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low EGT at idle after start

blaplante

Well Known Member
Having just installed a JPI monitor on my 0-320-h2ad (with Bendix FI), I started up today to check that all is working. I got some odd results - at idle, the EGT for #3 is MUCH lower than the other 3 cylinders. (Like less than half). As the engine was still pretty cold I don't have much info on CHT.

So, increased to about 1400 rpm. All 4 are sitting around 1100 degress CHT (I had leaned some after start). OK... back to idle. #3 went back to a quite low EGT. Repeated with the same results.

Eh? What's going on here? I doubt this is a probe problem given the temp difference changes with rpm.
Engine has about 260 hours (and 0.1 monitor time).

Some searches raised multiple theories:
low compression - was AOK at last annual, not many hours ago.
stuck/sticking valve
bad lifter or rocker on intake
bad valve spring
intake leak

Thoughts?

Thanks!
 
An intake leak would cause HIGHER EGT's. Have you looked at the ignition side? Wires/plugs/gaps?
Do check the idle mixture setting on the carb as well. At idle, slowly pull mixture to cutoff and verify you get about a 50 RPM rise.

Vic
 
Two things to look at:
- Stuck valve
- A chunk of junk in the spider blocking the tiny idle port for that cylinder. The easiest check for this is the shot glass fuel flow test.

Carl
 
Response

Note that this is fuel injection not carb. I can't figure out how the idle mixture setting on FI would cause a single cylinder mixture problem.

Regarding the spider - I would have thought that a blockage in a port on the spider would indeed cause low flow to that cylinder - which would be *worse* above idle (not better).

Thanks
 
Note that this is fuel injection not carb. I can't figure out how the idle mixture setting on FI would cause a single cylinder mixture problem.

Regarding the spider - I would have thought that a blockage in a port on the spider would indeed cause low flow to that cylinder - which would be *worse* above idle (not better).

Thanks

Nope - spiders do not work like that. As fuel flow goes up the diaphragm goes down exposing larger fuel ports. The idle port is small.

Do the shotglass test.

Carl
 
Here is the shot glass test result of a spider with a spec of junk in in.
Carl
3-DD35217-BB42-428-B-A211-E760-C7-EC6-ED1.jpg
 
Note that this is fuel injection not carb. I can't figure out how the idle mixture setting on FI would cause a single cylinder mixture problem.

Regarding the spider - I would have thought that a blockage in a port on the spider would indeed cause low flow to that cylinder - which would be *worse* above idle (not better).

Thanks

My bad. I saw O-320 and assumed carb.

Definitely look at the injectors. Pressure is very low at idle.

Vic
 
And the winner is...

Fuel injection distribution spider.

Thanks! The brain trust here saved me some airplane bucks!

-Bryan
 
Old thread but same problem...

So Bryan, did you find that #3 injector or line was blocked (resulting in lower EGT's) or #1,2 and 4 were blocked giving high EGT's???

Thanks! I'm having the same issue with my Continental IO360: #1 & #2 have low EGT at idle while #3-6 have much higher EGT but all even above idle.

Rich
 
Old thread but same problem...

So Bryan, did you find that #3 injector or line was blocked (resulting in lower EGT's) or #1,2 and 4 were blocked giving high EGT's???

Thanks! I'm having the same issue with my Continental IO360: #1 & #2 have low EGT at idle while #3-6 have much higher EGT but all even above idle.

Rich
Ha, resurrection of a 5 year old thread. There was partial blockage in the distribution spider (as I said above).
The blockage was in the slot (of the spider) for #3
The way this thing works in a Lycoming / Bendix is different than in a Continental.
 
Ha, resurrection of a 5 year old thread. There was partial blockage in the distribution spider (as I said above).
The blockage was in the slot (of the spider) for #3
The way this thing works in a Lycoming / Bendix is different than in a Continental.
Thank You! I've had the same issue on my Continental IO360 for some time now and my IA keeps saying there's no issue....Interesting that it started after I had the flow divider overhauled.
 
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