In reading I didn't notice where you re-checked fuel pressure after your fuel rail was only showing 20psi with key on - Replaced both fuel pumps. Now instead of no start, I had hard start.
Re-check fuel pressure both on the low psi side and the high side. You'll want to ensure you're now not...
^ Gotcha to where in further studying, you're correct.
I did find one other note that brings up a past memory to some of my earlier thoughts above, (Many fuel pumps are used on similar engines. In order to identify the correct fuel pump for your application, you must check the “clock” position...
There are/were two designs for the fuel pump...One up one down and searching through the two pump designs in the parts catalog, the one that goes down suggests line modifications would be necessary so either make your own or possibly buy what's available under the facing down pump parts catalog...
0A617689 belongs to a MERCRUISER 140, model number 01402006 which makes it a 1986 year model.
https://www.mercruiserparts.com/140-gm-181-i-l4-1982-1986-6229718-thru-0b450800
0A637671 = MERCRUISER MC1 1.98:1, model number 01989016.. 1986 as well...
I wouldn't be surprised if Merc had even a newer version by now and looking up the serial number in question seems to first suggest it's pointing to use number 28 but starting in January of 2022, they have a supplement part number 8M0185811 which ought to help with any updates even over 28 and...
Seemingly seems a bit unusual giving issues being the engine is cold but odder things do tend to happen unexpectedly being a boat.
Glad you stayed with it to find the solution…
How did you come to the conclusion it’s a TKS diode issue?
https://yanmarshop.com/catalog/media/F53DEL3GOJSW4Y3INVQXE2LOMUXW2ZLENFQS6YTNMUXUOQKZIRBVQQSRI5JE6RCFJVBFCR22J5CUWVCTG5DUCMSBFZYGIZQ
See item numbers 7…. Might need your engine serial number to fine tune the correct part but in general you ought to be able to buy a new or used one probably on eBay using the part number...
Take a jumper wire at the back of the key switch and connect terminals B and A, then take another jumper wire and connect to terminal B and touch terminal S (Start) and see if the engine starts normal.
Also right now, when you turn the key to just on (ignition) do the gauges power up? No? Then...
Here's your parts catalog for your serial numbers...
0B849523 = https://www.mercruiserparts.com/3-0l-gm-181-i-l4-1987-1989-0b450801-thru-0c856558
0B934426 = https://www.mercruiserparts.com/r-mr-alpha-one-sterndrive-1983-1990-6225577-thru-0f386995
^One in the same as,
0B943249 =...
Wondering if someone’s been switching wires at the key switch as the colors seem off to me unless I’m going colorblind in my old age ha ha… the colors seems backwards between the I and A.
