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I've joined the engine misfire club

1213 Views 6 Replies 4 Participants Last post by  GermanGuy
Couple of days ago driving home, engine started missing at highway speeds. Then got worse and CEL came on and flashed too. Seemed to get worse if I slightly let up on the throttle. I got her back home and scanned the codes with a handheld scanner (reads VW codes). Car is a 2004 , 1.8T AWM motor, currently at 119,000 miles.

I got:

17536, Fuel Trim Bank1 System too Lean

16684 : multiple misfires detected,

along with each cylinder misfire, codes 16684 thru 16688

MAF was replaced about 30k miles ago, coils have 79,000 miles on them, plugs have 34,000 miles on them. Popping the airbox cover noticed SAI hose from airbox to pump was in two pieces. Other than that have not looked much around the engine compartment.

I was planning on doing some maintenance this spring before this happened so I already have: 2.0T coils, adapters and plugs. 034 Silicone PVC kit (and other related bits), MAF (bought and then not needed awhile back), SAI air hose.

Been doing a lot of hours at work, so I will not be able to look at the car until the weekend. Dad is letting me use his second car.
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It's leaning out for some reason, maybe an air leak after the MAF, or maybe low fuel pressure. The air leak is more likely, so start taking a careful look at the whole induction system, from the duct leaving the air box, to the hose connection at the throttle body. Also, look at any hoses and check valves leading to the intake manifold. You may have to pressurize the intake path to find the leak, if there is one. This can be done by using common PVC pipe plugs of the appropriate sizes, from the hardware store. One plug needs a Schrader (tire inflater) valve to allow your tire pump to pressurize, but carefully so as not to exceed say 20 PSI.
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I had similar issues codes, checked all hoses and check valves for leaks. That didn't do it and moved on to N80 vacuum purge valve near intake assy. Take solenoid hoses apart from both ends, disconnect plug then directly test off battery. Do momentary contacts to battery to see it opens closes each time VDC applied. These can get sticky and throw codes. Also seems to be issue on fuel fill ups where you go to start car immediately after and is hard starting. Cost me $40 at Oreillys.
Since it gets worse when you let off on the throttle, my money is on a vac leak, since that would tend to leak more under high vacuum, which is what happens when you reduce throttle.
I was leaning towards the vacuum leak too. Sat I woke up at noon after working 12 hr shift to 4 am ( yay, 2nd shift). It was snowing and the garage was cold. Did a look around the engine bay, using mirrors and flashlight didn't see anything. Got cold, went inside grumpy and tired from the nite before.

Started looking around on vac leak detection, seeing smoke machines, etc. Didn't want to set anything up like that up, I wanted quick and easy. I was going to attempt to pressurize the system with about 10 psi of air, figured with the compressor running there would be no way to hear the air leak. I had a spray bottle that I was going to fill up with soapy water, it had spray or stream setting on it. Too late and too tired, I at least had a plan of attack for Sunday.

Sunday comes and the sun was shining, I got the compressor ready, filled up the spray bottle and off to the garage I went. I thought I would do another visual check of the vacuum and very gently wiggled the various connections, what did I see? Focus on the suction jet pump

Back to work now on removing that piece, fun with those once time clamps.

Done, problem solved. The L shaped pipe from the suction jet pump to the intake was very clean. For those of you servicing the PVC, normal?
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Yep, that's a very common way for the SJP to fail. Did you just glue it together for now? The part has since been updated to be much sturdier, so replace it when you have a chance.

For me, the entire SJP was clean as a proverbial whistle when it failed.
Already replaced, that was one of the "extra" parts I already had for the PVC maintenance planned.
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