Merc 200 XRi ECU Replaced, Now What TPI Setting to Use?

I have a 1991 Mercury 200 XRi SN 0D014703 on my old Skeeter bass boat. My current TPI setting is 0.305 V, which seems well above the factory repair manual's recommended starting point of 0.135 +/- 0.010 V and maximum recommended 0.250 V. I'm having some engine problems, so I'd like to reset the TPI as part of my troubleshooting process. But there's a possible hitch...

Some years ago the original ECU died, and the repair shop replaced it with a repaired ECU, PN 824003A 8.

Does this ECU require a different TPI setting than the original ECU, and, if so, what is it?

Many thanks.

2.4L and 2.5L ECU use different TPI voltage values. 1991 was the changeover year. Which is yours?

its sets at .0250

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Originally Posted by pyro

2.4L and 2.5L ECU use different TPI voltage values. 1991 was the changeover year. Which is yours?

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Per original post, this is a 1991 200 XRi 2.5L serial number 0D014703.

I was under the impression that this 1991 engine might have been sort of a one-of-a-kind with regards to the ECU and maybe other gadgets, and that's why I thought I'd should verify what the new ECU would be expecting. I think the new ECU was used in '96-'98 model years.

Thanks for responding.

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Originally Posted by TEXAS20225

its sets at .0250

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Thanks, but don't you mean 0.250 V?

its a quarter of a volt!!!! set it with mercs tpi harness with digital volt meter set on 2 volts there is a process you wont get very far without having a mercury manual on these things its full of information (not a seloc or clymers junk but a mercury manual ) they are all over the net the 91 motor had a short production life as 7 petal carb fishing motas aint too easy to maintain did not take merc long to figure it out it also has the very small exhaust chest its highly overrated

I have an early edition of the 1991 factory service manual. It has tons of good info, but it sure could be organized better!

I set the TPI to 0.250 V per the manual with the head temp sensor unplugged using my digital VOM, but is it safe to assume this value is the same for the much later repaired ECU, PN 824003A 8?

It is the same for all Laser EFI's after you set the TPS voltage leave the temp sensor disconnected and slowly open the throttle watching the voltage. Should increase with the throttle opening and end up somewhere around .468V. at wide open. if the voltage does not increase with throttle opening you TPS has issues.
Have you done a complete link and sync as well?

Dave

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Originally Posted by Dave Strong

It is the same for all Laser EFI's after you set the TPS voltage leave the temp sensor disconnected and slowly open the throttle watching the voltage. Should increase with the throttle opening and end up somewhere around .468V. at wide open. if the voltage does not increase with throttle opening you TPS has issues.
Have you done a complete link and sync as well?

Dave

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Yes, I have sync'd the throttle cam with the throttle arm and am working on timing.

My original question relates to tuneup steps I have done to try to diagnose and fix a rough idle and transition problem. Good compression, good spark, good fuel system operation (after fuel pump kit and new racer fuel line and OEM primer bulb). I have concluded that I need to pull the injectors and send them out to be cleaned, and I will also change out the reeds and work over the reed blocks. (Injectors have never been cleaned and only the second set of reeds! Not bad for a 25 year old engine I think!) If that doesn't make her run right I'll turn her over to someone more competent than me!

Many thanks for your suggestions and info gentlemen!

Not a bad idea to check that the resistance changes smoothly as the throttle is opened, they wear out usually at the partial throttle cruise position.

I also have a 1991 2.5L 200 and the TPS was worn out on it, Merc still sells them but they are expensive.

You can do the adjustment without the Merc tool, I just probed the wires with a small needle and connected the volt meter to them. Small dab of sealant will seal up the wires after your done, I used 4200 for the job.

harness cost 30.00 or so its good just to have one LOL

You don't need to poke holes in the wires or buy a $30 harness.

Strip some beefy stranded wire, several inches worth. Cut off several inches of individual copper strands, Bend the end of two strands over a half-inch into a tight "U" and stick each one into the female pin receiver side of the connector. (blue and orange wire? I seriously forgot!) bend the wire strands over the side of the connector boot and plug the connector together with the strands sticking out from under the boot. Wrap the strand ends around your tester leads.

You guys are good!!!

I had thoroughly researched S&F before doing my troubleshooting, so I had seen many of the related tips and discussions. I ended up using a couple of T-pins that I use for building RC airplanes to back-probe the connector at the tan and blue wire terminals. I used wire-clip leads on my DVM and measured the DC voltage throughout the throttle range. I was very relieved to find that the TPI didn't have any dead or noisy spots. These TPI's are just rheostats, and it's SHAMEFUL the price Mercury asks for them. The same device for a care is one-tenth the cost.

Right now, I'm preparing to extract the fuel injectors and the reeds. That should keep a retired guy busy for a bit!

Thanks for everyone's advice.

Hey Duper, You are correct about the shameful price Merc charges for those TPi's. It's highway robbery!!!! I cant believe someone in the aftermarket has not done something with these. Like you I'm retired, old electrician, and stuff like that just blows hell out of my budget. Not that I need one, although I do have a '93 200 XRi. Makes me want to get the catalog out and find a rheostat with the right spec and size to replace one..... I wonder???? Oh well, who are you sending your injectors to? I need to do that my self sometime this summer and get the boat ready for the coast this fall.....

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Originally Posted by rutro

Hey Duper, You are correct about the shameful price Merc charges for those TPi's. It's highway robbery!!!! I cant believe someone in the aftermarket has not done something with these. Like you I'm retired, old electrician, and stuff like that just blows hell out of my budget. Not that I need one, although I do have a '93 200 XRi. Makes me want to get the catalog out and find a rheostat with the right spec and size to replace one..... I wonder???? Oh well, who are you sending your injectors to? I need to do that my self sometime this summer and get the boat ready for the coast this fall.....

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Rutro, I have also wondered if there isn't a TPI in an automotive application that could be used. It does seem that could be a big opportunity for aftermarket TPI's just like there is for CDI modules, triggers, stators, ect. In fact, I already did some research. Seems that a corporation named CTS (http://www.ctscorp.com/automotive/se...clesensors.htm ) is one of the leaders. Couldn't seem the find a part to fit the Merc though!

The TPI for my 2003 Tahoe is only $80 at Autozone. The TPI for my 200 XRi is like $450!!! Just doesn't seem right! (Don't anybody give me this "cost of development" line, because this is not technology that Mercury developed!)