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Excessive Fuel Flow, Fuel distribution concern

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Well-Known Member
Apr 21, 2010
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My mechanic and I are discussing the reason for a high fuel flow. My Cherokee is a 1969 with the O-360-A4A engine and at about 50 hours SMOH. I installed an EI MVP-50 engine analyzer on the plane when I refurbished the plane last year. I am seeing the same trends all the time, so this has been an issue since I got it out of the shop last October. The trends are showing that I have a fuel distribution issue, #4 appears to be rich and #3 appears to be lean. Last Saturday, I attempted to lean the engine and try to run LOP. I have been reading all the LOP posts and thought I would give it a try. Several observations:
1. As I leaned the engine, I would have thought I would see a rise in RPM, but did not.
2. When leaning, I was watching the analyzer to see peak EGT and about the time I hit peak EGT, the engine started running rough and sure enough it was #3 cylinder that was the highest. All cylinders did peak about the same time.
When I looked at the trend, when the EGT's peaked, the RPM dropped.
3. I looked at the HP chart in the POH and verified it with the Lycoming book along with the reading on the MVP. They all showed that I was running 66-68% Hp. I was at 3500ft, OAT wa 53F and my fuel flow was 11.5-12 GPH. I should have been around 8-8.5 gph from what I could tell.
4. When I fill-up, the amount I put in the plane matches really close to the fuel used based on fuel flow, so that confirms the fuel flow is correct.
5. On takeoff, my Hp peaks at about 88% and I am seeing a fuel flow of about 16 gph. On the minimum allowable flow chart, it shows a flow of 13 gph. I would assume this is a flow with the engine leaned in cruise.
6. The plane climbs well at 800+fpm at Vy.
7. Climbing out at Vy, I can only do that for a few minutes and have to drop the nose and climb at 100 mph due to #3 CHT.

We are thinking that there may be an induction leak that is causing the fuel imbalance.

I guess the questions I am posing are:
1. Is there anyone measuring fuel flow on their 180? If so, does it seem like it matches the book values pretty close?
2. Do you see any EGT and/or CHT spreads that look like flow imbalances?
3. When leaning, are you actually able to run LOP? I remember seeing someone say their engine is getting rough as they reach peak EGT as I am seeing, but don't remember what kind of plane it was on.
4. On takeoff, what kind of fuel flows are you seeing? By the 0.1-0.11 gph/Hp, I should see a flow of 15.7-17.5 gph, which looks pretty close for 88%
5. What kind of Hp are you seeing on takeoff?

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