Figure this out

[J-Mech]

I'm going to take full advantage of the general talk area. I want to give you guys a problem I ran into this week and see if you can figure it out. Call it a game, whatever. This happened on a car, but we'll pretend it's a Cub, just so it's less intimidating. Just because, let's say it's a Cyclops 2182 (3cyl Kubota, because then the engine is similar to a car). Hope at least someone plays.

Rules:
You can ask any question, and I'll tell you the answer that I found.

History:
~None. Brand new to the owner. Bought off individual, no questions asked. Discovered the problem after bringing it home. I figured out it had been on fire at one point, so electrical problems are a possibility. Also appeared that the engine had been apart somewhat recently. (Newer looking gasket on the timing cover, only one I could see easily.)

Problem:
~Won't idle. Seems to get worse the warmer the engine.
~Runs decent above idle, but lacks power/ weak acceleration. (Customer didn't realize it, but it did.)
~Misfire (Most noticeable at idle.)

Initial findings:
~Running rich
~Low vacuum at idle
~Confirmed ignition misfire.


What problem do you address first?
What's the first step?

[cubby102]

Can we ask the make model and engine? Computer controlled or carbureted? Since you stated it looked as if the timing cover was opened up. Possibly didn't get the timing set in correctly? Just guesses I'm not good at this game I like stuff to be sittin in front of me...

[J-Mech]

1998 Pontiac Sunfire
2.4L 4cylinder DOHC

Chain driven timing, chain driven water pump.

Codes revealed engine misfire, idle control problem

Data stream showed negative fuel trim on short and long term, low MAP reading, but low 02 with very slow to respond on post cat o2 sensor

Mentioned the gasket only because I noticed it, but head was dirty, so was the cover. I thought it may have been changed because of an oil leak. Also, it was near the apparent fire damage. But no evidence suggesting it was recently worked on. Most OEM GM gaskets are black, this one was blue.

[tech1979]

I had one like what you are describing a while back the intake gasket was leaking. You can use a benzo propane torch to test it by spraying under the intake runners. Just chased my tail a couple of months ago on the same problem.

[J-Mech]

Very good! Your thinking vacuum leak, as did I. So, I used a mechanical gauge to confirm the MAP reading. 10" mercury at idle. Both the mechanical gauge and MAP matched. Now, I figured I should be able to hear a 10" vac leak. Thats huge! But I head nothing. Plus IAC position showed it open quite a bit. Visual inspection confirmed. It did not have any vacuum leaks.

Keep em coming!


Under edit: tech1979, I see that's your first post, but your not a new member. Thanks for posting and playing along! Keep the ideas coming!

[Berwil]

The J-mech puzzler, do I just post my answer here or do I send it in on a $20 bill?

Originally Posted by J-Mech

I'm going to take full advantage of the general talk area. I want to give you guys a problem I ran into this week and see if you can figure it out. Call it a game, whatever. This happened on a car, but we'll pretend it's a Cub, just so it's less intimidating. Just because, let's say it's a Cyclops 2182 (3cyl Kubota, because then the engine is similar to a car). Hope at least someone plays.

Rules:
You can ask any question, and I'll tell you the answer that I found.

History:
~None. Brand new to the owner. Bought off individual, no questions asked. Discovered the problem after bringing it home. I figured out it had been on fire at one point, so electrical problems are a possibility. Also appeared that the engine had been apart somewhat recently. (Newer looking gasket on the timing cover, only one I could see easily.)

Good obfuscation, the history part is definitely a red herring.

Problem:
~Won't idle. Seems to get worse the warmer the engine.
~Runs decent above idle, but lacks power/ weak acceleration. (Customer didn't realize it, but it did.)
~Misfire (Most noticeable at idle.)

Initial findings:
~Running rich
~Low vacuum at idle
~Confirmed ignition misfire.


What problem do you address first?
What's the first step?

I have no idea, I figure it's something silly like reconnect the pcv valve or clear an exhaust restriction. I mostly just wanted to post some Car Talk references.

Bill

[J-Mech]

Bill, I prefer you send in your response with non-presidential bills.


Your exhaust idea is good!
Convince me why I need to check the exhaust for full credit.


Can't believe no one went after the easy problem first...... I always do easy first.

[J-Mech]

If your not a car guy, here's what we just determined:

Engine is still missing, and still running rich (the computer is trying to lean it out). The choke (IAC) is open and doing it's job. No vacuum leaks (which technically would cause a lean condition) but is is low on vacuum. Still won't idle, just stumbles until it dies. At this point there is no evidence to support the carb (fuel injectors) are over-fueling.

[Shrewcub]

Random ignition misfires? Any codes? Compression readings?

Clogged cat from misfires or possibly cam timing is what I am going with until I know the answers to my questions.

Oh how bad was the fire? Could the cat have gotten hot enough to start the fire?

[J-Mech]

Random misfire: yes
Codes: nothing pertinent or helpful, so ill just say no

Fire was centered at the fuel rail. Most noticeable damage at injector harness. No, cat was not the source of the fire.

Compression..... good question! I checked compression. Cranking, all plugs out, throttle plate full open: 225 psi on all 4. (Too high, agreed?)

After that, I decided plugged exhaust. Dropped pipe at manifold (before the cat). No change. All symptoms still present.