454xl backfire through exhaust

It's been awhile since I've posted because everything has been operating as designed!
1995 Crusader 454XL with Quadrajet. Carburetor was rebuilt by Cliffs high performance 2 years ago.
Labor Day weekend went to island and everything ran fine. time to go home and port engine will turn over but not fire. I thought it was fuel pump again, so I pour gas in carb, still no start. got home on one engine and try starting fluid, still no start. Check for spark, no spark. Distributor pick up coil was bad. I couldn't get coil off distributor so i bought new distributor. put it in and we had spark!!!! KA BOOM.
Back fire out exhaust so bad, it blew muffler apart! No injuries and no boat damage. got muffler repaired by fiberglass guy.

Now the question: The engine starts fine and idles. All the gauges are reading correct values. Get underway and above 1500 RPM , engine backfires out the exhaust. pop pop pop

Compression test reads 150psi in all cylinders except #3 and #5. there're at 125psi.
No water in oil, and coolant expansion tank appears to stay at correct level.

What am I looking at? Head gasket? exhaust valve? ect....????

did you use a new cap or the old cap (and rotor)? if new, are they high grade marine parts (brass contacts vs aluminum)?

I'd recheck the high tension leads to ensure they are connected correctly.

If that checks out, I'd do a leakdown test... could be an exhaust valve has lost its seat...sometimes a miss at low RPM is hard to detect on a BBC...

After I replaced the distributer, and got the muffler back in, I replaced the cap, rotor, plugs, wires, oil and filter. Leak down test is next.

and maybe there is a miss at low rpm, like you said, just cant hear it

FWIW, I found it best to do any 'miss testing' with the engine under load, at idle, especially with the big blocks...

I'm assuming you re-timed when you installed the new distributor? I had a similar issue, not as bad as you, where there was popping when I installed a pertronix conversion kit. Long story there was that it wasn't compatible but i got rid of the popping by adjusting the timing. Maybe your base is off and throwing your advance off. Not saying it's pre-detonation but worth looking at to ensure timing is set correctly.

Yes, timing was reset after new distributor was installed. Did another compression with a GOOD gauge, 115 in all except #3, 90psi.
attempted to do leak down test. having a issue finding TDC on compression cycle. when doing leak down test, I hear air escaping from carb, and hoses from valve cover to flame arrester. I'm going to attempt another round of leak down test Monday.

If I removed the valve cover, would it be easier to get TDC?? when both valves are closed, TDC right?
I'm trying to determine if I have upper end problem or lower end problem.
If it is a upper end issue, no big deal to remove head and get it fixed. If its lower end issue, big deal, have to haul boat, get crane, ect.......

I would tell you to look at the plug wires sequence again. I can't tell you how many times I thought I had them on correctly and then found out I had a couple misplaced. Always feel stupid afterwards. Make sure number one is on the actual number one ha ha ha.

If I removed the valve cover, would it be easier to get TDC?? when both valves are closed, TDC right?

Click to expand...

Ayuh,..... That's correct,.....

plug wire placement was doubled checked before I moved to the next stage of troubleshooting. (I've got plug wires crossed many times) Right now I'm thinking it is a valve issue. I will attempt to do one more round of leak down testing. If I'm not convinced that the numbers are good, the valve covers will come off. Of course that is not as easy as it sounds. Coolant hoses, elbows, ECM's, ect... must be removed first.
Thanks for all the input so far. I'll keep my progress posted.

ok, so, I did a leak down test (3 times) and all the numbers appeared to be within range. 15-18% leakage. I took all plug wires off, Ohmed them and found one bad wire. I removed the new distributor and manually turned over engine to #1 TDC and reinstalled distributor so rotor is pointing to #1, reinstalled plugs, wires, and cap.
engine stared right up. once it got to temperature, i put it in gear. I heard no misses or backfire out the exhaust. Will sea trial next week and report back.
Happy Thanksgiving to all.

Excellent...hopefully, the report will verify you are back to 100%.

FWIW, I have seen many high tension lead failures over the years...the fastest way to identifying them has been to pop them off and do a modified wiggle test. with the 'gator clips' on the ohm meter leads in each hand, subject the wire to some modest flexing or shaking...any resistance change means its time to change ALL of them...some brands will last for years where others have seen issues after 200 hours...

ok. I went for sea trials today. Port engine started up with all the gauges reading normal. Its about a mile before I can get up on plane. After no wake zone, I slowly increased throttle. Noticed white smoke from port exhaust. At 2000 rpm;s the white smoke was bellowing out. Slowed to a idle and got back to dock. All gauges was normal. I checked the dip stick and it looked normal. Removed the oil fill cap and moisture but no 'milkshake'.

Ideas???

How hard is it to remove the heads? Any special tools??

white smoke is usually due to the coolant making it into the combustion chambers...could you smell any 'sweetness' in the exhaust?

Pulling the top end apart is pretty straightforward...biggest thing is to drain down the coolant ... may be worth checking your suspect cylinders' plugs......and spraying some WD-40 in to minimize any residue...

I did not smell any sweetness or coolant from exhaust. I will get exhaust hoses, elbows, and manifolds off in the next few days. Then the intake manifold. once I get the valve covers off, I'm going in blind.
Being in the marine business for 20+years, I know how to use my tools, but we were in the electrical/electronics/accessories side of the house, not the engine side.
I will keep ya'll updated as this project progresses.
Thanks for the input so far. Don't give up on me! I am sure there will be a bunch of questions from me as I dive into this.

Pretty sure you will find out it is a GenV block....with the MSTS controller on the EST distributor.

take plenty of pictures with the cell phone...and zip lock bags make excellent devices to keep things together.

The problem with your current situation is that your troubleshooting and diagnosis have not actually diagnosed the problem. And your original posted problem (after repairing the ignition system) of fuel in the exhaust causing backfiring has now morphed into an apparent coolant leak...and and a big one, not a drip, drip, drip. If you pull the heads the cause for all this may may be apparent, it may not.

Some things you might consider before pulling the heads would include a pressure test of your coolant system to confirm you have a leak. And purchasing a borescope attachment for your cell phone ($50-$90) to let you pull your plugs and inspect inside the cylinders for coolant. Or do what I used do and hang paper towels in front of the plug hole and rapidly turn the engine over and see what sprays out. But even if you find one cylinder sprays some coolant the leak could actually be in the exhaust manifold. A crack there will drip down onto an exhaust valve and fall into the cylinder when the valve opens. Given the exhaust explosion that destroyed your muffler that might be a better suspect than a crack inside the combustion chamber, which by design is pretty sturdy. If you find coolant you could then loosen the exhaust manifold and using some headless bolts pull it away from the block, then pressurize the coolant system and see where the leak really comes from. Of course I am assuming that it is not already dripping into the bilge. I don't know what sounds a cracked exhaust manifold might make but I suppose it could sound a lot like backfiring so keep that in mind.

As for the backfiring previously noted, if it returns and really is backfiring then you have ignition issues or valve train issues. The latter will show up in compression testing or leak down testing. I would do them carefully again and this time also test the starboard engine (known good engine) and look for differences. Ignition wise, I noted that after changing distributers, wires and plugs you later tested and found a bad wire. I find that concerning and if true makes one wonder what else might be wrong.

Good luck. If you do pull the engine apart be sure to follow Mark's advice and take lots of pictures and use the zip lock bags. It is useful to know which engine side has the problem before you go in, but with older engines it is always wise to "do" both sides (valves job and machine for flatness) as the undone one always fails three months later.

CaboJohn

It is the Gen V with MSTS ignition.
Cabojohn, I agree with you 100%. The compression and leak down test I did was not conclusive. I took the manifold (1,3,5,7side) off yesterday and no coolant came out of the exhaust part. I will get the other exhaust manifold off today and the intake manifold.
I have a box of zip lock bags and a box of tags with wire and marking all hoses and parts.
This engine was rebuilt 5 years ago because of faulty elbow. Exhaust manifolds were replaced also. so far everything has come apart easily with no broken bolts or knuckles.

I'm down to the head removal. got the other manifold off and water did leak out. So, now is it a head gasket (compression test was 115 in all except 95 in #3) or did the exhaust manifolds take the brunt of the explosion and did crack???
I'm thinking take heads off, and see if a 'smoking gun' head gasket is present.
I'd hate to have to get new exhaust manifolds, but.....
CaboJohn, I did not do a coolant pressure test because i haven't found one that fits on the filler neck.
Is there a way to test exhaust manifolds without a machine shop or any fancy tools?

was it water or coolant that came out of the second exhaust manifold?

as far as testing the exhaust manifold, assuming you have the center riser style, you'll have to make a blockoff plate for the elbow connection...you could use the blockoff plate and gasket but it may need some reinforcement. replace the hose barbs with pipe plugs but for one...that one should get a reducer/adapter to tie in a pressure gauge and connect your compressed air source. 20 PSI should be adequate.

as far as testing the cooling system, they make adapters for 'normal' cooling pressure testers...I can't tell you which one as I've never had to test one of those...I've heard there are a few out there that require custom test adapters...

If it has the same HX as the markIV BBCs (the model 350 (454 CID)), the 'normal' adapter works fine...and its a 7lbs system, going off memory...

I've done it, but I am not a big fan taking off heads unless the issue is diagnosed in advance. One often finds that all "looks" good once they are off and it becomes difficult to do further diagnostic tests because everything is in pieces.

Usually you know you have a coolant leak because coolant is missing in normal operation and the question is "where is it coming from and/or where is it going"? I have not worked with your engine but on mine I have done a pressure test on the coolant system by pulling a temp sensor from the manifold and attaching a pressure gauge, or by attaching a "T" so I can have a gauge as well as a schrader valve to put in air. I have also used a GM coolant additive that glows in UV light and then gone to the boat and ran it in the dark. I did find the slow drip leak but unfortunately the additive (approved for Dexcool) turned the Dexcool bright green so it look like ordinary coolant. Probably confusing to the new owners.

I have tested the exhaust manifold for coolant leaks by blocking off the elbow connection (as Mark suggests) and then pressurizing the coolant passageway with air while filing or submerging the manifold in soapy water. Lots of bubbles if you have a leak!

The water or coolant question Mark asks is a good one. Coolant makes a colored stain on a paper towel and that tells you that you have found a problem that needs fixing. If it is water, then it comes from the elbow and was either a bad gasket installation (which you will fix on reassembly) or more like is due to lack of care when taking off the elbow. It must be drained though the plugs in it's side and them very carefully, levelly and slowly removed so that you don't dump salt water into the exhaust manifold. This is not good for the engine but in any case, regardless of the source of the water, this is not the cause of any of your issues that you have noted.

I've never heard of a exhaust manifold or elbow failing because of a backfire. I will attempt to pressure test the manifolds before head removal. I'm still leaning on head gasket failure.
With the oil being milky, should i drain it and some how flush the crank case?
thanks again guys for the input. Wish ya'll was my beer drinking buddys next door!!

In post #12 your oil looked fine ("no milkshake"). In post #21 you are asking should you drain out milky oil. Situation and likely causes are rapidly becoming more serious. Anything that could get coolant into the exhaust (white smoke) and also into the oil (milkshake) must be pretty bad. I could speculate but let us know what you find when you pull the heads.

CaboJohn

Just dropped heads off at machine shop. No visible damage. Cylinders look fine. No water or coolant on pistons.
Before I tore it down, I checked dip stick and no water or fouled oil. I notice the milkshake after I pulled valve covers.
NOW,,,, I Checked the exhaust manifolds. Test 1: Blocked off the lower fitting that carries coolant back to HE. Poured acetone in top coolant fitting. Filed it up until the acetone was level with the elbow flange. No acetone ran out of the exhaust ports.
Test 2: Made a plate to fit the elbow flange with 3/8 aluminum and new gasket to block off elbow flange. I plugged the lower coolant fitting and rigged a fitting for the upper coolant inlet with a Schrader valve. I layed the manifold on its side and filled with water through the exhaust ports, then pumped 20psi into it. I have bubbles coming from # 8 exhaust port and # 5 exhaust port. They are companion cylinders I think.
CaboJohn, you might have hit it with blown exhaust manifolds.
The heads should be done by end of week.
Will update

Wow!...I'd say you have a plausible explanation for the white smoke in the exhaust.

You said earlier that the engine in question had new exhaust manifolds and riser done a while back...do you know who made the parts that were used?

sounds like with some cleanup and a gasket set, you should be running before Xmas...

That's promising but you want be sure that you are not getting a leak from your block off gasket on the elbow flange that is creating confusing bubbles. I would fill a bucket with soapy water, pressurize the coolant passageways on the manifold and then stick various parts of the manifold into the bucket until you see a clear stream of soap bubbles coming from the exact spot of the leak.

Good luck.

Cabojohn

The exhaust manifolds were installed 5yr ago. The elbows last spring. I get them from Macomb marine. The exhaust manifolds have the Crusader flag on them. I went the cheap way when I first got the boat. Lesson learned!!!!
I will retest the manifolds again as CaboJohn suggested.
thanks again for all the help! Boating by Christmas would be a great gift to both of us.

When asking about the source for parts, was more interested in the manifold (with the issues)...I've seen a few GLM castings with issues and read about many more (but can't say I've seen anything on a failure like you have described)...

Agree with John's thoughts on verification but, based on the description, I'm thinking the leak in 'inside' the exhaust passage(s) and may not be visible without a borescope (or similar camera)...

Heads are still at machine shop. He still hasn't looked at them. Next week.
I retested exhaust manifolds as CaboJohn recommended. Filled up large storage tub with water and dunked manifolds in and pumped 20psi in coolant passages. Same results. I have big gulping bubbles out of the exhaust port (#8 & 5). I will order new manifolds after I get the heads back.
What about the exhaust elbows?? Should I get new ones??

If they are two years old, you probably still have a few more years left on them...your location indicates salt water so I'd expect 5-7 years service life at the most.

I'd check the mounting flange for leak indicators and flatness..if they are ok, you should be ok...

Still waiting for heads.