Testing For Cracked Head

Well I got this from my sniper efi tuner…so I guess now I have to see if I have a cracked head. What is the best way to diagnose it? Compression test, other? I have never had missing coolant, frothy oil or white smoke. The Jeep is running like a top now with my 5th tune iteration, except for a surging idle that shows up. I do have the Hall effect sensor.

This is from tuner after persistent surging idle:

“Did you ever put any thought into my cracked head suggestion? Its very common on the older iron heads of this era, and its fits the symptoms to a tee... its very temperature dependent, and nothing ive been able to do with mixture, richer or leaner, affects it... and the vacuum signal while surging, it text book cracked head or valve seats... “

 

Your FLAPS may let you use an exhaust gas sniffer at the radiator fill inlet.

 

Failing the emissions sniffer, there are kits that look for exhaust gas in the coolant using chemicals. The sniffer would be free if available - that's likely what a shop would do.

Look here -

 

A cracked head will usually have symptoms with coolant. Coolant in the oil, or visa-versa. A leaking head gasket can have some of the same symptoms, as well as low compression in the offending cylinder.
I have a magnflux tester to check iron heads for cracks. I’ve seen lots of heads with cracks, usually in the combustion chamber with a crack between a valve seat or spark plug hole. The engines were running fine with no symptoms until a visual inspection at rebuild time. Those type cracks have no effect on the operation of the engine, but can have issues when installing new valve seats.
Aside from coolant symptoms, I can’t see how a minor crack, if any, would cause a surging idle. This seems to me to be a glitch with the fuel injection due to a vacuum leak or sensor with an out-of-range signal.
If the engine otherwise runs as well as you suggest, I doubt possible cracked heads are an issue.
-Donny

 

If it was an F-head I'd suspect worn throttle shaft bores, making an air leak.

 

Is this the tool along with a chemical, or is it something else? https://www.oreillyauto.com/detail/...s-evertough-combustion-leak-tester/ren1/67094

I am frustrated. I have sunk a ton of time and money in this sniper, but can’t shake this idle thing. I’m hoping the tuner isn’t throwing a red herring for me to chase but I don’t know anything about the engine so he may be right. One of the reasons I didn’t mind all the effort of adding an external fuel regulator is thatI can regulate back down to 5psi and put the carburetor back on once I have had enough is this experiment.

 

I have never looked into fuel injection, so have no first-hand experience. I know some other members have gone this route, and remember lots of issues when applied to the odd-fire Buick V6. Many aftermarket setups couldn’t run properly when using the distributor for the trigger devise. I think some of the problems were overcome by mounting an external trigger off the timing cover to read the front harmonic balancer.
What setup do you have? What intake manifold are you running?
-Donny

 

First thing to do is that compression check!!!! If that checks out ok you can forget the rest of this. I STRONGLY suspect it is still an EFI problem.

 

I would do compression test, leakdown test, combustion gas test. Good luck!

 

Are you positive that you do not have a bad vacuum advance canister?
You could have a vacuum leak from the advance canister, intake manifold gasket?

 

I've never seen a head cracked enough to effect idle without some other indicator.
I would drop the carb back on there and see what happens. You can disengage the fuel pump and feed it with a can and siphon above the inlet level. If the surge goes away, that would indicate an issue with the EFI.

My EFI knowledge is sparse at best so:
A surge can be caused by:
Issues with the mapping
Issues with the O2 sensor (or any further sensors you have)
Bad electrical connection(s)
Exhaust leak sucking air into the system
Surging fuel pressure.
Issue with the TBI construction

 

EFI uses the crank or tach signal to time the injector pulses and map into the fuel lookup table. Even fuel-only systems need a trigger signal. Seems most likely that the odd-fire tach signal is messing with the injector pulses to some degree. Does Holley say specifically that the Sniper is ok for odd-fire engines? Or is this a system that is sold specifically for the odd-fire V6? Seems reasonable this uneven pulsing would have the most effect on performance at low speed.

 

Thanks for all the input. I am going to start trying to rule out some of the leak theories because Holley and tuner keep thinking that is what is going on. The tuner is still trying stuff, but says he has encountered this issue before and it ended up being a small crack in head.

It’s an odd fire v6 with the small hole 2gc sniper.

Rpm- have a Hall effect sensor with the crank trigger so I get a uniform tach signal.

Vac canister - I have a new dui distributor on order which should ship today or early next week… hopefully if it’s a leak or advance issue that will resolve it.

I have chased down and hopefully resolved exhaust leaks using positive pressure and soap suds, but I am going to smoke test the exhaust to make sure.
I have done the starter fluid trick around the various ports to see if rpm increase, but I am going to try to get more precise.

Fuel pressure - I have moved to an external regulator and removed snipers internal one so pressure fluctuations have been ruled out (I think).

I am realizing efi needs very constant variables and a squared away fuel/timing/engine to work well, whereas a carb can fudge less than ideal conditions much better.

I’m off to run suggested tests and will report back.

 

I ran the sniffer test with the bulb and the chemical: I could only squeeze the bulb a few times before it made a vacuum and wouldn’t draw anymore, but it didn’t change color. Engine was at temp and idling and thermostat was open.

I also ran a hot compression test: 165, 125, 150, 175, 175, 180. The low cylinder is on the driver side, and the 02 sensor is on the passenger bank exhaust before the collector. I didn’t run a cold one…would that tell me anything different?

one of the spark plugs was rust color brown, the rest looked like they were supposed to. It was on the passenger bank with the 02 sensor and was gapped alittle more than the rest. I replaced it with a new one and a correct gap and confirmed it worked…after driving around I took it out and it looks like it is supposed to now.

the tuner sent me another tune and fiddled with it. The surging idle still comes back intermittently.

smoke tests and leak down test next?

Is there a more exact way to tests for vacuum leaks at the throttle body base or other places than just the starter fluid method?

 

Did a smoke test on the intake and exhaust. The only leak was a major one at the clamp-on 02 sensor. That could be the cause of my woes if it is sucking in fresh air….now off to find some one to weld on an o2 bung in a tight spot. I’m really hoping that is it.

no leak down test yet…I can’t find a loaner or cheap one and frankly I don’t know what I would do if I found a big issue in a cylinder or valves.

 

The O2 sensor leak will absolutely affect your tuning big time. The "computer" is trying to compensate for what it thinks is a lean condition and no doubt dumping more fuel in. It actually doesn't take much of a leak there to cause problems.

 

Well I updated on my build page cayennes calamity that I have become pretty confident the tuner is right.

I am strongly considering pulling my heads this weekend and sending them for rebuild.
I am also going to see if Sal at vintage jeepster can rebuild the rocker arm assembly while that’s off.

Is there anything else I really need to do while I am that far in the engine? Cam, timing gear? Etc? I would rather not replace the cam unless it looks all chewed up or scorched.

I have been studying the field manual and books, but if there are any hints or warnings I would love to hear them.

i ran it for the first few years with the timing out of sequence (I didnt realize how important having the wire on the right distributor terminal was since it was odd fire). I think that may be coming back to haunt me.