Ron: exactly. I just took the old plugs out and most of them had a gap of 0.035. Some HT wires are questionable too so I will replace them as well and replace the plugs with a 0.025 gap setup.
Paul: I did the shake, rattle and roll - no impact.
Thanks
Stephan
Hi Stephan,
Looks like I now need a scope to trace out what’s happening with my ignition. What is the manufacturer and P/N for the scope you are using. Anybody have any scope recommendations?
More thoughts on your stumble. I feel that your problem is in the ignition
area given that the stumble is intermittant and characterized as a stumble. If it were a fuel problem, intermittant fuel would not produce a stumble. Gas coming on or gas running out would produce a linear reaction like running out of gas or going richer would produce a linear increase
or decrease in rpm. Much like when running out of fuel altogether or increasing the gas. One doesn’t get an abrupt change but a slower, linear change in the engine rpm. If you can look at the center leads to the distributor to see if there are any intermittant sparks
occuring. This is also a good time to shake, rattle and roll all ignition leads at the plugs and also at the pickups and any wiring into and out of the ignition ECU. If you can use your scope to see the sparks at the plugs and distributor, this would also yield good
info.
Paul
Hi Paul,
I agree with you: I already replaced all plugs and ensured correct gaps (old plugs were around 0.035) and am now waiting for a new wire set. Believe it or not: After I re-installed all ignition wires, mounted the A/C compressor back into location and installed the throttle tower and the cruise control bellow, I found one ignition wire arcing. Which one? 1A!! Murphy’s Law, I guess. The wires I use are about 10 years old so I decided to get a new set.
Re your scope question: I have an old-school 'scope, but recently got a cheap ($40) digital scope with a 2" screen to provide me with some directional, preliminary results. That is one you see on the photos. You can get them on eBay or via www.jyetech.com. I can not use this scope for the spark tests - for that I would need an inductive pick-up (a coil). Perhaps I should look into that…
Thanks
Stephan
Hi Stephan,
The spark voltage is so high you might be able to just use a wire wrapped around the plug wires, one maybe two times.
Paul
Hello Paul,
yes, that is what I am planning to do (once I have some time available). Several windings should do the trick, ideally I will find an easy “clamping” solution.
Stephan
Stephan. You might can find an old used timing light for cheap that has inductive pick-up clamp. Re-purpose the clamp and throw the strobe away if not needed
Jim
great idea - Thanks!
Paul: After I replaced the ignition wire set the idle improved - not yet perfect, so I am going to re-adjust the butterflies next.
Stephan
I use mine as built. The strobe detects spark.
No really old tech cars in my present stable. Miss them, or do I???
It has been a while - Here is an update where I stand with my stumble situation: Installed a new set of ignition wire, however, no improvement. Then I looked at the distributor base position and learned from the forum, that at TDC the rotor has to point at a certain indicator on the distributor base. I was hoping to find a TDC marking on the crank pulley, to no avail. Does somebody know if the Marelli equipped cars have a TDC marking?
While I am aware of the option to manually crank the engine to identify TDC at #1, I was looking at the distributor cap for some indications of spark between rotor and the copper posts of the cap: At several posts I found traces of spark residue next to the respective posts, i.e. in direction of rotor rotation. That made me believe that spark energy was going to the post after the rotor already passed the post. So - in several steps - I re-adjusted the distributor base by turning it in rotor direction. After each adjustment I drove the car for a while, then checked for new spark residue and copper post surface condition. The rotor now is facing the respective cylinder post when spark happens. The idle stumble significantly improved, however, I am not on that permanent “turbine” level that I would expect from a V12. I have to say, though, that on occasion, it is running very smooth.
Question: Having eliminated vacuum leaks, butterfly adjustment, poor electric contacts and wiring and bad sensors as root cause, can the ECU itself cause problems? Components inside the ECU are 30 years old and bad capacitors could cause some irregular behaviors. Does anybody have a circuit diagram of the ECU (1990 Marelli)?
Thanks
Stephan
http://www.jag-lovers.org/snaps/snap_view.php3?id=1402280159
Picture 5 shows the marking (must look carefully from under the car)
Picture 6 shows the proper orientation of the rotor while the engine is at 1A TDC.
What you are doing is precision guesswork – the dizzy should not be rotated this way.
On the other question – there is one place that can service a bad 16CU that I know of – AJ6 Engineering in the UK.
Every other link that you can find on this forum is for the 4L 6-bangers, the latest AJ16 variants, and the repair results are not always satisfactory
Steve
thank you very much! Unfortunately, I can not open the photos (except #6). Do you have them available in a different format perhaps? I would be obviously most interested in #5 (TDC marking). I was also trying to open the photos directly from the Album section without success.
And yes you are correct: I am doing “precision guesswork” right now. I have heard about AJ6 Engineering but given that I my background is electronics I was attempting to at least look for the obvious (e.g. bad components) before I would venture to send my ECU over the pond (and not even being convinced that this is the culprit).
I did some further investigation today and found that the stumble is coming from the “A”-bank as the right exhaust is slightly vibrating and the exhaust sounds remotely as if the engine would randomly misfire.
I visually inspected the injectors in their seat and found that I can easily rotate some of them a few degrees back and forth. Now if the rubber seals around one or several of the injectors were not properly sealing and thus allowing air being sucked into the intake: Could that cause the symptoms I am describing here? I am looking into the fueling as I have exhausted the ignition end of it.
Thanks again
Stephan
Nobody can, unfortunately. Most of photo archives are lost when the old site as decommissioned.
I found this picture which should give you an idea where to look:
That does it. Thanks! Any idea on my injector seal question?
Steve,
one more question. In your photo #6, it looks like the nudge in the distributor base (where the arrow of the rotor is pointing to) is facing the windshield (towards the rear of the engine). Correct? In my car, this nudge is facing the front of the engine…
Stephan
No, the notch is ion the front. All Marelli’s – 5.3L or 6.0L are the same.
Regarding the injectors’ seals – I don’t think this is your problem, if you have a problem at all.
I’ve chased this rock-steady idle for years and have done everything you did, plus a lot more.
+/- 50 at idle is the nee norm :-))
But, if your 30 years old injectors have never been serviced, I’d recommend doing them. It won’t hurt anything
Thanks Steve. I have a stable idle rev, but some stumble originating from the “A” bank. You are probably correct that the injector seals are not my problem, but I want to rule out all options…
BTW: I also replaced the distributor cap (Marelli and aftermarket) to no avail. My injectors were serviced around 10 years ago (and less than 10,000 miles since) by SD Faircloth.
Stephan
