5.7L Spark and Fuel, But Wont Hit?

sjohnson44

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Just got a newly rebuilt merc 5.7L with Thunderbolt V installed and trying to get it cranked.
Going by the troubleshooting flow chart, it asks if I have 12V at Coil +, when I checked it I have voltage but its 9V at coil +.

Also have 9V at the white-red wire from ignition module.
I am unable to check the white-green wire as I do not have a spark gap tester.

Battery has full charge on it.

I am getting spark to the plugs.

The flow chart suggests either the ignition sensor in distributor cap, or the ignition module. But without having a full 12V at either one I can't say if either is bad.

Anyone have any suggestions?
 

Bt Doctur

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19,093
Re: 5.7L Spark and Fuel, But Wont Hit?

Who assembled it? If you ,check firing order with #1 on compression stroke TDC.
spark, fuel, compression and it should lite
 

Bondo

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Re: 5.7L Spark and Fuel, But Wont Hit?

Just got a newly rebuilt merc 5.7L with Thunderbolt V installed

Ayuh,.... What was the motor, 'n ignition before,..??
 

sjohnson44

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Re: 5.7L Spark and Fuel, But Wont Hit?

It was original motor in the boat, just a complete over haul.

I installed the distributor with the #1 piston on compression stroke and pointed the rotor at the #1 cylinder, then installed the cap with the rotor on the #1 spark wire.

I just went and bought a spark gap tester and turns out with the white green wire unhooked and tapped against ground the coil sparks. So that says that I need a new ignition sensor. I dont know guys, to me it seems that having spark at the coil is a good thing, so why would it be bad in this case?
 

Don S

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Re: 5.7L Spark and Fuel, But Wont Hit?

I installed the distributor with the #1 piston on compression stroke and pointed the rotor at the #1 cylinder, then installed the cap with the rotor on the #1 spark wire.

Did you have the timing marks on the cam and crank in alignment as shown in the manual ? Like this when you set your distributor?

attachment.php



If so, that is not #1 TDC on the compression stroke, that is on the exhaust stroke. That will also affect the lifter adjustment if you thought you was on the compression stroke. You will have to do that over as well, because you probably don't have compression on a couple of cylinders.
 

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sjohnson44

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Re: 5.7L Spark and Fuel, But Wont Hit?

I didnt install the cam. I had a engine shop do the over hauling, all I had to do was install heads and intake. So I am unsure of how the timing chain gear was installed.

So would I need to take distributor out and find #1 TDC again? It is when the #1 piston is at the top of its stroke correct? Or when it just starts to come up?

I installed the distributor when I first felt air come out of the cylinder.
 

Don S

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Re: 5.7L Spark and Fuel, But Wont Hit?

I installed the distributor when I first felt air come out of the cylinder.

That in itself is a long way from TDC. As soon as the piston starts moving from the bottom of it's stroke, you will feel air coming out. You still have just under a half a revolution of the crankshaft to get to TDC.

Read this, http://forums.iboats.com/showthread.php?t=427081

If the rebuilder adjusted the valves, which I would assume he did, they are probably fine.
 

Scott Danforth

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Re: 5.7L Spark and Fuel, But Wont Hit?

make sure the timing mark is on TDC as well. just letting your finger start to push off is not enough. then make sure your distributor is lined up with #1 cylinder. this will get you close enought to get it to fire.

because you have only 9 volts, you also have an electrical contact issue somewhere. start by cleaning all your contacts.
 

sjohnson44

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Re: 5.7L Spark and Fuel, But Wont Hit?

Thanks for the link Don, I will double check that in the morn.

Scott, the battery also read ~9V when cranking the motor. I put it back on the charger to be sure that it is fully charged. Will also try again tommorrow.


But am I still going to need an ignition sensor even if the distributor is in wrong?
 

Scott Danforth

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Re: 5.7L Spark and Fuel, But Wont Hit?

if your distributor is in wrong, its like shooting to the north and expecting the bullet to go east. your rotor is not pointed at the right plug when the coil fires.
 

Don S

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Re: 5.7L Spark and Fuel, But Wont Hit?

But am I still going to need an ignition sensor even if the distributor is in wrong?

How do you know you need a new one? If you don't have the right voltage to the + terminal on the coil, the rest of the tests mean nothing.
 

sjohnson44

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Re: 5.7L Spark and Fuel, But Wont Hit?

Following the flow chart suggests I need a new one. But you are right, need to take this one step at a time.
I will double check battery and #1 TDC in the morn and report my findings.

Thank you for everyone's help. I sometimes get flustered and side tracked, just need a good smack in the head to get me goin straight. lol :)
 

boatguya1

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Re: 5.7L Spark and Fuel, But Wont Hit?

Following the flow chart suggests I need a new one. But you are right, need to take this one step at a time.
I will double check battery and #1 TDC in the morn and report my findings.

Thank you for everyone's help. I sometimes get flustered and side tracked, just need a good smack in the head to get me goin straight. lol :)

I don't have the chart in front of me, but I think you are missing a step prior to tapping the grn/wht wire. If you have spark you never get to that test. It assumes you have no spark due to the sensor in the dist being bad, It then simulates the sensor by tapping the green wire.

End result is if you have spark there is very little chance the sensor is bad. (not in that test, when cranking the engine)

James
 

Don S

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Re: 5.7L Spark and Fuel, But Wont Hit?

The chart isn't going to help you if the voltage to the coil is only 9 volts, that low voltage will prevent the ignition from working at all.
 

sjohnson44

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Re: 5.7L Spark and Fuel, But Wont Hit?

Ok, I got 12V at the coil now and I double checked my TDC. I cranked till I felt air coming out of #1 cylinder and then checked my mark on the balancer and rotated till I was at 0 degrees. I checked the rotor and it was actually on the #2 cylinder, I rotated it around and got it on #1.

Now after attempting to start the engine, it tries to hit but no cigar. Just backfires and sputters.
 

81 Checkmate

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Re: 5.7L Spark and Fuel, But Wont Hit?

It sounds like it is still out of time.

You said in an earler post that you installed the HEADS and INTAKE ! is this correct?

How did you adjust the rocker arms?
 

sjohnson44

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Re: 5.7L Spark and Fuel, But Wont Hit?

Yes I did.

I rotated the engine until the lifter was all the way down and tighten the rocker until I just couldnt turn the push rod. I did that for each lifter.

There is a tube coming out of the back of the carb, I tried plugging it off and it actually tried to run but it would start but rotate slowly like it was lugging down. It rotated like that probably 3 times around before quiting.
 

Desertsky

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Aug 25, 2010
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Re: 5.7L Spark and Fuel, But Wont Hit?

You should either take it to a reputable boat shop or take a class in engine tuning. Trying to diagnose and cure these problems on a forum is too hit or miss. Unless you KNOW where everything is set, you don't know if it is right.
 
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