Hello, I have a 1995 Jeep xj 4.0 with a td04l 14t turbo running what my wastegate and boost guage said to be 14psi. I am using a msd btm to retard timing under boost and I just installed a split second aic1 a2h upstream injector controller. Before installing the aic I was using 2 36lb injectors run off of a 1psi switch. This system worked fairly well and I had no detonation and air fuel ratios were running 10-12. Than my turbo started smoking under boost so I promptly rebuilt it at installed an autometer boost guage. I took it out today and the turbo was much quieter and built boost more slowly and seemed to make less power. I was going up a hill in 3rd gear 4000 rpm 11afr 11psi and my engine started detonateing very bad. I let off the throttle and a huge cloud of smoke came out the exhaust and I had very little power but engine was quiet. I burned over a quart of oil on my 3 mile ride home so I am pretty sure my engine is blown. Why did my engine start detonateing now with just new bearings and rings in the same turbo. My afr was under 12 and btm was retarding timing 1degree per psi (14degrees total). My enginestarted blowing oil out the ccv valve on the valve cover (probably ring blowby) before it blew up meaning less compression than before therefore decreasing the chance of detonation. Oil in not milky, pressure line still hooked to msd waste gate never even opened because I never hit 14 psi. I am very confused on what happened and any help is appreciated so that I don’t kill my new engine when I rebuild it. Thank you.

 

Honestly it sounds like you had too many band aids holding it all together and one finally came off and had a domino effect. The cure would be a stand alone engine management system. Properly control injection and ignition plus be able to set up controls for your water/meth injection too.

 

Your gonna have to pull the head and see most likely but before that do a compression check. The btm could have failed intermittently enough to detonate possibly I’m not sure. If your afr never went lean. Captain Hindsight says: You should have invested in a aftermarket ecu with fuel and timing control lol.

 

Thank you for the responses. The engine was low miles (only 223000) lol. So I didn’t know how much longer it would live and 14 psi is a lot. Is it possible that ring blow by caused the detonation? I was experimenting with the msd btm timing retard and the dial was changing the timing so I don’t think the msd is the problem. I will check compression tonight and will probably have very little.

 

You can also try a leakdown test after the compression test that way you can figure out how the engine failed before tear down. Through the intake, cooling system, exhaust, crankcase. It’s gotta come out somewhere.

 

Possible the engine was hurt before the rebuild, and that's what was smoking. Also possible your rebuild didn't go as planned and your pouring oil from the turbo into the exhaust.

 

It's possible that on the extended pull the ring gaps closed up and broke a piston.

 

Before you start pulling the engine apart, check the compressor discharge area for oil. It is possible the compressor seal has failed - lots of oil in the intake will also give the symptoms you have.

 

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Thank you for the responses. I did a compression test and all cylinders had 150psi. 5 of My spark plugs were newish plugs and looked normal except for one that was missing the porcalin and was bent. I don’t know what happened to this plug but im glad it didn’t get stuck in my valve. Could this piece in my cylinder have been my detonateing like sound?The engine is quiet and revs fine with a new spark plug but can kill all the mosquitoes in a 3mile radius of where it is idling with oil smoke. At idle my valve cover ccv vent is smoking and blowing oil which baffles me because usually something with bad rings will do this but I have good compression. Coolant bottle is full and not bubbling and oil looks good. I checked for shaft play on my turbo and there was none. I will pull my dump pipe off and check for oil around the turbine. I didn’t expect my engine to have compression so I am even more confused on what went wrong. I am going to plug my turbo feed line and let it idle for a while and see if it stops smoking. Thank you again for the responses.

 

were you running at least one heat range colder than stock on those plugs? It could be the cause if someone dropped a plug on the floor or effect of that cylinder getting hot and detonating. Try a leakdown test too . At least you have a direction finding that cylinder.

 

so what are the findings on what failed in the engine?

 

I tore the engine down and my pistons had a lot of slop in the cylinder and 2 piston skirts were broken. No sign of detonating. The sound I was hearing must have been piston slap. so now I’ll have a new engine that can handle the boost. Thank you

 

Piston skirts often break due to rings not having enough end gap. Makes sense, as you were in a high load situation when this happened.

 

I hadn't ever heard this before, I thought it was usually the top of the piston that suffered the damage. I associate broken skirts with excessive clearance on a fragile piston.

 

There is a good chance I am confused and wrong as hell. I was envisioning the top of the skirt coming off above or below the top ring land which would not be the skirt at all. Doesn't make sense to break a skirt from ring deformation.

 

4.0's were terrible on piston skirts in stock form. It was typical to have a noisy one and find one or more in the pan.

 

Might wanna throw head studs on it while you're on there.

Another 4.0 jeep guy i follow on IG said he blew head gaskets at 10psi without cosmetics and studs.

 

You never mentioned a pressure test

#1 on the "Most common failure" list for turbo setups is people failing to perform a high pressure test (15psi+ or whatever boost you run) from the compressor inlet through the intake manifold.

Guarantee if you did NOT perform this critical test, you will find more than a couple leaks and potentially the cause of your failure and future failures if you don't fix the leaks.

Any leak no matter how small is air molecules leaking out which must be replaced by the turbine since the turbine is what determines how many volume/time the compressor wheel can move. So each intake side leak is additional backpressure on the turbine which raises EGT causing piston failure in any high temperature dramatic theatrical affect