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Well, heck.... I went out on my lunch hour and it ran strong no bogging down or rough running (1st start of day).
Turned it off after letting it run/idle great for a few minutes. Went back 2 hours later started it and it ran for about 30 seconds and then started to run poorly.
I went to turn it off and noticed the IMS relay was green (normally don't have the cover off). I waited 3 hours and restarted it. Same issue. Green LED on IMS after 30 seconds.
I do not doubt I may still have a vacuum leak OR a leak of smoke through the bearings in the throttle body (I didn't replace them ) but shouldn't I fix the IMS issue first?
I think I will fashion a jumper and briefly see how it runs. I did check the coil cables/connections and all was good. I applied Deoxit just in case.
Well, heck....
I do not doubt I may still have a vacuum leak OR a leak of smoke through the bearings in the throttle body (I didn't replace them ) but shouldn't I fix the IMS issue first?
I can't decide which way Occam's Razor goes on this one. I have certainly see things break 'during' service that were clearly unrelated to the service (for example an LH dying during an intake/cc refresh) but usually Occam falls on the side of 'what did you last touch.'
In this case, I will opine that they are related. A 928 with intermittent idle misfires can run 'well-enough' that you might not think it's a big deal or maybe even notice, but if those misfires are on either side of the EGTs the IMS will trigger during warm-up.
What can cause intermittent misfire? Well, a bad A/F ratio. What can cause that at idle? False air directly to one or two cylinders. A minuscule amount of false air directly to a specific cylinder will result in a huge A/F imbalance because at idle the amount of required measure air is also minuscule.
So, I would chase the intake leak first, but concentrate on places where false air can get directly to a single cylinder. There are only - more-or-less - two: lower injector o-rings (which I think you would have found during your smoke test?) and the intake gasket itself. Taguid, above, notes that the water bridge can interfere with the intake. This is true for some 928s and not-as-true on others. But, that sounds like a general theory that fits the data so far. Except look to the rear of the intake cause that's where the cylinders are that are on top of the EGTs for the IMS.
Nothing jumps out to me at the moment for an obvious interference at the rear of the intake. But, the torque for the intake nuts is so low that even slight 'friction' of some sort that cause the intake not to seat uniformly on the gaskets will not be overcome when you tighten the nuts.
@Michael Benno - here's a YouTube video which shows smoke testing a 944. Super cheap but I'm questioning whether one wants to blow smoke through their MAF to test on a 928.
I'll post back my technique with pictures the next time I smoke test. I plan on getting a pipe to replace the MAF and using a hookup like below but with boot on pipe instead of MAF....
I think the same technique with a vape pen would work a lot better. They produce a lot more smoke and are pretty readily available.
I can't decide which way Occam's Razor goes on this one. I have certainly see things break 'during' service that were clearly unrelated to the service (for example an LH dying during an intake/cc refresh) but usually Occam falls on the side of 'what did you last touch.'
In this case, I will opine that they are related. A 928 with intermittent idle misfires can run 'well-enough' that you might not think it's a big deal or maybe even notice, but if those misfires are on either side of the EGTs the IMS will trigger during warm-up.
Makes perfect sense and I have no intention of ignoring the vacuum leak. I am just wondering if I've had this IMS issue for a while but not to this magnitude. I've just not ever been looking at the IMS relay when it ran rough/idled rough in the past. In fact, it has had a history of starting up rich and when I pulled the trigger on the intake refresh 12 months ago, it was struggling to idle after I came to a stop (cold or warm).
I replaced the MAF and LH with items from Louis Ott (picked them up about 7 years ago)
Originally Posted by worf928
What can cause intermittent misfire? Well, a bad A/F ratio. What can cause that at idle? False air directly to one or two cylinders. A minuscule amount of false air directly to a specific cylinder will result in a huge A/F imbalance because at idle the amount of required measure air is also minuscule.
This also makes a ton of sense. While it was running well, I did spray the the injectors and under the intake in a few spots with 3M AFM Cleaner. No reaction from injectors but a slight surge from the passenger side when I sprayed into the cavity underneath the intake where the throttle cable attaches to the throttle body under the intake. I am REALLY regretting not replacing those needle bearings!
Originally Posted by worf928
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So, I would chase the intake leak first, but concentrate on places where false air can get directly to a single cylinder. There are only - more-or-less - two: lower injector o-rings (which I think you would have found during your smoke test?) and the intake gasket itself. Taguid, above, notes that the water bridge can interfere with the intake. This is true for some 928s and not-as-true on others. But, that sounds like a general theory that fits the data so far. Except look to the rear of the intake cause that's where the cylinders are that are on top of the EGTs for the IMS.
Nothing jumps out to me at the moment for an obvious interference at the rear of the intake. But, the torque for the intake nuts is so low that even slight 'friction' of some sort that cause the intake not to seat uniformly on the gaskets will not be overcome when you tighten the nuts.
I assume there is no harm in cleaning the EGT sensors as suggested by DR in another thread (quoted below)
Originally Posted by DR
The most common issue is gonna be the EGT Sensors for the Ignition Monitor System. 99% of the time the sensor is just dirty and needs to be cleaned. In the old days we would swap them side to side to verify the issue. The most common side is the drivers side, but you can find out for yourself by pulling back the carpet from the Fuse Relay Panel and look to the far lower right of the panel Large Clear Device (see 1st pic below) with a Green or Red Light Glowing.. Red = Left side, Green = Right Side.
Green is the passenger side on LHD cars?
Think I need to replace the bearings when I pull the intake again?
If you wind up taking the intake off the car again check into the more expensive intake gaskets...they aren't paper and yes they run about $320 or ish but when you lay eyes on them you will see the difference.
I am in the middle of an intake refresh myself and have decided even though many have success with the paper gaskets to go with these. Just a thought if you are going all the way back in there.
Also not sure if possible but making sure you have a good flat surface on the intake manifold is important too...I know at least one person did a fantastic job on an intake refresh and struggled with a leak that if I am understanding correctly was traced to a fault in the flatness of the surface of one of the intake manifolds where they bold to the engine.
If you wind up taking the intake off the car again check into the more expensive intake gaskets...they aren't paper and ...
... neither are 87+ intake gaskets. They are super think rubber-encased metal-reinforced and will seal with ‘gravel’ inbetween them and the mating surfaces. The S4 intake is a totally differnt beast from the S3.
Makes perfect sense and I have no intention of ignoring the vacuum leak. I am just wondering if I've had this IMS issue for a while but not to this magnitude.
It is very possible that you've had some sort of issue for a while that was being 'covered' up by various factors that were corrected as a result of the intake refresh. It isn't uncommon for multiple failure modes to counter-act each other constructively such that fixing one reveals one or more others.
Nevertheless, follow your data.
Originally Posted by jej3
I am REALLY regretting not replacing those needle bearings!
Think I need to replace the bearings when I pull the intake again?
Smoke test 'indication' from the throttle spindle bearings is pretty obvious. Your major indication is - it would seem - not obvious.
It is likely you will localize your false air source and that you will be able to correct it without disassembling the plenum and air guide.
However, if you have the bearings and want to spend the couple of hours to R&R them then by all means go ahead. JUST REALIZE that the false air from your spindle bearings is not - it seems - the major smoke test indication you seek AND that false air from the spindle bearings effects the entire engine and cannot effect individual cylinders. Thus, IF false air is the cause or a major contributing factor to the IMS triggering, replacing the spindle bearings will not fix it.
I assume there is no harm in cleaning the EGT sensors as suggested by DR in another thread (quoted below)
Can't hurt. I would prioritize the intake leak though.
Green is the passenger side on LHD cars?
Just like the plug wires, it's not p-side/d-side.
Don't remember which color goes where. I always have to look it up.
Red is "Circuit I" Green is "Circuit II". One side will be 1,4,6,7 on pin 5 of the IMS relay, and the other is 2,3,5,8 on pin 2 (if I read the diagrams correctly.)
Somewhere on Rennlist someone figured out which cylinders goes to which circuit: green is circuit II on 2,3,5,8. The WSM and troubleshooting guide don't tell.
Run the engine from cold for 30 secs or so, then use a digital (fingers...) temp sensor to find a colder cylinder exhaust port. Do it quickly before heat starts to migrate. You'll find the culprit cylinder.
I had an intake leak on my S4 that I absolutely could not find without the smoke test. My normal strategy is to pull the intake and inspect everything, but it was a subtle crack on the inside of a bend on one of the hoses to do with the ISV and until I saw the smoke coming out of it it looked fine. I use a cheap ebay smoke tester and am pretty happy with it. I previously tried rigging up my own designs for smoke testers and had not much luck, but the ebay unit works well.
Well, I'm not sure a smoke test is the best way to go. Due to the IMS green light, I marked cylinders 2-3-5-8 (which is middle 2 on passenger and front/rear on driver side) with some blue tape just so I didn't get confused (far too easy these days )
I then decided to pull my pancake compressor out of storage and to my surprise it had pressure gauges on it and a pressure regulator!!! So I got the tank up to about 20-30 psi and dialed the outlet to the 3-5psi range.
Opened the valve to pressurize and voila (sorta)... I could hear a hiss from the driver side rear of the engine. I soaked everything Vacuum or needing to be air tight in Windex (because I am chasing vacuum issues on my son's 1987 924S right now, too ) I was so focused on the intake I didn't give any thought to the cam cover. Light bulb goes on and I can physically feel air escaping at the bottom of the cam cover.
So, I am going to pull the driver's side cam cover and reseal it (hopefully) I still have a lingering issue with some small amounts of smoke under the intake, which could still be a problem but I hope fixing the cam cover leak is move towards fixing the IMS "green light" issue.
Thanks for the encouragement, @worf928 and @dr bob . I hope fixing the Cam cover sounds like the most prudent move at this stage.
... I am going to pull the driver's side cam cover and reseal it (hopefully)
Use some safety wire twisted like a bread sack twist-tie at each corner through the bolt holes to keep the corners of the gasket in the groove when you place the cover. Then when you have the other 9 bolts started, snip the wires, pull them out and turn in the other four bolts.
Seems like I am on the right path. Only traceable air leak was from flappy bearing and during air test, which was the same as before, the rubber cap popped off the MAF!
Idle was more solid than I've seen in a very long time.
Thanks to all but especially Dave ( @worf928 ) and @dr bob for the sound advice and encouragement.
Need to do a few remedial things before I can road test but I can definitely say I've missed hearing my 928 run well.
01-28-2019, 07:30 PM
) but shouldn't I fix the IMS issue first?
