mercruiser 7.4 (L29) firing order

[1990dtgl98]

Hey everyone.

I have a 1999 mercruiser 7.4 (L29) engine in my sea ray that I've been having issues with.

Part of the problem was a backfire thst was persistent and low power. I replaced the plugs and coil and rewired it, now it won't fire off.

I was using the mercruiser manual:



My plug and distributor looks like this:



So going by that I routed all my wires the following way.



But now she won't even fire, much less misfire. I don't see anything about rotation in the manual. Is there something I'm missing?

 

[dubs283]

have you checked for good consistent spark at the coil lead?

 

[dwco5051]

have you checked for good consistent spark at the coil lead?

Could be something simple like an pulled lanyard for the safety kill switch. Did you pull the distributor or have anything else off. Need a little more info on what been checked up to now.

 

[1990dtgl98]

have you checked for good consistent spark at the coil lead?

Yes. I actually went back to the previous coil that was in when the boat ran (but misfired).

Could the previous owner have installed the rotor 180*?

 

[1990dtgl98]

Could be something simple like an pulled lanyard for the safety kill switch. Need a little more info.

Could be something simple like an pulled lanyard for the safety kill switch. Did you pull the distributor or have anything else off. Need a little more info on what been checked up to now.

Distributor has not been off. Pulled wires and plugs and put new ones on. Then reran all the wires as the manual stated.

Knowing I was replacing the wires I didn't check the order they were in when I pulled them off the cap. Just figured I would go by the service manual.

 

[dubs283]

Yes. I actually went back to the previous coil that was in when the boat ran (but misfired).

Could the previous owner have installed the rotor 180*?

okay, but did you actually verify good consistent spark?

would be next to impossible to install the rotor 180 off

have you inspected under the distributor cap? usually when replacing the plugs its a good idea to r and r the cap/rotor as well

 

[tpenfield]

It looks very different than my 1996 (gen 6) wire layout, although the firing order is the same as what you have. Did you verify the position of the rotor inside the distributor with the engine at #1 TDC on the compression stroke?

 

[tpenfield]

Here are the approximate locations on my Gen 6 454 (shown in green)

 

[1990dtgl98]

okay, but did you actually verify good consistent spark?

would be next to impossible to install the rotor 180 off

have you inspected under the distributor cap? usually when replacing the plugs its a good idea to r and r the cap/rotor as well

I used a inline tester and had spark on all points.

I did put an order in for a cap and rotor. Figure I might as well do that now.

 

[tpenfield]

@1990dtgl98 I think you were responding to a prior post while I was posting my replies . . . just want to make sure you saw them above . .

 

[dubs283]

I used a inline tester and had spark on all points.

okay, seeing as how you didn't check the firing order on the old wires there's the possibility that you may not have connected the #1 wire to the proper post.

best course of action is to pull the cap, verify TDC #1 compression, note rotor rotation, then you can attach the leads accordingly

keep in mind you will need at least a service mode plug at the diagnostic harness lead to properly time the ignition

 

[1990dtgl98]

@1990dtgl98 I think you were responding to a prior post while I was posting my replies . . . just want to make sure you saw them above . .

I did yours seems completely opposite of mine.

 

[tpenfield]

My engines run . . . Not sure if you have checked the position of the rotor at #1 TDC

 

[1990dtgl98]

okay, seeing as how you didn't check the firing order on the old wires there's the possibility that you may not have connected the #1 wire to the proper post.

best course of action is to pull the cap, verify TDC #1 compression, note rotor rotation, then you can attach the leads accordingly

keep in mind you will need at least a service mode plug at the diagnostic harness lead to properly time the ignition

I guess my concern was if they previous owner had it set on tdc for exhaust the rotor could be 180* from where it should be.

 

[1990dtgl98]

My engines run . . . Not sure if you have checked the position of the rotor at #1 TDC

I have not. But if im going to pull it off I might as well replace the cap and rotor while I'm there

 

[dubs283]

I guess my concern was if they previous owner had it set on tdc for exhaust the rotor could be 180* from where it should be.

engine would not run if the distributor was out 180

 

[1990dtgl98]

Maybe I'm

engine would not run if the distributor was out 180

Maybe I'm having a brain fart.

But my manual shows #8 as the rear most (toward the transom) point on the distributor. Tpen and other quick searches online show #8 as the front most pin. I'm wondering why they're esentially opposites.

 

[Bondo]

Maybe I'm

Maybe I'm having a brain fart.

But my manual shows #8 as the rear most (toward the transom) point on the distributor. Tpen and other quick searches online show #8 as the front most pin. I'm wondering why they're esentially opposites.

Ayuh,..... You need to bring #1 cylinder to Tdc, compression stroke,.....
The #1 on the distributor cap is whichever post the rotor is pointed at,.....
There's no particular post that has to be #1, like in the pictures,....

 

[Bt Doctur]

You cannot go by that if the dist was clocked differently. #1 can be anywhere o n the cap depending on how the dist was previously installed. You could try removing #1 plug and dist cap. crank engine listening for the rush of air from #1` and looking to where the rotor is pointing

 

[1990dtgl98]

Gotcha. Looks like I'll be waiting till my cap and rotor get in, then finding tdc and going from there.