1989 Merc 2.5 200EFI issues

[hchi]

I have been working on a friends 1991 (corrected year) 200 Merc EFI (Serial Number OD068759). My friend said he can get the boat to start by giving it throttle upon start and prior to getting on plane, he said he had to rev the motor to 3500 rpms in neutral 8-10 times. After that he could get the boat to rev up and get up on plane. The boat is not idling correctly and having a hard time starting. He brought it over and i was thinking the switch boxes or stator and trigger could be bad. It has fresh fuel, did a compression check all six wire about 110 +/- 4, fuel pressure at 35 psi, spark is good in all six cylinders. As i was checking everything out, I disconnected the the 2 brown/black wires on the port side temp sensor and found the TPS sensor was way out of spec. Closed it was at .640 and I adjusted the TPS at .250 when closed. I also checked the manifold temperature sensor. I saw it the impedance move up in down in the shade and hot sun, but have no clue where it should be at. After the TPS was adjusted it fired up and ran smooth with no misfires. He took it strait out to the water and it ran fine. The next morning, same issue, it would not stay started and die about 2-4 seconds after cranking. I'm going to do another check and if the TPS is not holding at .250 when closed, I'm thinking it is bad. The issues is that it is a $600 part now. Another thing i was thinking could it be the ECU? Any thoughts.

[JOE54]

sure could be/ TPS normaly runs bad dont die as with head temp sens and air temp sens

[hchi]

Took a second look at it today. TPS was not too bad, it was tested at .240 this morning. Was set at .250 last night, looks like TPS is ok. Went and checked the grounds and the air temperature sensor again. Unmounted ECU and checked the hose for the manifold pressure hose. Still holds pressure and gave it a quick clean with carb cleaner. Put it back together and it fired, but would not hold idle until I throttled it a few times. I have a new temp sensor coming in for manifold and port side head. Idle fine on following starts.

[hchi]

Friend gave it a start this morning and it fired up no problem. We have to wait about a week or so for the heat wave to past. Early mornings in CA this week is lower 80's. By mid week it should drop back to the upper 60's in the early AM. Will have to try a cold start during that time.

[JOE54]

hope it gets in 60s here all day yesterrday on lake 103 index 111

[hchi]

Thanks for your help Joe. My friend did another run today in his Champion bass boat and it ran fine. The best improvement came after the manifold pressure sensor was cleaned. He is still out there in the heat fishing now! 0645AM it was 81 degrees out here. Normally it is upper 60's.

[hchi]

The gremlins came back! The boat would not idle and would not plane. Boat would not turn over 2500 RPMS. He brought the boat back by and we fired it up on the hose. It idles but it seemed a little rough but not bad. Cleaned the ECU contacts and was check all the grounds. Found one ground that did not look to good by the idle control module. Unbolted it and one of the green wires weren't fully plugged in and it popped out. Replaced the ground wire and plugged the green wire back in (snapped in place). It ran fine again, hoping the problem is resolved? I know most people say get rid of the module and it is useless.

[hchi]

Just an update. The port side temp sensor and the manifold temp sensor finally came in over the weekend. Installed them pretty quick and gave the motor a quick visual inspection. Found a small hose that had a cut on it. It is one of the two small hoses that sit on top of the VSt tank and I think they go into the manifold. Wonder if this would cause unmetered air and part of the intermittent issues? Anyone know what those beed lines or lines are for?

Today my friend took his Champion out and he had no issues with the cold start or hole shot. He is taking it for a quick run and to see if he has a surge or loss of power issue. I'll report back in a bit.

thanks,

[JOE54]

ONE is for vst over flow ,ONE is for bleed system to dump fuel oil mix back into vst, and yes it could let air or fuel in when its not suppose to be, what else sir, good luck