Backfire thru Intake after warm, 2600-3600 RPM

[Trucky]

99 210SD 5.0 MCM 2 barrel with 350 hours. Only after it warms up does it begin to backfire through the intake under load. It only seems to happen between 2600-3600 RPM. Above 3600 on up to WOT at 4800 seems to run fine, as well as lower RPMs and idle speed. It has a fresh tank of non-ethanol regular, properly laced with Startron. New plugs last summer. I'm not sure on the age or condition of the rest of the ignition system or the timing. Any thoughts on where to look?

 

[Lazy Daze]

Boy, that sounds exactly like the problem I had a few years back. Although, I never pushed through the backfiring to see if it stopped at higher RPM's. Mine would not occur until I hit 3400. In my case it was just a bad ignition module (about $60, IIRC). It's located under the distributor cap. While you're there checking it out, take a look at your cap and rotor, too.

 

[Trucky]

I see an ignition module for $230 and an ignition sensor for $46. I wish this were new enough to be able to read codes and diagnose without tossing parts at it...

 

[CliffA]

just an idea to consider....if you happen to have an old set of spark plug wires you may want to install them and see if that helps...i had a plug wire go bad once on one of my cars that acted a lot like you are describing....

cliff

 

[Lazy Daze]

I see an ignition module for $230 and an ignition sensor for $46. I wish this were new enough to be able to read codes and diagnose without tossing parts at it...

$46 sounds in the ball park, although on the cheap side. It's definitely NOT $230. It's right under the dist cap.

 

[Trucky]

just an idea to consider....if you happen to have an old set of spark plug wires you may want to install them and see if that helps...i had a plug wire go bad once on one of my cars that acted a lot like you are describing....
cliff

No spare wires here but not knowing when they were last changed I'm thinking that should be on the list too.

$46 sounds in the ball park, although on the cheap side. It's definitely NOT $230. It's right under the dist cap.

I found this one... Is there any way to determine if this component is bad without an ECU on board or special equipment?

Distributor Sensor

SKU: 892150K02
Length: 3.875 inches
Width: 2.875 inches
Height: 4 inches
· Price : $71.25

Fits GM V-6 & V-8 engines w/ Thunderbolt IV & V ignition

View attachment 25415

 

[Lazy Daze]

That's it. No, there is no way to use a scanner to tell if it's bad - even if you did have fuel injection and an ECU. I'm not sure if there is any other way, other than swapping it out and trying it.

 

[kbsunlovers]

Good prices - mind sharing where you found them?

 

[Trucky]

I'll tread carefully here... That's actually not the best price by several percent. You could Google the SKU and likely see several players for that particular part. There was one website where I could input my engine serial number and get blowup drawings and part numbers for virtually every Mercruiser component. If you don't have the part in hand and able to physically compare them, this might be the most accurate path.

 

[Quint4]

I just paid $64 each for two ignition sensors. That is the new style with the ground lead (attach it to the ground stud on the block).
They are a superior design to the old style. Merc has a bulletin out on replacing the old style with the new for a no start condition and poor performance. Replace it now.

 

[Lazy Daze]

I just paid $64 each for two ignition sensors. That is the new style with the ground lead (attach it to the ground stud on the block).
They are a superior design to the old style. Merc has a bulletin out on replacing the old style with the new for a no start condition and poor performance. Replace it now.

Thank you! I knew there was something else I wanted to say, but forgot... Pull it out and take a look at it where it mounts. Make sure everything looks clean and reinstall with a SMALL amount of dielectric grease. See what happens.

 

[edsmax]

Im confused - according to Mercury parts express, it says my original part # for this (2002 EFI engine) is 861780A2 and that it has been superceeded by 892150A02. When I do a search for the new number, I get 892150Q02 as another replacement - the AM Sierra version is here:

http://www.marineengine.com/newparts/part_details.php?pnum=SIE18-5116-1&ptype=&Engine=&Model=

Is this the newer design??

 

[Trucky]

Thank you! I knew there was something else I wanted to say, but forgot... Pull it out and take a look at it where it mounts. Make sure everything looks clean and reinstall with a SMALL amount of dielectric grease. See what happens.

Forgive my ignorance... where does the dielectric grease go? If I were to guess I would say at the electrical connectors, but I've been known to guess wrong.

So far I have suggestions to:

1. Replace the ignition sensor - new style with ground lead, use some grease somewhere.
2. Maybe replace spark plug wires

I know I should look at the cap and rotor for corrosion or damage and replace if needed.
Is this something that could also be caused by a bad or failing coil?

 

[CliffA]

Forgive my ignorance... where does the dielectric grease go? If I were to guess I would say at the electrical connectors, but I've been known to guess wrong.

So far I have suggestions to:

1. Replace the ignition sensor - new style with ground lead, use some grease somewhere.
2. Maybe replace spark plug wires

I know I should look at the cap and rotor for corrosion or damage and replace if needed.
Is this something that could also be caused by a bad or failing coil?

dielectric grease is non-conductive grease that is used on electrical connections to seal out moisture to prevent corrosion....after the electrical components are connected while 'dry' you would apply the dielectric grease to the connection as protection.....do not apply the grease to the components before they are connected, only after....

cliff

 

[Trucky]

So, still working through the "possibles". So far we've replaced the distributor cap, rotor and ignition sensor, all which had visible corrosion on them. Found the ignition timing to be several degrees advanced and with a loose set screw. The engine runs much much better now but I still get a rare backfire. I ran about 30 minutes at 3200 rpm before we felt and heard the first backfire. I can make it happen most times by going WOT where it will plane off, backfire and act like it dies for a second or two. Then it picks right up and runs fine. I've had two fillups with Startron dosed so I hope I can assume the gas is good.

The mechanic working on it for me says it could still be the coil and has one on order. Said if that doesn't fix it then the coil will be a freebie. He also thought it could possibly be a burnt valve hanging up occassionally.

All those parts so far really needed to be replaced just visually so I'm ok with the process of starting with the least expensive potential cause. So, after the coil, if the problemn still exists would plug wires be a likely cause still? Seems after that the ignition system would be mostly new...

Time to get out on the lake before the nutjobs wake up.

As always, I appreciate and value all thoughts and opinions. I feel miles less ignorant dealing locally when I have the corporate knowledge and support of CSR!