94 850 turbo Cyl 5 Misfire

[JimBee]

To pinpoint the hissing sound use a length of heater hose as a listening tube. A couple of feet works well. With one end to your ear, move the other end around the suspect area. You'll find it.

[IG-88A]

That's a good idea with the heater hose. I'm going to try that. Both of the misfire codes returned this afternoon, and the engine is idling like poo. I think I'll start with checking diligently for leaks, then swap the #5 injector, and then pull the intake manifold to investigate after that.

In response to an earlier question, my turbo gauge reads just below 1/4 when idling or coasting.

[IG-88A]

UPDATE- So I went to a junkyard this morning and got two new injectors, just in case one was bad. I also found two alter one 850s there. Nice. Went back home, cleaned up said injectors, and popped in the best looking of the two. I noticed there was no pressure to relieve at the Schrader valve. So, while I was in there, I noticed that the connection between the hard line and the elbow from the fuel pressure regulator to the vacuum tree was loose if connected at all. There was tons of play, and it just slipped in and out effortlessly. So I cable tied both the hard/soft line junction and the attachment at the tree. Reassembled, cleared the codes, and started it up hoping for the best. Idle was still stumbly and weird, so I tried disconnecting the MAF. The car immediately died, so I don't think the MAF is part of the problem. I decided to drive to an independent Euro mechanic that fortunately is just about a mile away. They told me they couldn't get me in until Wednesday, so I decided to go ahead and drive to work. I'm happy to report that the ECU seems to have corrected the stumbly idle and the misfire code hasn't returned after a 30 minute drive. Another thing, my 315 EVAP code hasn't returned yet either. So, I may have got lucky in finding that FPR line in the shape it was. When I arrived, I did notice a 232 and 233 for fuel and air trim, but I think that must be from disconnecting the MAF and IAC to see if I noticed anything. Fingers crossed, fellas. I hope that was all it was. I'm still puzzled though about how that FPR connection being loose would have caused a misfire only in cylinder 5. If anyone has any clue on that, I'm interested in hearing an explanation. My only theory would be that injector 5 is at the end of the line, so the other four were drinking it all up while 5 starved. If it really is fixed now, I'm anxious to see if I can finally get decent gas mileage. If I go code-free for a week, I'd like to mark this solved.

Oh, and JimBee, I tried using the heater hose to more easily locate the hissing sound. When I put the free end on on the upper IAC hose (which is brand new, and silicone) , it was super loud. I never got that kind of volume anywhere else I tried it.

[erikv11]

For the record: disconnect the MAF with the car off, then start it up. It will probably always die if you disconnect the MAF on a running vehicle. It will stumble at startup too, until the ECU goes into default air:fuel mode.

Hopefully it is fixed!

[IG-88A]

Oops. Thanks for the clarification, erik. Hopefully I didn't screw anything up while doing that.

Okay, so I guess it can never really be so simple. I leave for lunch, excited to get a chance to drive around in the newly fixed car for a few, and I get a stumbling idle at startup again. I let it run for a few, and it finally smooths out somewhat. But it still feels rougher than it did on the way in, so I check the codes after going to grab a bite to eat. Probably about 15 minutes drive time. Now the 232 idle code is back. I've never had this code before today. So now I'm not sure what's going on. Maybe by shoring up the connection between the FPR and the vacuum tree, I've exposed the next weakest link in the chain.The misfire code and EVAP code haven't returned yet, so that's good news, but now I've got this one. Hmm.

[erikv11]

FYI That FPR connection is there primarily to regulate pressure under boost, to a lesser extent under vacuum. Without a proper connection, the fuel pressure will be lower than expected under boost and the car could be running lean. At idle a poor connection should have almost no effect on FPR function, possibly the car could run a little rich. It's good you got it fixed.

232 does sound like a vacuum leak, did you check the little elbow/connection on the passenger end of the intake manifold?

[IG-88A]

Hmm. That's interesting. Do you think that could have inadvertently caused the misfire somehow? It's just so odd that it never popped up before, and still hasn't come back since I repaired it today?

Since mine is a '94, it doesn't have that little elbow. When I first got the car, I hunted all over for that thing after hearing so much about it, until finally realizing that it didn't exist. Instead, that vacuum line goes into the intake manifold just under the vacuum tree. I did some spraying with brake cleaner tonight and got idle to raise all over the place in the front area of the engine. I've got a leak, or multiples somewhere. Maybe my manifold gasket isn't good after all. I bought a new vacuum tree and O-ring when I serviced the PCV, as well as a new throttle body gasket, but maybe those aren't seated fully. No clue. It's funny how one thing leads to another on this thing lately. I just need daylight and another actual day off to sort this out. Maybe I'll still take it to the independent shop, just for the convenience of the diagnosis. Then I can make repairs over the weekend.

[IG-88A]

So the misfire code came back yesterday on my way to work. I caved in and took it to the independent shop this morning. I never did have any luck finding the vacuum leak that seemed to be around the throttle body somewhere, even though I made sure the intake and TB bolts were snug and all clamps and hoses in the general area were secure. This could end up being my intake manifold gasket after all. I figured if anything, the mechanic would find the issue and just offer to patch things up, which I was prepared to let him do. So no more than two hours later, I get a call from his wife saying that the problem is in the head, and my best bet would be to give up on it or buy a remanufactured head. Not once did I get to talk to him to find out what diagnostic steps he took in determining this. Now I'm wondering if he even did anything but start it up. And as luck would have it, they're leaving before I get off work today, so I won't get a chance to ask him personally. I just can't justify disturbing the head, and I don't even know how that could be considered the culprit, with the close compression values I got over the weekend. I put a call out to an acquaintance of mine who specialized in VWs for a long time. Turns out he knows a Volvo tech and he's going to put him in touch with me. A second opinion is in order.

[erikv11]

I agree, that just doesn't sound right. Let us know what the second opinion is, my curiosity is piqued.

[rspi]

He likely did a compression test and leak down to determine the problem.