Well I've looked/listen to numerous videos and I can't find anything that replicates the noise that my 1999 XK8 is producing.

Video Link

The knock has a consistent wave pattern (comes-and-goes, versus knocking every rotation). Idk if it's correlated, but this knock (and rough idle) came after replacing the MAF.

My troubleshooting process:
Lean codes (P0171 & P0174), but smooth idle and no knock --> Seal all vacuum and exhaust leaks, new MAF, reset ECU --> Drive Cycle --> Rich codes (P0172 & P0175) --> MAF error (P0101), Rich codes (P0172 & P0175), rough idle, engine pattern knock --> reinstall old MAF, reset ECU --> rough idle and knock are still present --> clean and test MAF plug contact points (all good) --> test idle without the MAF plugged in --> same rough idle and knock

The car knows the MAF is being plugged in because it does temporarily correct the idle when I plug it in as the engine is running, but it quickly reverts back to the rough idle and knock shortly after.

Any other ideas?

 

have you tried wiggling the MAF wiring to see if there is a poor connection.

Z

PS I hate to beat this dead horse, but are you keeping the car on a battery tender when it’s not being driven ?

Slightly low battery voltage can and will cause all types of strange engine behaviors.

 

Hi there,
It might sound silly, but can you use a multi-meter/power probe to check the ohms of resistance, as well as voltages, and amps in both MAFs? From what you describe, it sounds like the new MAF doesn't make a difference with the knock (you said reinstall old MAF, reset ECU --> rough idle and knock are still present). Unlikely perhaps, but I've had some third party parts come broken (especially if it isn't OEM or from the dealer)

And the connector you checked, I presume it's the following one: MAFS: MASS AIR FLOW SENSOR PI35 / 5-WAY YAZAKI 0902 / BLACK ENGINE COMPARTMENT / REARWARD OF AIR CLEANER. You can set up a multi-meter in serial to ensure the MAF is getting power effectively. As well, I would recommend running a live feed with your OBD scan tool, and checking the fuel mixture ratios and fuel PRESSURE when you hear the knock. It could be some fuel injector cleaner is needed.

Lastly, how did you previously check for leaks, did you use a leak tester/or soapy water all across on your intake manifold/PCV hose? Have you verified they are all gone?

 

Piston slap...whats the milage ? what oil ? use 10w 40 because the noise goes away when its real cold. Age of vehicle? Older ones need oil level raising 1 quart ( 6mm). Get a mechanics stethoscope to pin it down.Does not affect the idle on mine.
Put your location in the box top right so we know if you are F or C $ or £ or if you live down the road.

 

I've added a battery tender and unfortunately it didn't change my results.

I've since purchased three additional MAF's and none have changed my results.

I tested by hooking up a shop vac (set to blow, not suck) to the air intake and spraying with soapy water. All leaks have been sealed.

75k miles and 10w 30 oil. It's an 1999

 

Unfortunately the problem has progressed to full misfires (p0300 & p1316). Since the misfires began, I've-

• Replaced all coil packs w/ new (and tested outside the block to show sparks)
• Replaced all spark plugs w/ new
• Tested the Air Sensor fuse/relay
• Swapped around fuel injectors

Nothing has changed... I'm losing my mind here on trying to find the cause. The only other two items I am considering would be the ECU or a slipped timing chain (it has the old tensioners still). I'm VERY hesitant to pull the valve covers to check the chains because it took me two sets of valve covers and three gasket sets to get the damn things to stop leaking oil.

 

Hi there,

I happen to agree with Pistnbroke & zray, but you haven't answered our previous questions.

Let's shelve the the idea about timing tensioners.
Failing timing tensioners would've been apparent last time you took the covers off. If you want, you can use a mechanic's inspection scope to look at them just through the oil filler cap. I doubt your engine would run, it would be already destroyed if the tensioner is really broke. Your original video shows a knock, not a timing chain rattle anyhow. Why did you change the plugs and coils? Did you verify with a multi-meter they are bad? Scientifically, if you switch a bunch of things at the same time, it's really tough to help you. This problem started with codes attributable to the MAF, no?

Please, rather than switching a bunch of parts in the hopes that it will be one of them, please check your assumptions. There's really only three areas to consider which I've learned from flight school, fuel, air, and spark. You need to check all three of these assumptions without changing the rest of the variables. It honestly sounds like the MAF is the key we need to consider first. Plus, the computer doesn't know the engine is making sounds, so unless you take a mechanic's stethoscope to narrow the sound, it's possible you have multiple problems at once, possibly related (oil viscosity and temperature can cause this sound). What I want you to focus on is the data, the things we know for a fact from the OBD codes. Fact: Your engine was running rich and lean.

FUEL:

What is your fuel mixture ratio and fuel PRESSURE? You can get fuel mixture from your OBD reader. This is basically controlled by the computer, which uses data from the MAF. Attach a pressure meter to the lines running to the injectors to gauge pressure. Can you squirt some starter fluid into the air-box to see if the knock varies at all? Did you clean your fuel injectors?

AIR:

What are your voltages for your MAF? Do they align with the table I sent you? Again, what is your fuel to air mixture ratio?

SPARK:

Did you try wiggling the MAF wiring to see if there is a poor connection? It doesn't matter if the MAF is good or not, if the wiring is bad, it may misbehave. For a failing ECU, it can be instantly verified with a multi-meter (you can test the leads to it, ground, 5v/12v, as well as open it up, and test the circuits inside). No guess work is necessary. Also, how old is your battery? Have you tested it with a load bearing tester at start? Honestly, if it's old, or if it's low on charge, this can definitely cause a car to run rough on start-up.


Let us know what you find.

 

Hey Dayton- Firstly I just want to say how much I appreciate you taking the time write such a thorough response. I’ve gone through and tested what I can, and answered appropriately (I hope). All in all, my fuel pressure is awfully low 3.5 psi and my A/F ratio is 15.8-17 (I think?).

EDIT- I changed out the fuel filter and the fuel pressure has been restored (40 psi). My A/F ratio is averaging around 13.5. Unfortunately this changed nothing regarding my problem and I’m still getting the random misfires (p0300) and sensors errors (p0102, p0112).

Sorry I’m located in the US. I don’t normally keep the battery on a tender, but the car gets (or used to) driven regularly and it’s been on a tender since it’s been parked with these issues. The current battery is less than a year old and is showing a voltage of around 12.6 when tested with a multimeter.

The tensioners were just something I brought up because I felt out of suspects. I checked the tensioners when I had the covers off and they were fine at the time, but that was about 1k miles ago. Good to know, though.

I thought I had diagnosed a bad coil pack. I originally had a misfire on #4, so tested the coil pack (I tried finding a method to testing with a multimeter, but came up short since these coils have 4 prongs. In the end I pulled the fuel pump fuse, pulled the spark plug, grounded the plug and turned the engine over and saw no spark). I then swapped coil packs for #4 and #2, and then #2 was showing no spark but #4 had one. I figured I might as well replace all coil packs and plugs at that point given their mileage. After all was said and done and I realized I was still having missfires, I tested the “bad” coil again it was working all of a sudden… But yes, this I ASSUME all started with the MAF.

Is the “A/F Actual” reading my air/fuel mixture? If so, it’s jumping between 15.8 and 17.

The fuel pressure from the Schrader valve on the rail shows 3.5 psi, and holds for 10+ minutes. Shouldn’t this be 35-40 psi?? The fuel pump was replaced within the past couple years, but the filter was not.

Starter fluid in the air-box doesn’t seem to effect the knock at all. Fuel injectors were cleaned, and gaskets replaced, about two years ago.

I’m having some difficulty understanding the table, so I need to do some homework on how to test that (and read it) properly. But with the IGNITION ON, my MAF plug readings (from left to right) shows 12.28v, G, N/A, 3.99v, G. At IDLE I get: 14.12v, G, N/A, 4v, G

I’ve tried wiggling the MAF and nothing changes. I do get a dramatic change by unplugged the MAF, though. I’m little lost again in regards to what you explain regarding the ECU testing, so I’m going to add that to my homework list to figure out what to do there.

Again, thank you for your help so far!

 

Sure sounds like a hardware issue. Better check those tensioners.

 

FOLLOW UP for anyone that comes across this thread in the future - Turns out it was one of the chain pensioners that broke, leading to a stretched the timing chain and misfires on one side. I wasted A LOT of time and money thinking a stretched timing chain would have more severe results... don't make my same mistake!

 

I must say your engine sounds very noisy (ignoring the slap) compared to mine which is like a sewing machine with its 10w40 oil .
Can you say which tensioner broke ? The one on the long run or where .
Thanks