1990 mercruiser 4.3 no spark

[trashboat]

Firing order is correct, set the base timing with cylinder 1 at TDC, distributor rotor pointing at cylinder 1, and lining up 0 degrees on the timing mark, and still not firing.

Checked several times and it all seems to be correct, I think the previous owner put a distributor in is it possible that it's in backwards?

 

[alldodge]

I think the previous owner put a distributor in is it possible that it's in backwards?

Not possible if you aligned TDC on No 1 and then made sure the distributor is pointing toward number 1

 

[ESGWheel]

Making sure the term ‘still not firing’ is understood:
* You still have spark at the plug and validated post setting the timing while the engine is being cranked (want to be sure something was not knocked off)
* the engine cranks (turns over) strong but does not catch aka run aka fire (strong is an indicator of good battery and even the noise of it cranking - if proper - is an indication of good compression)

If both above true than is there a history of engine that may lead to no or low compression?

Can u post a video of it being cranked ?

 

[trashboat]

Correct I have spark at the plugs, and the engine cranks strong and sounds as it should.

I don't believe it ever had any compression issues, but I was going to check compression next to be sure.

I can take a video of it tomorrow cranking, and it does seem like it wants to start it's sputtered and backfired.

I have it set up to pump fuel out of a small can just for diagnosing and its getting fuel in the carb.

The only other thing I have done is the tach wires are removed from the coil, and when trying to start it I have a jumper from the battery to the + on the coil.

 

[ESGWheel]

Cool

Also, and need to be careful with it, got any starter fluid?

You sound experienced so I suspect u know how to use it but if never have: squirt a second or so into carb before trying to start is my first step then I get progressively more aggressive if sputtering but not fully catching but only to a limit - easy to ruin an engine or start a fire

 

[trashboat]

Cool

Also, and need to be careful with it, got any starter fluid?

You sound experienced so I suspect u know how to use it but if never have: squirt a second or so into carb before trying to start is my first step then I get progressively more aggressive if sputtering but not fully catching but only to a limit - easy to ruin an engine or start a fire

Yeah I poured some fuel down the carb and gave it a little sniff of ether and it sputtered/backfired the same.

If compression is good, it's getting fuel and has spark I'm not sure what else could be the issue unless it's the distributor itself shorting out, but if that was the case I'm not sure I'd have spark at the plugs.

To me it seems like something is off with the timing, but I checked and double checked it with the same results.

Thanks for the input I will post a video tomorrow and check compression.

 

[ESGWheel]

U hit on the three basic ingredients
If good compression and u know it is getting fuel I’m going to lean as u are…

I’ve got a tool I’ll post that allows to see if getting spark while cranking - and not a spark gap one … not cheap and may take a week or more to get it, but I’ve got an idea I’ll PM u about…

 

[nola mike]

Not possible if you aligned TDC on No 1 and then made sure the distributor is pointing toward number 1

Possible if it's pointing at the position that #1 *should* be. Op, it should be pointing at the #1 plug wire, correct?

 

[trashboat]

Possible if it's pointing at the position that #1 *should* be. Op, it should be pointing at the #1 plug wire, correct?

Correct it's lined up with #1 spark plug wire on the cap, with cylinder 1 piston at TDC

 

[ESGWheel]

Here is the tool I was referring to (link). Seems like availability is now growing. Previously I had to get fm the UK but still about the same price (but I paid $ shipping). Here is a review fm the UK and too funny he mentions had to get his fm the US (link). The advantage is you clip it on the wire, go try and start the engine and it will record what you got for spark (strong or weak). You can use this from one plug wire to the next as well to test them all looking for a fouled plug or bad wire. I thought I did a post on this but may have been in another forum as I could not readily find it.

 

[nola mike]

Correct it's lined up with #1 spark plug wire on the cap, with cylinder 1 piston at TDC

Also are you sure you're on the compression stroke?

 

[alldodge]

Possible if it's pointing at the position that #1 *should* be. Op, it should be pointing at the #1 plug wire, correct?

We wordsmithing now

 

[nola mike]

We wordsmithing now

Maybe, but isn't always obvious to someone that the location of #1 can move and isn't necessarily where the diagram on the net says it is

 

[trashboat]

Cylinder 1 is TDC, rotor pointing at cylinder 1 plug wire and timing mark at 0 degrees. That would the compression stroke right?

 

[trashboat]

Cylinder 1 is TDC, rotor pointing at cylinder 1 plug wire and timing mark at 0 degrees. That would the compression stroke right?

 

[Chris1956]

Sure that is compression stroke half the time. The cylinders fire every 720* of rotation in a 4 cycle motor. You might pull the distributor, rotate the engine 360* and reinstall it pointing to #1 spark plug wire.

 

[nola mike]

Cylinder 1 is TDC, rotor pointing at cylinder 1 plug wire and timing mark at 0 degrees. That would the compression stroke right?

Only every other rotation in a 4 stroke.

 

[alldodge]

If your cranking and all it's doing is back firing, do pull the dizzy noting where it's point now. Doesn't matter where it's pointing only that you know where it is now.

Pull dizzy and rotate rotor so that it's 180* and reinstall. So it will be pointing the opposite direction it's pointing now

 

[trashboat]

If your cranking and all it's doing is back firing, do pull the dizzy noting where it's point now. Doesn't matter where it's pointing only that you know where it is now.

Pull dizzy and rotate rotor so that it's 180* and reinstall. So it will be pointing the opposite direction it's pointing now

Okay I did try this yesterday while I was messing around and it still didn't fire, can't remember if it stopped backfiring or not though.

 

[Scott06]

Okay I did try this yesterday while I was messing around and it still didn't fire, can't remember if it stopped backfiring or not though.

and you have checked the strength of spark with gap tester? basically confirm you are getting spark

Was intake recently off and there is possible vacuum leak or just chasing down the no start condition ?