1997 Mercury 200 EFI Misses Intermittently

[mac18]

Definitely random

[jtipton91]

Save yourself the headache. Get the ecu checked out. I spent a whole summer dicking around with it only to find out it was the ecu. Same problems mine had. Intermittent lack of power. Loose drivers in the ecu

[mac18]

Hez and jtipton91 thanks for the input, seems like an ECU problem with the jerky and irregular stop/start nature of the missing and bogging down

[Hez]

Hez and jtipton91 thanks for the input, seems like an ECU problem with the jerky and irregular stop/start nature of the missing and bogging down

The place that my mechanic sent it to has a policy where they will check it to confirm diagnosis before rebuilding the ECU, then only charge a small fee if diagnostic check comes back good. ECU rebuild cost me $700 and was told he uses beefier drivers than stock.

[EuropeanAM]

With it being "random", you can just about count on it being electrical in nature.

Connections, switchboxes, cannon-plug connector, trigger harness, ECU drivers, coils, plug wires, spark plugs, etc.

[Takeum]

I’d start replacing the engines on board fuel lines,, with everybody using Ethanol these days, it collapses the fuel line from inside,,,my 97 merc 200 did exact same thing,,,always would start to bog down and like run out of fuel,,,then start and be fine,, come to find out when I removed fuel lines, I couldn’t even blow through one of them,the line that was bad was the one from the fuel filter to the VST …,,so I changed them all and Bingo,,,all was good

[EuropeanAM]

I’d start replacing the engines on board fuel lines,, with everybody using Ethanol these days, it collapses the fuel line from inside,,,my 97 merc 200 did exact same thing,,,always would start to bog down and like run out of fuel,,,then start and be fine,, come to find out when I removed fuel lines, I couldn’t even blow through one of them,the line that was bad was the one from the fuel filter to the VST …,,so I changed them all and Bingo,,,all was good

Better Yet, follow the FAQ Section Post: "Fuel Lines and Performance Problems" exactly as recommended.

[mac18]

Thanks Don and Takeum, I will have to start testing and eliminating potential sources of the problem. It's going to take me a while to recover from surgery and get back at it. Have a good holiday.

[mac18]

Additionally, take a real close look at the TRIGGER harness. Look for deterioration of the wiring, or the sleeve the wires run in.

You can do a resistance test on the trigger- during each connection/test, move the throttle from idle to WOT and back to idle (slowly) several times, while monitoring for any significant changes (which could indicate a compromised trigger lead/wire).

I was finally able to test the trigger harness. The 3 resistance readings were 1162, 1181, and 1161 ohms all in spec. When I moved the throttle slowly through its entire range the resistance readings stayed within +/- 50 ohms. No corrosion, worn wires/insulation so looks like the trigger checks out fine.
I also did a compression test following the procedures exactly as described in the FAQ sticky. The cylinder pressures in order were 119, 120, 128, 122, 105, and 120 psi. I squirted a small amount of oil in the #5 cylinder which was 105 psi and retested the compression. It quickly reached 127 psi. So can I assume the piston rings are worn in that cylinder?
While the engine was warming up I put a timing light on all the plug wires and all the cylinders seem to fire at regular intervals except #5 which showed some irregularity. After the compression test was complete I fired the engine back up for 10 minutes on the hose watching the #5 plug wire fire and it never skipped a beat. Looks like I will have to keeptesting to get to the root of the missing issue and have discovered a new problem with the #5 cylinder.

[EuropeanAM]

You're likely on the right track now.

[mac18]

Finally able to get back to working on this motor. I sent the ECU off for testing/repair but it checked out good with no problems. I am now going to remove the detonation controller and idle stabilizer module. Went through the procedure in the shop manual to verify that the .462 inch timing mark is calibrated using the dial indicator and it was dead on. The control arm link rod was 11/16" and the throttle cam was aligned correctly. Disconnected the ECU and white/black lead from the idle stabilizer and checked static timing. The idle timing was 4 and the maximum timing was 16 which is what the decal on my plastic flywheel cover specifies. The decal also says "timing will electrically advance to 22 BTDC with knock sensor connected". So should I set the maximum timing to 23 on this motor (OG570955) like is so often recommended? Can either of these two modules cause intermittent failure like I am experiencing? Thanks!

[JOE54]

yes ,and yes

[mac18]

Thank you Joe.

[mac18]

After removing the idle stabilizer and detonation controller, I took the boat out to the river for an hour and put it through its paces. It ran great without a single miss or hesitation. Since this problem has been so intermittent I wouldn't be surprised if this ordeal is still not over but maybe it is fixed. While setting the max timing to 23, I noticed there was water pooling up under the port cylinder bank . It appeared to be coming from the bottom of the #6 cylinder area. A recent compression test showed cylinder pressures in order #1 through #6 to be 119, 120, 128, 122, 105, and 120 psi. When I pull off the head covers to replace the gaskets is there anything I can do with the #5 cylinder that showed a compression of 105 psi? I am not willing to go for having a shop do a complete rebuild on this motor and have been considering a repower. Maybe the starboard cylinder bank has a head gasket leak too that doesn't show on the outside.

[leonreno]

May have a leak in the exhaust/adapter plate gasket. Do you have a water pressure gauge? Sometimes an exhaust or cylinder head gasket leak will show with a fast pulsing reading on the water pressure gauge.

[EuropeanAM]

Would help if you could narrow down whether the leak is between the cylinder head and block, at the exhaust divider plate, OR between the powerhead and adapter plate.

Removing the wrong one and replacing it won't help the water leak...

In reference to your question on the #5 cylinder, a leaking head gasket is POSSIBLE (removal/inspection is the best way to know for absolute certainty).

As suggested above, there are other possible symptoms that may (or may not) be present, such as pulsing water pressure, high water pressure, or even very clean spark plug in that particular cylinder.

[mac18]

Would help if you could narrow down whether the leak is between the cylinder head and block, at the exhaust divider plate, OR between the powerhead and adapter plate.

Removing the wrong one and replacing it won't help the water leak...

In reference to your question on the #5 cylinder, a leaking head gasket is POSSIBLE (removal/inspection is the best way to know for absolute certainty).

As suggested above, there are other possible symptoms that may (or may not) be present, such as pulsing water pressure, high water pressure, or even very clean spark plug in that particular cylinder.

Thanks Don. The leak I can see on the port side is coming from between the cylinder head and the block directly below the #6 plug. Does the fact that squirting a small amount of oil into the #5 cylinder and immediately seeing the compression jump from 105 to 127 psi point strongly to a problem with the rings or could the oil also quickly cover up a gasket failure that is not visible?

[mac18]

Leon I do have a water pressure gauge but I am not sure it is working right. I will look into verifying whether it is working correctly or try and get one for testing. Thanks for the input

[EuropeanAM]

Thanks Don. The leak I can see on the port side is coming from between the cylinder head and the block directly below the #6 plug. Does the fact that squirting a small amount of oil into the #5 cylinder and immediately seeing the compression jump from 105 to 127 psi point strongly to a problem with the rings or could the oil also quickly cover up a gasket failure that is not visible?

More likely to be a piston ring problem (OR a cylinder that is DRY from inadequate fuel delivery).

[mac18]

Just put the motor on the hose in the driveway to check the water pressure. Reading about 1.5 to 2.5 psi idling at 750 rpm, around 3 psi at 1000 rpm, around 5 psi at 1400 rpm and 6-7 psi at 2000 rpm. The readings did show a noticeable fast pulse, especially at 2000 rpm.