1994 850NA Cylinder misfire MVSOLVED bad manifold gasket

Post by **boerence** » 17 Oct 2015, 18:04

Hi, I hope someone has some good advice. 1994 Volvo 850 non-turbo automatic 197,000 miles. At idle the car shakes excessively so started investigating.

Car idles rough but seems fine when driving it. By unclipping injector plugs I determined cylinder No. 1 (closest to passenger side) isn't firing as there is no change when I unhook it, whereas the engine chugs severely if I unplug any of the other injectors. I have several other 850's to swap parts with. All the other cars work fine with the parts I swapped from this car.

Here's what I've done: Swapped then replaced plugs with Volvo OEM's. Swapped plug wires. Removed injectors and cleaned them, and put them back in a different order. Listened to injectors with a stethoscope and they all 'click'. Swapped distributor cap and rotor. Swapped MAF. Checked cylinder pressure - all between 180 and 185 psi. Checked fuel pressure (with a tire gauge) 40 to 45 psi. Checked codes and there weren't any. Checked all the vacuum lines and the PCV system pulls negative pressure.

If I rev the engine to 2000 rpm or so and unplug injector No.1 there is a slight difference, but if I unplug any of the other injectors there is a pronounced chugging so it seems like cylinder No. 1 is firing at least partially at higher rpm no load, but not as strong as the others. I thought about switching fuel pump but based on the fuel pressure don't think that's the problem. Gas mileage seems fairly normal.

Anyone have any thoughts? Thank you!

Post by **Ozark Lee** » 17 Oct 2015, 19:09

Perhaps a wire loom problem. Is the #1 injector trying to fire? You can just stick your finger on it and feel it pulse. Also compare the way it feels when it fires to the other injectors. The injectors should have a crisp snap sort of feel to them when they fire. If the #1 feels duller it could still be clogged.

If you get no pulse at all then it is a wiring problem. All of the injectors fire at the same time on a '94 N/A so it should be an easy fix if it is wiring.

...Lee

Post by **erikv11** » 17 Oct 2015, 19:51

Alas, this could be a burnt exhaust valve in cylinder #1. I suggest you check the compression.

Post by **boerence** » 17 Oct 2015, 20:12

Thanks for the tip Lee. So you're saying that all the injectors pulse at the same time? If that's true could I switch the wires from injectors 1 and 2, and then if it's No. 2 that doesn't fire (using the wire for No. 1) that would pinpoint the problem as being in the loom. I did inspect the wires as far as I could and saw no visual problems.

erikv11, as stated, I did a compression test and cylinder No. 1 was the same as the other four. If the exhaust valve were burnt I would assume there would be no compression on that cylinder. Correct?

Post by **erikv11** » 17 Oct 2015, 20:13

Oops - I even went back up and scanned the OP but I just did not see the compression test mentioned. But I do now ... you are right, there is no danger of valve trouble.

The test you suggest about switching around the injector plugs is a good one, go for it.

Post by **cn90** » 17 Oct 2015, 21:09

Mark the wires at the distributor cap (photo in forum or the web).
Now INTENTIONALLY swap the #1 connector with a nearby connector.
Start engine, if the problem moves to another cylinder then the high-tension wire is bad (visual inspection can be deceptive).

At that mileage close to 200K, a new set of Bougicord is highly recommended (do NOT use another other brand).

Post by **abscate** » 18 Oct 2015, 04:04

I think you have eliminated everything except the number one fuel injector wiring loom.

You could back plane the electrical connectors to test voltage but I think I would go back trace the wires and look for breaks since you have to do this anyway to repair.

Nice troubleshooting acumen !

Post by **boerence** » 18 Oct 2015, 09:16

Thanks everyone for your advice. Knowing all the injectors fire at the same time is very helpful. I started the car and pulled off injector plug 1 - barely perceptible change, basically no change. Then I pulled off injector plug #2 (of course engine sputtered on 3 cylinders) and plugged No. 1 onto No. 2, and that brought it right back to where it was. So I don't think there is a problem with the wiring.

Pulled off rail, tested injector with my homemade syringe pump, and it squirts just fine - also tested another one and it was just the same. So I don't think injectors are the problem.

Looked inside the manifold through the injector holes and there's something funny going on at the very left side of the manifold at cylinder No. 1 - I think the manifold might have a crack in it although I can't see any on the visible portion of the outside of it (see photo, if it attached). I need to get a bore light and get a better look at it. That might be the problem - I checked my stash of parts but no intake manifold - didn't think I would ever need one I guess.

Post by **cn90** » 18 Oct 2015, 10:20

Never mind what I said above, it is not a good method for testing (wrong firing sequence).

Post by **boerence** » 01 Nov 2015, 05:21

Just in case any one is interested I finally replaced the intake manifold gasket and that fixed my missing at idle issue! My last ditch effort worked.

From the looks of it the old gasket was leaking very slightly on cylinder no. 1. On four of the cylinders the gasket was evenly pressed and centered, but on cylinder no. 1 the gasket hole was off-centered, and there was a 'new' forced bolt hole next to where the punched gasket bolt hole.

The gasket was obviously installed incorrectly somewhere along the line. I've put around 100k on the car - now good for another 100k, right?

I tried to add some pictures.

Thanks again to everyone who tried to help!

: Cylinder no. 1 above pen note offcenter compared to no. 2; 1.jpg (373.92 KiB) Viewed 1466 times

: Backside if cylinder no. 1 gasket; back.jpg (408.05 KiB) Viewed 1466 times