200 efi seriously lacking top end performance, timing issue, tps?

[cichlidfish]

Hello!

Engine is a 2000, 200 Mercury efi, Serial Number: OT157051

I am having some problems where I am lacking about 600 rpm of wide open throttle (only getting 5200), when I used to run 5800 with the same setup. Low end is fine and boat gets on pad fine, it's just sluggish top end and lacking rpm. Things I have checked:

-Compression is uniform 114 across the board
-Fuel Pressure is 36-37 psi at idle and full throttle, and after key off holds pressure
-Spark test while running, and timing light flashes consistently on each cylinder on the water.
-dropped gear case and exhaust tuner is firmly attached and there are no exhaust restrictions

I am new to checking/ adjusting timing but I have the manual and performed the whole sync and link procedure. When doing the Maximum timing procedure I was confused by the part that says "ECM remains disconnected for maximum timing adjustment"?? Is that the big plug for the ECU, Confused about where the ECM harness plug is?

Heres what I did:
-Confirmed timing pointer using dial indicator at 0.462
-Ground spark plugs
-disconnected fuel

The static results I got were about 4 ATCD for idle, and maximum static timing was 20 BTDC. I think the manual states this motor should be 24 BTDC on static test. Could this 4 degree retarded timing account for this much RPM loss at full throttle??

The only other thing I can think to check after timing would be the TPS but I've heard only a mercury tech could check that properly.

I appreciate it!
Turner

[JOE54]

timming is critical on these engines , yes , air temp sensor will kill it also, as well as broken reed

[silverbullet02]

4 degrees won't make that kind of difference. TPS is easy to check with a regular volt meter, unhook the temp sensor and I forget which 2 of the 3 wires you gotta poke, done it a hundred times and always have to poke around myself, lol. Did you verify you're actually getting wide open throttle? The ecm is the big plug coming off the computer with a twist lock nut on it.

[cichlidfish]

I did verify the linkage on the motor is actually getting full throttle, and it all looks good to me and butterflies are fully open. Yeah, I’m hesitant to believe that 4° of timing could have that significant as an effect as well. And that’s good to know about the TPS, I will try to figure out which prongs to poke at and look at the specs on that Have you ever heard of the TPS creating a problem like mine?

[cichlidfish]

Update: tested tps using the "wire in plug trick" and it tested perfectly within the manual specs. So that's not the problem. Also, is it correct that the ECU does need disconnected during full throttle static timing test?

[silverbullet02]

Update: tested tps using the "wire in plug trick" and it tested perfectly within the manual specs. So that's not the problem. Also, is it correct that the ECU does need disconnected during full throttle static timing test?

If you unplug the ecu it won't squirt fuel and try to start.

[EuropeanAM]

+1

Especially when plugs 2-6 are out and those wires are on a spark tester (or grounded).

[cichlidfish]

Sounds like a recipe for some burnt hair haha, I had just unhooked the fuel pump. Some people mentioned unhooking the spark stabilizer box too but it’s not in the manual. I’ll advance that timing up to 23-24 and see if it makes any difference at all.

[cichlidfish]

Update, brought timing up to 23 degrees at static full throttle, and it made no noticeable difference on the water. Any other ideas?? This problem started after a fresh rebuild so maybe it’s just a weaker motor and the builder messed something up.

[leonreno]

We have seen/read on here of builders putting in the pistons on the wrong side or the piton sleeves installed or slipped in the cylinder blocking ports.

[JOE54]

i was on vacation years ago ( probly in deep east texas hunting the elusive wookalar ) when a customer of mine lost a piston in a 200 efi he had it repaired at brand x shop replaced powerhead he broke it in started using it and noticed a 3-4 hunid loss in rpm after many trips back to x i get the privilege of finding problem the powerhead used was a 150 block after very much debate with x they learned all blocks are not the same , VERIFY you have a 200 block /powerhead and yes that the pistons are in correctly and yes it did cost him more the second time

[cichlidfish]

Haha I had that same thought and I did verify that it is a 200 block. Short of tearing the thing down I don’t know what else to check, I haven’t performed a leak down test yet so that’s probably my next move. I guess I’m wondering if I should run it the way it is or get rid of this thing before it blows up again if it was built incorrectly in some way. Motor builder is MIA

[EuropeanAM]

Just to double-check: You've confirmed that the butterflies (all) are achieving HORIZONTAL in their bores at WOT position? There's an adjustment screw on the block that would have changed with a powerhead change....

[cichlidfish]

Just to double-check: You've confirmed that the butterflies (all) are achieving HORIZONTAL in their bores at WOT position? There's an adjustment screw on the block that would have changed with a powerhead change....

I have checked that all of the butterflies are opening perfectly horizontal and the rest of the linkages look to be perfectly set up. The fuel injectors were flow tested when the motor was built so that’s the only thing I haven’t really checked, but it’s strange that the motor runs perfectly fine and even gets on pad faster than the old one did, it’s just lacking so much too end power.

[leonreno]

Have you checked the spark plugs after running it? I would try and make a long high speed run and then stop and pull plugs and check them. Sounds to me you are possibly missing the power of one cylinder for whatever reason.

[cichlidfish]

Have you checked the spark plugs after running it? I would try and make a long high speed run and then stop and pull plugs and check them. Sounds to me you are possibly missing the power of one cylinder for whatever reason.

I haven’t done a long run at full throttle but the next time I’m on the water, I will run a long hard run at full throttle and then kill it right away and pull the plugs. I pulled the plugs after a hard run at my lake and they looked super uniform to me but I had a bit of an idle after that one. The few times I’ve done it they have been perfectly tan in color.

[cichlidfish]

I also just did a leak down test and got the following results. The motor wasn’t probably completely at operating temp when I did it because I had some compressor issues but it was still warm.

1- 8%
2-3%
3- 8%
4-3%
5- 7%
6- 3%

not as good as I’d hope for a new build, but I don’t think those numbers would account for a 600 RPM loss haha.

[JOE54]

verified timing is comming up to spec at 5200 rpm under load in lake , test prop of low pitch and mabe small diameter can be used to do this at boat ramp on trailer

[cichlidfish]

verified timing is comming up to spec at 5200 rpm under load in lake , test prop of low pitch and mabe small diameter can be used to do this at boat ramp on trailer

I’ll give that a go, the boat is super slow now so I could have someone do it running normally hahaha