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1991 to 1997 7.4L Engine Swap

That happens here as well.....that's why I try to look things up BEFORE clicking the reply button...sometimes successful....sometimes not....
 
Okay I will change power wire on the electric choke to purple wire on the coil and report back later.

As for the alarm issue; I have a thermostat housing with two side mounted sensors/senders on each side of the housing. Starboard side has a solid Tan wire, port side has Tan w/blue stripe. I replaced the port side sensor (the porcelain part crumbled when removing the wire stud nut) with a Quicksilver 806490T water temp “sender”. Looking at a diagram now, it looks like one is considered a water temperature “Sensor” and the other is called a water temperature “Sender” ? I am wondering if the replacement sender is the wrong part, they did look different when I swapped them, I just figured it was the new replacement style.
 
Sender is for gauge.
Sensor is for alarm.

I dont believe the appearance makes a difference.
How they function does.
One is a switch (sensor)
The other is a variable resistor (sender)

Tan wire is sender

Tan with blue is sensor

Disconnect tan with blue and see if alarm still goes off.
If you short (touch) tan with blue to ground it will cause alarm.
 
Okay thanks for the clarification.

I disconnected the one I replaced (tan w/ blue stripe) and nothing changed, touching it to ground didn’t change either (alarm still sounding all the time).

I disconnected the other one (solid tan) sender wire and the temp gauge went to zero.

So I think I have two temp senders, instead of one sender and one sensor. Any idea what the part number would be? Neither sensor nor sender come up on the t-stat housing diagram. Original engine serial is 0D501133 (all accessories including t-stat house were transferred to new engine).

Or do you think something else is setting off the alarm?
 
I disconnected the knock sensor and the alarm stopped... From what I’ve heard, these rarely fail. What am I looking at here? I did move the location of the knock sensor from the old block to the new. It is T’d in with a water drain in the same side of the block as oil filter. Engine sounds normal to me. Only other thing is that there might be some gas in the oil from running it so rich before those adjustments so level may be a tad high. I do plan on changing oil and filter soon, after I test it out on the lake (been busy/rainy weather).
 
Doing a little more research. I typed in the engine serial number in the parts search, and I don’t see a knock sensor anywhere? It has the Tunderbolt IV ignition system which I don’t think has a knock sensor included.

So I don’t think that is a knock sensor, I think it’s a low oil pressure switch alarm? It’s tan w/ blue stripe.

It was originally right next to the oil pressure sender, which I believe is solid blue, and goes to the oil pressure dash gauge.

What is proper oil pressure?
 
I think I am kind of answering my own questions out loud. I believe it is the oil pressure alarm switch, and it’s screwed into the block with a water drain, and not into an oil passage. I will get some new fitting(s) and move it back over next to the oil pressure sender.
 
no knock sensor used with the TB-IV ignitions.....

If you oil pressure switch is screwed into the water jacket, it isn't doing what it is supposed to and the horn/buzzer will actuate....

It needs to screw into the oil galley to work correctly....and make sure you clean it out before reinstalling into the correct fitting...
 
lucasmahony said:
Drive oil level is good.
Click to expand...
Did you mean oil level is good or you verified the level sensor is working? Drive oil level can be good & level sensor can be broken setting off alarm.

but if your oil pressure switch is screwed into water jacket that's likely it. Where is it in the water jacket? Wires on my harness wouldn't be long enough to screw it into block water jacket and thread size is 1/8" vs 1/4" npt.
 
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Well with the engine running and alarm constant on, I unhooked the oil pressure alarm switch and the alarm stopped. The drive lube reservoir level is good so I’m assuming the level sensor is working fine, nothing was moved or unhooked from that during the engine swap. I am 99% certain I just need to move the oil alarm switch to an oil passage, and that it’s currently in a water jacket drain port.

Long story, but I had to add in a oil pressure safety shutoff switch for my new electric fuel pump, so I moved the original oil pressure alarm switch, and T’d the new oil pressure safety shutoff switch where the alarm switch was at (right next to the oil filter block mount) along-side the oil pressure gauge sender.

When I did all this, I thought/was told, that switch was a knock sensor, not realizing it was a low oil pressure alarm switch. So I thought it could be mounted anywhere on the block, so I bought some brass fittings and T’d that into a water jacket drain on the port side middle of the block.

I didn’t have any time to monkey with it yesterday but will tonight.
 
lucasmahony said:
Well with the engine running and alarm constant on, I unhooked the oil pressure alarm switch and the alarm stopped. The drive lube reservoir level is good so I’m assuming the level sensor is working fine, nothing was moved or unhooked from that during the engine swap. I am 99% certain I just need to move the oil alarm switch to an oil passage, and that it’s currently in a water jacket drain port.

Long story, but I had to add in a oil pressure safety shutoff switch for my new electric fuel pump, so I moved the original oil pressure alarm switch, and T’d the new oil pressure safety shutoff switch where the alarm switch was at (right next to the oil filter block mount) along-side the oil pressure gauge sender.

When I did all this, I thought/was told, that switch was a knock sensor, not realizing it was a low oil pressure alarm switch. So I thought it could be mounted anywhere on the block, so I bought some brass fittings and T’d that into a water jacket drain on the port side middle of the block.

I didn’t have any time to monkey with it yesterday but will tonight.
Click to expand...

Basically all you need to do at this point is Tee the oil safety shut off switch (for fuel pump) and the low oil pressure alarm switch.

That would be the simplest in my opinion.

Question?
Is the oil filter at bottom of block or is it extended and bracketed off the elbow?

All Big Blocks and small block MAG engines have an Extended oil filter and should be bracketed off the Exhaust elbow.

In the end it does not matter but that is how it comes from the factory.
 
lucasmahony said:
Long story, but I had to add in a oil pressure safety shutoff switch for my new electric fuel pump,
Click to expand...


Lucas, as you may know, the electric fuel pump's relay will be triggered by a N/O (normally open) style low oil pressure switch, and not by a N/C style, as per what may be used for a low oil pressure alarm system.
In other words, the N/O style will close during engine oil pressure, and will open in the absence of engine oil pressure.
Whereas the alarm switch will be open during engine oil pressure, and will close in the absence of engine oil pressure.
 
lucasmahony said:
Well with the engine running and alarm constant on, I unhooked the oil pressure alarm switch and the alarm stopped. The drive lube reservoir level is good so I’m assuming the level sensor is working fine, nothing was moved or unhooked from that during the engine swap. I am 99% certain I just need to move the oil alarm switch to an oil passage, and that it’s currently in a water jacket drain port.

Long story, but I had to add in a oil pressure safety shutoff switch for my new electric fuel pump, so I moved the original oil pressure alarm switch, and T’d the new oil pressure safety shutoff switch where the alarm switch was at (right next to the oil filter block mount) along-side the oil pressure gauge sender.

When I did all this, I thought/was told, that switch was a knock sensor, not realizing it was a low oil pressure alarm switch. So I thought it could be mounted anywhere on the block, so I bought some brass fittings and T’d that into a water jacket drain on the port side middle of the block.

I didn’t have any time to monkey with it yesterday but will tonight.
Click to expand...

Well that explains it, I think you need 4 psi to close the oil pressure switch which you won’t get with water in the jacket. As jack said just t it in by other oil switch and sender should be good. I think on my small block the fuel pump oil pressure switch is tapped into a plug on top of block by distributor
 
RicardoMarine said:
Lucas, as you may know, the electric fuel pump's relay will be triggered by a N/O (normally open) style low oil pressure switch, and not by a N/C style, as per what may be used for a low oil pressure alarm system.
In other words, the N/O style will close during engine oil pressure, and will open in the absence of engine oil pressure.
Whereas the alarm switch will be open during engine oil pressure, and will close in the absence of engine oil pressure.
Click to expand...

PCK,

In other words for product specific information,

the oil pressure switch is a two terminal- two wire connection (therefor it can only be used one way) So what type NO or NC does not matter.

The oil pressure alarm switch is a one wire connection (therefor it can only be used one way) So what type NO or NC does not matter.

Post count +1
 
the oil pressure switch is a two terminal- two wire connection (therefor it can only be used one way) So what type NO or NC does not matter.

The oil pressure alarm switch is a one wire connection (therefor it can only be used one way) So what type NO or NC does not matter.
Click to expand...


There are many different types of oil pressure switches out there. If the OP was to use the wrong one, his system will not work as intended.

normally open vs normally closed oil pressure switch.jpg
 
I appreciate all the responses and I do believe I have it figured out. This weekend I am planning on pulling her back out of the heated barn to run on muffs in the driveway and hopefully take a rest run on the lake. Supposed to be sunny and low 60°s. I will report back on how it goes.

Thanks again everyone, this forum is great.
 
o2batsea said:
Why not show a pic of the required switch, a link from our host's catalog page or something equally useful.
http://www.marineengine.com/newparts/part_details.php?pnum=MER87-805605A+1
Click to expand...

Yes, that would be great.
However, the switch (p/n 87-805605A 1) that you linked us to, is a single pole, N/O switch used to take a circuit to Negative for use with a LOP alarm.
For an electric fuel pump (as alluded to in post #47), the OP needs a 2 pole N/O LOP switch.

That was my point for showing the different types.
 
Product specific post: This should end switch discussion.

If using a Carburetor with an electric fuel pump. Use this oil pressure switch (TWO WIRE) This is the current replacement for Mercruiser replacing older models.

http://www.marineengine.com/newparts/part_details.php?pnum=MER87-864252A01

87864252A01.jpg

If using EFI/TBI and they come with electric fuel pumps and an ECM, A single post/wire switch is used as it provides an input to ECM. (Oil pressure, yes or no)


http://www.marineengine.com/newparts/part_details.php?pnum=MER87-805605A+1

87805605A1.jpg
 
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