The reason for #3 miss

[93festiva]

We changed engines on the weekend, here's the reason for the #3 miss. Seems there was a definate lack of compreesion in that hole.



Bill

Note piece of exhaust valve that is missing.

[ejp2fast]

i have had very bad luck with the #3 cylinder on the B3... on my 91 efi B3, the exhaust valve had a large chunk out of it ... and on my 88 carbie B3 the #3 cylinder has literally 0-5 psi compression, and I'd put money down on that exhaust valve, as the head is not off yet.

not sure whats up with B3 #3 cylinders!!!

[Zanzer]

I was just talking with Kartracer about this the other day. We've both noticed how cylinder 3 tends to be the first to check out on many of the cars we've worked on.

Here's the exhaust valve on the engine I pulled from my 93 about 2 months ago.

[Larry Hampton]

On a Dodge 2.2 or 2.5, it's the #4 cylinder. The T-stat housing is between the #3 & #4 cylinders, so #4 doesn't get as good of cooling action. Turbo guys will plate the stock location and move it up to the back of the head so you get a full cross flow.

[kartracer46]

It is common for almost every 1.3 I have torn down. 80-90% are in need of exhaust valves. Don't usually see to many that bad off, but they are tuff little engines that will run even with what some consider to be catastophic failure.

[Zanzer]

Mine wouldn't have looked that bad if I hadn't driven it like that for almost 18 months LOL :mrgreen:


Hey, it still got 33mpg which is better than anything else I own

[Christ]

18 months is roughly 18000 miles, at 33mpg, 546 gallons of fuel. At 40mpg, 450 gallons, a difference of 96 gallons. Assuming fuel was $2.50 at the time, it cost you an additional $240 in fuel to ignore the problem, at best. It might have cost $100 to fix it, netting you $140 additional savings.

Food for thought.

On suzuki 3 cylinder engines, and to some extent with the honda insight, the egr system is to blame for cylinder/vale failure. Could that be the case here?

[Zanzer]

Maybe...but it was way cheaper than the 17-19 mpg in my Mustang and F-150 so in the long run I was still saving money. And I wasn't exactly ignoring the problem. When I have 4+ cars sitting in line at a time that are paying customers, that tends to take precedence over my car so I had to wait for some down time to fix it.

[getnpsi]

I go thru 2 tires every 8-9 months in my srt-4...driving normally. At 120 bucks a tire getting my festiva on the road isnt just for fuel savings. I can get free used tires in 13s from time to time. No one gives away 17s until they are not worth mounting

[getnpsi]

You think those bad valves are from a condition over time or just one hot event?

[Zanzer]

I'm going to say it's a function of time. At least on my car anyway. My B3 slowly developed the miss and it wasn't a case where it ran fine one day and not the next. Exhaust valves in a B3 really take a beating. Most valve jobs I've done on these heads have been due to the exhaust valves having tons of carbon build up on them and not sealing properly. When I pull the head apart the intake valves usually look pretty good for the mileage (they're cooled by the incoming air) but you can see where the exhaust valves have taken the heat and the seats are typically very pitted. B3's and first gen B6's have the worst exhaust runner design I've ever seen and some of the valve failures may have something to do with this. I've been doing quick port jobs on the exhaust side to help with flow in an effort to see if it helps remedy the problem but I can't verify any improvements until the cars get quite a few more miles on them.

A few other things I've noticed:

The exhaust guides are typically worn out which can cause the valve to improperly seat and/or bounce around and flex. This isn't good for it. Plus the valve dissipates a lot of heat through the seat so if it's covered in carbon and isn't seating properly it will be operating at a higher temperature and more prone to failure.

Many times the heads I work on don't have the best casting quality. There tends to be a good bit of flash, edges, and imperfections. This can lead to a hot spot in the head and can also cause detonation.

Other factors could be improper ignition timing, an engine that runs hotter due to poor cooling from a weak water pump, lazy T-stat, clogged radiator, and a lean condition due to improper mixture. The last 2 cars I've worked on had the wire to the O2 sensor broken. A broken wire or a sensor with excessive miles can mess with AFR.

[Christ]

Something that happened all at once would generally have a more pronounced appearance when you look at the problem. A broken part of a valve, rather than a melted section covered in carbon.

However, I have seen an engine run "fine" with bent rods, but one day, it just quit on the highway.

Seemingly a "single event" that caused it, but the stress indications on the rods showed that they'd been bent for quite some time, and only recently couldn't build enough compression to keep the engine running.