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Prop Job

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When coming around the base turn and pulling the throttle towards idle I get a slight engine stumble below ~9.5" MAP accompanied by the #2 EGT dropping to ~600 while the other three remain around 1100. The engine is a parallel valve IO-360-A1A at 8.5:1 compression with Airflow Performance injection and constant speed Hartzel. The injectors are new .028's, the #2 plugs have been swapped with #1, and the flow divider and fuel controller have been recently overhauled. Anyone have any ideas?

Alex
 
An intake leak normally causes the EGT on the affected cylinder to go high, not low. EGT going low could mean the cylinder is not firing and developing the heat that the others are seeing.

Electronics International has a great troubleshooting manual that they provide for free. Here's a link. http://buy-ei.com/
 
GAMI check

Run a GAMI spread and see if they are all peaking at the same fuel flow, if you've done this before you will have a base line to compare with. It sure sounds like an intake leak. Once you pull the throttle closed air begins leaking because of the big delta P. Id look at the tubes in the sump for proper crimps and the gasket at the cylinder.
Good luck.
Tim
 
Bubblehead said:
An intake leak normally causes the EGT on the affected cylinder to go high, not low. EGT going low could mean the cylinder is not firing and developing the heat that the others are seeing...[/URL]
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Except the subject engine is fuel injected. It will run fine at large throttle openings, but a localized intake leak will cause the cylinder to lean out so much at low throttle that it will stop firing - in other words, it's going extremely lean of peak - I.e. Cold.
 
Bubblehead said:
An intake leak normally causes the EGT on the affected cylinder to go high, not low. EGT going low could mean the cylinder is not firing and developing the heat that the others are seeing.
Click to expand...

Nice reference!

If the idle mixture was not rich to begin with, the leaning due to an intake leak could drive A/F beyond lean firing limit and misfire.

There may not be a single issue contributing to this condition.
 
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Toolbuilder - I agree, if the leak were huge it would go way lean and not fire, but I would think if the leak were that big the problem would show up in even higher power settings.

Also, to do the induction leak test correctly you'd want to start out rich at say 23" then reduce throttle to 13" so that you know you're starting on the rich side and the leak would lean it out and raise EGT.

At one time I had intake leak problems due to some bad o-rings on the intake tubes. I started doing the induction leak test frequently so can speak from first hand experience that the EGT goes up BUT the affected cylinder was still firing. It was not so lean that there was not a combustible mixture in the cylinder.
 
I had an intake tube fail on the sump side of a 200 HP (Lycoming "cold air")- it sucked the whole oring boss/fitting down the tube toward the trumpet, thereby opening a massive hole in the induction tract. Engine ran fine at WOT; but that cylinder went cold on downwind.

I will agree that the EGT in an induction leak will initially go high as it leans, but will eventually go LOP and cool off - it may even quit entirely. It's possible the OP does not notice any unusual EGT until this particular power setting. And in this case, the engine may be well past the peak event. It would also be expected that this cylinder would quit entirely at idle.

I'm also not certain the OP has this problem, but it sounds like it to me, and it will take about 5 minutes to verify visually.

When troubleshooting, take the easiest/most likely approach first. These intake gaskets are notoriously failure prone... I'd pull the tube and look at the gasket.
 
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Thanks for all the input guys. I'll check the induction tubing on #2 this afternoon. I replaced the intake gaskets last fall during the cond insp but will check it again.
 
Prop Job said:
I replaced the intake gaskets last fall during the cond insp but will check it again.
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This could be important. It is difficult to get the tube with o-ring and gasket lined up so it mates flush with the cylinder. The thin flange on the upper end of the tube can crack if slightly cocked when the bolts are tightened.

When you say "intake gaskets" are you talking just about the gasket at the cylinder or the o-ring at the sump too? Check the o-ring closely. Sometimes they get a small cut on them that spoils the sealing ability. I think I mentioned this before but will reiterate. I had several o-rings delaminate and in once case a portion of the o-ring was missing.

Just out of curiosity, why did you replace the gaskets at the last condition inspection?
 
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