hole.
Peeking back on posts 24 & 25, what was the result of the testing? If the IMS is dropping 2-3-5-8, remember that the temp probe is under either 2 or 3, depending on year. Focus your attention on the plug wires and the injectors for those two cylinders. You can hear an injector clicking, and you are looking for the ones that aren't. IMS will drop the injectors on 2-3-5-8 after about 30 seconds of running, so you'll need to be pretty quick to listen after you start the engine. Either the plug wires are crossed or (at least) one of those injectors (2-3) isn't firing.
It's going to be one or maybe two simple easy stupid things. It always is.
Thanks, @dr bob . The IMS Temp probe is under cylinders 4 and 8. I've confirmed that all 8 of the injectors (especially 2-3-5-8) are firing with a mechanics stethoscope on each when the IMS Bypass Relay was installed and the IMS Relay was installed (just had to move quick, like you said). I originally had an issue with either the #2 or #3 injector but it became "unstuck" and seems to be clicking with the same intensity as the others.
I'll definitely re-check all the plug wires first when I get home in a few days.
Assuming the plug wires check out... What can I swap over from my 88 to the 90 to test? I've already swapped MAFs and Ignition Amplifiers. Are the LHs compatible between the two? Does the LH control the ignition "banks" or asked differently, if I find I have NO spark, what would take out the ignition bank? (Ignition Coil, Cap, Rotor)? Can I swap these things out?
All the modules are interchangeable, as are ignition and injection system components. The IMS system didn't exist on the earlier car.
If the probe is under #8, focus on that one as only one cylinder in each ignition bank is tested. Then all the injectors for that bank are disabled if the one tested cylinder is colder. If plug wires are accidentally mixed, the temp-sampled cylinder plus one other will be cold. That finger-tips temp test I described earlier is a pretty simple way to find those that are not firing and have cold exhaust ports..
Feeling truly crazy. Hooked up inductive timing light. TIming light fired for cylinders 2-3-5-8. Checked Cylinder 4 and light fired. Mechanics Stethoscope confirmed all injectors were firing at idle. Sounded like a slight hesitation or miss when I hand actuated the throttle. Not sure what would trigger IMS but I tested all of this with the Bypass relay in.
I suppose I can move IMS EGT sensors between sides. Is that the next step to figure out if I have a faulty sensor?
Okay. I've 100% confirmed I have spark (using timing light) on all 8 cylinders and i have fuel injection on all 8 cylinders (with Bypass relay installed).
I will be following the procedure to test the sensors. I still have sneaking suspicions about the Fuel Injectors maybe not being 100% (because I had one that was originally stuck) and I also have suspicions I might have some form of a vacuum leak from the intake refresh but it doesn't seem to be obvious and definitely isn't with one of the injectors.
This is really frustrating. I'll jack it up one more time and run it to see if the exhaust ports for 4 and 8 are different temperatures with an IR gun. I do get some condensation out the tailpipe when I first start it... I assume this is normal. It certainly doesn't smell or taste like fuel.
I replaced the fuel injectors and immediately started last year right before SITM. They were from a company online not five0motorsport but tiger something. One injector was "stuck" and when I first restarted so I was running on 7 cylinders. I have a replacement injector that I received a year ago for the stuck one but I "unstuck" it by applying voltage and light tap. Since it took 2 weeks for the spare to get to me, I never swapped it.
Just put a gauge on the fuel rail and it was up to about 48 lbs and under load was 42 or 43lbs. Going to look and see if that is normal. I have new dampers and FPR. I'm going to play injector swap with the spare one on cylinders 2 and 3, because I don't remember which one was stuck, but honestly am leaning towards getting a brand new set of 8 Gen II injectors here...
I think I am okay with fuel supply when running as I'm 48 psi (3.3 bar) at idle BUT after a quick lunch (25 minutes) the pressure was way down in the single digits. I think I may have a leaky and thus probably a bad injector. Is that plausible?
Test 1 - Swapped out the #2 injector for the spare and there wasn't much change (stumble still present)
Test 2 - Swapped out the #3 injector for the spare and there was only a small hint of stumble and/or vibration (running in hot garage without air filter on).
I need to see if I get the IMS led but I'm expecting I will (note there is no noticable gas in the exhaust AND the cats do not change color or GLOW)
I'm still quickly failing the leak test above with my minimum pressure after 20 minutes being in the single digits (PSI) Is that an issue with a fuel damper? My idle pressure is 48PSI (3.3bar) and my pressure under load is around 42PSI (2.9-3.0 bar).
I don't think I have an ignition problem as I swapped over coils and changed out spark plug cables individually for a spare set.
All injectors (1-2-3-4) ohm'd out at the same resistance 16.0-16.2.
Wondering if I should just go for the new injectors?
Looking for more thoughts on my fueling situation and YES, tomorrow I'll be testing the IMS sensors per the TSB that Rob posted.
The "quick test" for a faulty injector is to pull the leads off one at time. If the injector is good you will feel the difference in the way the engine runs if it is bad it makes no difference - La voila! If you are losing fuel pressure that quickly in static conditions then either the check valve at the pump is faulty or you have a leak between the pump discharge and the pressure regulator that could be caused by a leaky injector or injectors. If a leak exists then obviously it needs fixing irrespective of whether it is the root cause of your running problem.
The "quick test" for a faulty injector is to pull the leads off one at time. If the injector is good you will feel the difference in the way the engine runs if it is bad it makes no difference - La voila!
True. However it isn't easy if you don't have a GTS with the spring-loaded 2-pin connectors. If you have the Bosch 2-pin disconnect tool then it's easy on pre-GTS.
If you are losing fuel pressure that quickly in static conditions then either the check valve at the pump is faulty or you have a leak between the pump discharge and the pressure regulator that could be caused by a leaky injector or injectors. If a leak exists then obviously it needs fixing irrespective of whether it is the root cause of your running problem.
Static pressure leak down has three causes: bad check valve at the fuel pump. Bad check valve in the regulator. Leaky injector(s).
02-03-2019, 02:08 PM
