Need help diagnosing engine problem

[walkman]

Help, I'm stumped!

Background. 2004 RV-8. I purchased in early Feb this year with approx 800 SNEW. Superior XP-360 with Bendix RSA-5 injection system. Engine now has approx 1,000 hours. No purge valve. Engine originally had 2 Slick mags, about 300 hours each, with Tempest massive electrode plugs. I replaced one mag with an EFII EI system, I have also replaced the Holley fuel injection pump with an EFII boot pump module. Compressions at pre-purchase all high 70's. No significant issues with oil analysis performed every change since new including one I just did a month or so ago. I'm running 100LL.

Problem. When engine is hot, I get a VERY lopey, rough idle. It will idle for a second or two at 1,000 or wherever I set it, then the idle will drop out down 800 or lower for a second, then back up to 1,000. It feels like a cylinder is dropping out for a second then coming back online, but I see no indication in the EGT/CHT to identify if this is in fact the case or identify which cylinder. Problem seems to be worse the hotter the engine is. When its hot I get a lot of sputtering, occasional backfire, and sometimes feels like its almost about to quit.

The airplane did not do this when I picked it up, it has gradually gotten worse as the year has progressed (and the WX has gotten warmer?). Problem did NOT suddenly start with either the pump or the EI upgrades.

The engine does make good power and performs well in the air.

What I have done:
-2 new sets of automotive plugs - no difference
-cleaned gaped ohmed out all aviation plugs (900-1k ohms) no difference
-mag is dead nuts on 25 BTDC
-all ignition leads are in ex cond.
-problem does not change when running on mag, EI, or both anyway
-problem does not change when fuel pump on or off (pump works properly)
-problem doesn't change with different mixtures on the ground
-for a few seconds after a cold start runs rough them smooths out, but.....
-checked all exhaust valves and all valve springs, no broken springs, all valves smooth as silk, no sticking, and just the tiniest bit of wobble (no dial gauge but seems fine)
-all new intake gaskets and hoses/clamps - no change

I'm stumped. I'm going to try the "clear tube" test and see if I'm somehow getting air in the fuel lines, clean all my fuel filters and strainers, and double check all the adjustments on the fuel servo this weekend.

Any guesses?

Here's a short video showing the behavior. I'm not touching the throttle.

[Mike H]

Have you tried adjusting the idle circuit? Here is a link to some quick trouble shooting info.
http://occonline.occ.cccd.edu/online...n%20Servos.pdf

[walkman]

Originally Posted by Mike H

Have you tried adjusting the idle circuit? Here is a link to some quick trouble shooting info.
http://occonline.occ.cccd.edu/online...n%20Servos.pdf

Thanks for the link. I have the Bendix/RSA manuals that this is a reformat from. I plan on going through this, this weekend.

[Mike H]

Sounds like you have it under control. Let us know aht you find.

[rhill]

The Backfire sounds like electrical.May I ask, key or toggle switches?Any common grounds?I wouldn't rule anything out with the fuel system yet,just saying.
RHill

[walkman]

Originally Posted by rhill

The Backfire sounds like electrical.May I ask, key or toggle switches?Any common grounds?I wouldn't rule anything out with the fuel system yet,just saying.
RHill

Originally ACS key switch when it was dual mags. Now toggle switches for master/alt (DPST), EI (potter switch breaker), Mag/start (DPDT On-off-(on))

[Mike H]

Ignition shutting off intermittently may casue afterfiring, but I doubt it will cause backfiring, they are two very different occurences with different causes. I would think if it were ignition related you would see other symtoms besides a erratic idle. I would start looking for induction leaks and idle mixture setting.

[lr172]

Originally Posted by Mike H

Ignition shutting off intermittently may casue afterfiring, but I doubt it will cause backfiring, they are two very different occurences with different causes. I would think if it were ignition related you would see other symtoms besides a erratic idle. I would start looking for induction leaks and idle mixture setting.

+1

I would go no further until I was sure the idle mixture was set properly. Induction leaks are included here, as they impact the mixture. You can also have someone watch the exhaust as you drop to idle. Any puffs of black smoke would indicate you are going rich, but I am guessing that you are going lean. A partially plugged injector could also cause one cylinder to go lean, but you would probably notice differences in the EGTs.

Larry

[rocketbob]

If it doesn't happen cold you are getting vapor lock. 100LL will also vapor lock especially if the lines aren't insulated and kept away from radiant exhaust heat. A gascolator FWF will make it worse particularly Van's POS blue gascolator since it does not have a standpipe.

[walkman]

Originally Posted by Mike H

Ignition shutting off intermittently may casue afterfiring, but I doubt it will cause backfiring, they are two very different occurences with different causes. I would think if it were ignition related you would see other symtoms besides a erratic idle. I would start looking for induction leaks and idle mixture setting.

Backfiring isn't usual, its happened once or twice. Pretty sure I've eliminated ignition as a source anyway, as the problem manifests itself equally when running either or both ignition systems.

I've replaced all intake gaskets, hoses, and clamps with new. Not sure where else there could be a leak of unmetered air.