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... and the backfiring continues...

A couple of things stood out for me on your recent posts. What carbs are you running? In your first post you reported 6 psi fuel pressure, in your recent post you report 8 psi, that seems a little high to me but may be acceptable for your carb. Check carb spec. Also, re your timing readings, do you have 8 deg base timing? And do you have an advance curve you could reffer to?
 
fastjeff said:
..."I replied to your post already.."

Sorry--I missed that.

How "weak" are those two cylinders?

Jeff
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How weak WERE they... barely a noticeable rpm drop by ear. Again, after re-adjusting the valves, all cylinders get the same audible rpm drop. I did not have a shop tach to see actual rpm drop, but they all feel and sound equal now.
 
WoodieMan said:
A couple of things stood out for me on your recent posts. What carbs are you running? In your first post you reported 6 psi fuel pressure, in your recent post you report 8 psi, that seems a little high to me but may be acceptable for your carb. Check carb spec. Also, re your timing readings, do you have 8 deg base timing? And do you have an advance curve you could reffer to?
Click to expand...

Quadrajet. The first time I checked fuel pressure was months ago. Probably remembered wrong. timing with advance disabled is set to 12 degrees at idle, and max advance is 30 degrees at around 2500 rpm (obviously.advance not disabled). I do not have a "curve" to follow, but it advances with rpm up to 30 max.
 
Agree 8psi is on the upper end of acceptable. As long as you don't see the pressure rise with rpm and don't see any extra fuel overflowing, it's probably ok, as is.

Assuming the worst case cracked block scenario isn't the issue (you guys don't see 'freezing over there, do you?), did you ever run the engine up to 'backfire speed' with the timing light on? Looking for an indicator its spark, not fuel. Up to 3000 rpm should keep the spark rate of the coil in a range you eye can detect any changes (drop outs).

When you did the "Jumper to the coil", did you leave the harness wiring connected?

I'm going down the path that says things were well a while back, bolt ons behave when swapped to other engine....what's left??? The stuff you haven't swapped yet and the harness is one item. I think you mentioned no more connector in the harness...maybe a strand out of a connector or some abraded insulation? for a couple minutes, its another easy check and covers an unchecked item.

Had a "loss of power" issue one time on our port engine. After the gear was removed for unplanned service. Got it fixed and ran around to the ocean. Next trip out, 5 miles out of the inlet, the engine bogs and studders and then runs fine for another two minutes. When it happened again, slowed down and popped the engine cover. idled fine....nothing obvious. Back up on plane and 15 minutes later, the issue recurs. long story short - the guys that overhauled the gear put the pump housing in upside down - they had to slide the gear back (after launch) and spin the pump housing. In the interim, one of them 'loaded' the HX hose/fitting and cracked it - right next to the NO STEP sticker. The coolant was squirting onto the hi tension wire and killing the spark. Idle down, pressure drops and squirt stopped....found thru constant observation.
 
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May not be the issue here but i'm sure 8psi is too high for a quad unless we're accounting for the gauge's accuracy. Not completely familiar with this app but shouldn't it be 8 deg base timing for a 454?
 
Pretty sure Crusader has used 10 deg BTDC for initial timing for these since they made them...Personally, we set the distributor at max advance and let the initial fall where it will. You have no other choice with an electronic (advance) system. On the rare occasion where a hot restart issue develops, you may have to back it off a few degrees. A full mechanical setup will let you adjust both ends of the timing curve as necessary.

I think Eric has ID'd a key point with his issue - the engine won't rev up in neutral w/o the backfire. With his carb setup, he's seeing an issue with the carb functioning on only the primary circuit and this carb works acceptably on the other engine. Assuming the fuel pressure doesn't increase with rpm (blowing the needle off the seat), I'd bet the ignition is the culprit. Being as he's swapped the coils and the complete distributor, that only leaves the wiring. my two cents.
 
I had the same backfire problem on a OMC - V8 a few years back . Engine came into my shop, we pulled the heads sent them out for R&R came back still hand the problem. we pulled the heads back off, this time I took them back to the head-shop. The machinist said the heads were fine. I said show me the valve spring pressure. Marine valve springs have a higher
spec. than auto - "His it's OK" was 75 lbs, book spec. was 85lbs min ! we replaced and shimed to the right spec and
wala---- 4500 rpm . Be sure your head-shop understands "marine" heads.

Never approach anything faster than your willing to hit it".<
 
Okay, got a fresh set of eyes down there Wednesday night, but had to call it early because I sliced my hand open and had to hit the emergency room. Never a good thing when you can see your own bones, LOL.

So, last time I was pulling plug wires and listening for RPM drop, I wasn't paying attention to something I apparently SHOULD have been paying attention to ("Thanks Captain Hindsight!").

My buddy started from square-one and began checking everything I have already checked. When he got to pulling plug wires at the distributor, he looked a little puzzled and asked me to fire up the other engine. I did, and he pulled a wire off the good engine's distributor. Same RPM drop as what the problem engine gets, but ZAP! ZAP! ZAP!... a two-inch arc from the cap to the wire. Back to the problem engine, and it will only arc about a quarter-inch. The wire has to practically be touching the post to get any arc at all. WEAK SPARK!!! WOOHOO!!! We've found the problem, now we just need to find the cause. This is right about where a band clamp got the best of me and we bailed for the night.

Sooooo..... I know it is not a voltage issue as we jumped straight from the battery to the coil. I know it is not the coil, plug wires, plugs, distributor... Ground issue?? My brother went down last night and ran a new ought-gauge wire from the battery negative to the bellhousing. No change.

I have been trying to read some stuff online, and one random suggestion I found was that a bad tach could cause a weak spark. Seems kinda odd, but anything is worth a shot at this point, and pretty easy to check. Not sure if I will make it to the boat today, but I am going to cut the entire harness and run the engine off a "box" to see if we get a better spark and rev beyond 2800 RPM. We had an issue with that tach when we first bought the boat, but were able to re-calibrate it from the back-side of the gauge. Maybe... just maybe this could be the problem?

Sorry for being so verbose. My fingers get moving and have a hard time stopping, hehe.
 
200toncapt said:
I had the same backfire problem on a OMC - V8 a few years back . Engine came into my shop, we pulled the heads sent them out for R&R came back still hand the problem. we pulled the heads back off, this time I took them back to the head-shop. The machinist said the heads were fine. I said show me the valve spring pressure. Marine valve springs have a higher
spec. than auto - "His it's OK" was 75 lbs, book spec. was 85lbs min ! we replaced and shimed to the right spec and
wala---- 4500 rpm . Be sure your head-shop understands "marine" heads.

Never approach anything faster than your willing to hit it".<
Click to expand...

Thank you for the suggestion, but his first question was, "marine or auto?" He checked everything as a marine application, and I trust the shop. I have dealt with them for a decade or more now.
 
makomark said:
I'd bet the ignition is the culprit. Being as he's swapped the coils and the complete distributor, that only leaves the wiring. my two cents.
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Ding-ding-ding!!! We still need to locate the CAUSE of the issue, but we have a winner! Definitely a wiring/electrical issue. You have PayPal Mark? PM your address and I'll send you a case of beer in the brand of your choice (ie. $30). It's the least I can do; especially given the time you spent sending me that manual.
 
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WOOHOO!!!!! Got it!!! Phucking tachometer this whole time. Cut the tach signal wire right at the gauge and the motor revs to the moon now. Good strong arc when I pull a plug wire... Problem solved! Thank you all for the replies, and Mark... I owe ya buddy!

Now let's go fishing!!!
 
wow, so a bad tach was the root cause? This is one of the posts you file away in the back of your mind and never forget.

thanks for posting all the details.... I know it was a painful process, we've all been there.

Bob
 
Pull the coil wire from the distributor and see how strong the spark jumps to ground as the engine is cranked. If you have a strong spark from the coil wire but not at the plug wires, check for a problem with the cap or the rotor. Keep both hands away from sharp objects....that red stuff leaves a nasty stain!
 
bobct said:
wow, so a bad tach was the root cause? This is one of the posts you file away in the back of your mind and never forget.

thanks for posting all the details.... I know it was a painful process, we've all been there.

Bob
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Yeah, can you believe it??? I don't really understand it, but I don't care... IT'S FIXED!!! LOL
 
bobbyc said:
Pull the coil wire from the distributor and see how strong the spark jumps to ground as the engine is cranked. If you have a strong spark from the coil wire but not at the plug wires, check for a problem with the cap or the rotor. Keep both hands away from sharp objects....that red stuff leaves a nasty stain!
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Not to be rude, but have you read the entire thread? I know it's long, but I have been there, swapped that. Cap and rotor are fine. Problem was found and solved. Bad tachometer.
 
Oh my God, this is the most incredible thread on this site! All that time and labor for a freaking bad tach?!!! I'm glad its fixed Eric but I feel for you buddy.
 
LOL, thank you sammi. Yeah, this was a nightmare, but I am glad it is gone. The worst thing about it, I am an ASE and Honda Master Technician. Everything I could possibly think to check, and I could not find the problem. All the while I have been thinking, "some tech I am." Now I don't feel so bad, LOL. Who would have thought a gauge would cause a backfire?
 
Glad you found the cause and resolved it....you don't owe me anything though tokens of appreciation are welcome.

I've seen a few bad tachs over the years and they usually come in two flavors. the output circuitry goes on the fritz and the pointer becomes erratic/inaccurate or the input circuitry fails and the ignition won't fire at all. this one is a first for me.

Also, remember the technique your buddy reacquainted you with - use the "twin" as a point of reference. As many here will attest, that trick will come in handy in the future.
 
I can attest..... That TWIN thing helped me on a few occasions. Heres a few tokens to those who have helped me over the years...JUST IN CASE I may have let one slip ! You guys all know who you are. In the last two seasons, we have had decent performance from the boat. Of course, now that I have said that.......
 
The tach no way. Someone has to look in this guy's marina junk pile for the new engine shipping crates :) That's how he fixed it
 
I seriously doubt if a cracked block will cause backfiring!

I suspect you have an exhaust valve hanging up on you--especially with that engine (which is famous for sucking in water through the exhaust ports). How to test? Remove the valve covers and whack each exhaust valve with a hammer. The valve should open with the hit then snap right back shut. If not, you can remove the valve springs (with a tool and air holding the valve closed). You can then throw away the factory seals (a mistake in every case) and hit the stems with some penetrating oil.

Jeff
 
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