Broken Motor??

[WyoSyclone]

Well, the weather was great tonight when I got off work, so decided to go for a drive in the Sy. I tuned all last weekend and was looking for a really good DM run to do the last fine tuning on the VE's. Running 18lbs boost on pump gas, timing backed WAY down to stay away from knock. I did one short blast through 1st, 2nd, and 3rd (felt great)... cruised down the road a little bit, turned around did another short blast, turned the corner on to the straight away headed towards our house and did a third blast from a roll through the top of 3rd gear. Before this last one I looked at DM and my IAT's were still right at 80 degrees f. - pretty chilly out still.

Well, drove along for about a mile then it started to sound like the engine was just 'off' a little. Gave it a little boost and it just didn't seem right. Got home, pulled the plugs and they all look fine, did a compression check - turned out ok - 170, 170, 165 on 1,3, and 5. 166, 169, and 165 on 2,4, and 6. There are no bubbles in the coolant, exhaust smells good, nothing in the oil.
But, it is missing.. the only way I can tell is I have the passenger side tire off and fenderwell out for the plug change and I can bend down with my head in the fenderwell and hear a miss when I rev the motor.. this isn't a hard miss that you can hear in the exhaust, more of a muffled miss... maybe a bent rod?? God, I hope not.... I don't have the place to tear down a motor. I pulled the plug wires off at the rotor and it seems that #2 makes the least difference.
Causes??
- bent rod (I don't think compression would be as good as it is).
- bad injector?
- bad plug (even though they all look great).
- bad plug wire?
- valvetrain sounds quiet

Any other thoughts??

Thanks guys,
Rob

 

[WyoSyclone]

Re: Broken Motor??

Blown-out intake manifold to cyl head gasket on the bottom where you can't see it?

I agree, compression would be lower with bent rod. From this post, it looks like you know what you're doing. If it didn't detonate hard, it didn't bend a rod.

You did say 18psi. I like the intake gasket failure idea.

Yes, that's a good thought, Dave... I'll pull out the rig I made to pressurize the intake and see if I get any leakdown.... I'll smell the oil too.. see if it smells like any gas may have gotten in. Thanks...

 

[TYTILIDIE]

Re: Broken Motor??

You know Rob, when I get really into tuning, I forget about how much the trucks eat ignition components. Everytime I have doen a tune up, everything has looked great even though it clearly ran progressivly worse. First things first, Ild change your plugs wires blah blah and see if it goes away. I hope you get this stuff where they are warrantied. I get mine at Autozone. Wires are warrantied. Have to buy everything else, but still, thats half the cost.

 

[Foot Performance]

Re: Broken Motor??

Yeah no bent rod the different compression readings probably just temp change for time of start.

Vacuum leak is possible look and see if the truck starts to lean out possibly. You could also plug all the vacuum connections to the crankcase pcv valve ext (not sure if there are any more vacuum connections) and then with the crank case sealed use on of the ports in the valve cover and hook it up to a vacuum gauge and then if it is sucking air it should show on the gauge(seen dodge motors with a plate on the bottom of the intake leak and this works pretty well)

Injector probably the same thing.

Plug and wire could be switch from cylinder to see if the miss moves.

Valve train should have showed up on the compression test as well.

Let me know if you need some help(if i can help)
Brandon

 

[WyoSyclone]

Re: Broken Motor??

You know Rob, when I get really into tuning, I forget about how much the trucks eat ignition components. Everytime I have doen a tune up, everything has looked great even though it clearly ran progressivly worse. First things first, Ild change your plugs wires blah blah and see if it goes away. I hope you get this stuff where they are warrantied. I get mine at Autozone. Wires are warrantied. Have to buy everything else, but still, thats half the cost.

Yup, that's a good thing to think about too... this Sy still has the KB plug wires on it.... I'll do a resistance check on them tomorrow and see if one has an open, or too high of resistance... I remember seeing a thread somewhere here where someone listed the resistance of 3 or 4 different brands of plug wires. The NGK plugs only have about 50 miles on them.. I'm getting great spark out of the distributor... did you guys know that spark can jump about 4 inches right into your finger when you pull the plug wire off??

 

[WyoSyclone]

Re: Broken Motor??

Yeah no bent rod the different compression readings probably just temp change for time of start.

Vacuum leak is possible look and see if the truck starts to lean out possibly. You could also plug all the vacuum connections to the crankcase pcv valve ext (not sure if there are any more vacuum connections) and then with the crank case sealed use on of the ports in the valve cover and hook it up to a vacuum gauge and then if it is sucking air it should show on the gauge(seen dodge motors with a plate on the bottom of the intake leak and this works pretty well)

Injector probably the same thing.

Plug and wire could be switch from cylinder to see if the miss moves.

Valve train should have showed up on the compression test as well.

Let me know if you need some help(if i can help)
Brandon

Hey Brandon, thanks for the insight on the truck leaning out.... I just remembered that when I started it up after checking the plugs and compression that my WB was reading 17.... has been running right at 14.7 to 14.9 at idle. Hmmmm, sounds like we're on to something guys.... arggghhh, I don't look forward to taking the intake off. Thanks for the offer, too, Brandon... might take you up on it.. wonder when we're going to do Dave's Sy?

 

[NecroWolf]

Re: Broken Motor??

did you guys know that spark can jump about 4 inches right into your finger when you pull the plug wire off??

:tup: :rotf: :rotf: :rotf: :rotf: :rotf:

 

[SY2932]

Re: Broken Motor??

I remember seeing a thread somewhere here where someone listed the resistance of 3 or 4 different brands of plug wires.

Sounds like Richard Lee's misc info page. One trick that I have used in the past to isolate a miss to a particular cylinder is observing the light from the pick up on a timing gun. Let us know what you find out...

 

[WyoSyclone]

Re: Broken Motor??

Sounds like Richard Lee's misc info page. One trick that I have used in the past to isolate a miss to a particular cylinder is observing the light from the pick up on a timing gun. Let us know what you find out...

Hey Mike, thanks for that link... I'll try that with the timing light... I also picked up a Snap-On inductive spark tester off of Ebay a while back - is supposed to tell how much energy is being passed by each plug wire.... I'll see if either of those two tests provide anything useful - may help someone else diagnose in the future.

 

[Flyin Ryan]

Re: Broken Motor??

I'm gonna get my bets in now... and go with the intake gasket helping to make a nice vacuum leak

 

[turbodig]

Re: Broken Motor??

Sounds more like a gorked plug/wire to me... I'd go down that road first.
Tuning kills ignition parts, at least until you get stuff dialed in better.

 

[TYTILIDIE]

Re: Broken Motor??

I agree with Dig, I would imagine that your idle would be sky high if your intake gasket was trashed enough to put your AFR in the 17's.

 

[Foot Performance]

Re: Broken Motor??

I agree with Dig, I would imagine that your idle would be sky high if your intake gasket was trashed enough to put your AFR in the 17's.

Very true I forgot about the higher idle :tup:

 

[turbodig]

Re: Broken Motor??

Hey Brandon, thanks for the insight on the truck leaning out.... I just remembered that when I started it up after checking the plugs and compression that my WB was reading 17.... has been running right at 14.7 to 14.9 at idle.

Well, there's your miss.... a 17.1 ratio would do that.

I'd check to see if you have a split-open intercooler hose.. would cause the loss of power and the vac leak/lean condition.

*EDIT* Duh... an IC leak wouldn't leak vacuum.

All the same, a hose could be split open elsewhere.

 

[TYTILIDIE]

Re: Broken Motor??

Have you had a big change in temps there where you live? Just a though.

 

[WyoSyclone]

Re: Broken Motor??

Wow guys, you almost have me excited about finding the cause of this

I guess the question I'm asking myself is.. with the afr's at 17 at idle, my idle is still at 875 to 900 (normal for my Sy)... would one cylinder not firing change the afr in that manner? Seems like it would almost make it run a little rich, if anything..... one of the reasons I thought I may have had an injector go bad. But, being batch fire it seems like it should still fire (maybe it is and that's why it is seeming to be a 'soft' miss).

I'll hook up DM tonight and look at my IAC counts at idle and compare them with another, earlier run... I don't know if the IAC is capable of making that broad of an adjustment for a major vacuum leak.

I don't think it's a ruptured hose, cuz the engine definitely has a miss just off of idle that seems to be accompanied by an out of balance condition (all the hoses are upstream of the throttle body).

I'll test the plug wires first tonight, then I'll hook up my rig for pressurizing the intake tract and see what happens.

Thanks for all the input...MUCH appreciated!

 

[turbodig]

Re: Broken Motor??

Wow guys, you almost have me excited about finding the cause of this

I guess the question I'm asking myself is.. with the afr's at 17 at idle, my idle is still at 875 to 900 (normal for my Sy)... would one cylinder not firing change the afr in that manner? Seems like it would almost make it run a little rich, if anything..... one of the reasons I thought I may have had an injector go bad. But, being batch fire it seems like it should still fire (maybe it is and that's why it is seeming to be a 'soft' miss).

I'll hook up DM tonight and look at my IAC counts at idle and compare them with another, earlier run... I don't know if the IAC is capable of making that broad of an adjustment for a major vacuum leak.

I don't think it's a ruptured hose, cuz the engine definitely has a miss just off of idle that seems to be accompanied by an out of balance condition (all the hoses are upstream of the throttle body).

I'll test the plug wires first tonight, then I'll hook up my rig for pressurizing the intake tract and see what happens.

Thanks for all the input...MUCH appreciated!

Also, a big enough vac leak would show up as high idle map.

 

[autoaddictions]

Re: Broken Motor??

After i poped my head gasket and fixed it my ty had a miss. It pissed me off to no end turned out to be a bad distibutor cap. It looked fine but after changing the miss was gone. I was thinking the worst bent rod or cracked piston bad injector. Check the cap and rotor. By the way my cap and rotor that was bad only had 500 miles on it.

 

[WyoSyclone]

Re: Broken Motor??

OK Guys.....drum roll please


I got home tonight and decided using a multimeter was the fastest way to start doing some diagnosing... since I 'thought' it was related to the right side of the motor, started at #2 plug.... OK, 645 ohms of resistance... not bad.... then, on to #4....

As Scooby Doo would say.... Roh, Roh...

Let's see if we can find out what's wrong by methodically doing surgery on this cable... first, let's slice the boots off and see if there's an open right at the snap ring.... Holy Cow, Batman!

Wonder how good of connection this has been making for the past how many miles? :squint:

So, it's off to find a set of Taylor wires tomorrow... plus a new cap and rotor.... may as well replace the 50 mile old Iridium NGK's while I'm at it.

Thanks for all the input guys.... just discussing a few things really lets a person calm down and think rationally about things....

....Dig, how do you do it... psychic SyTy man....

FYI - These are a set of the old Kenne Bell Red Hot 8mm wires.... nice quality control!

 

[Try Me]

Re: Broken Motor??

Everytime i would have trouble with mine the first place i would go was plug wires. with the ATR headers it used to have it was a tight fit and i would have one burned up all the time. dont spend $40 bucks on a set of "made to fit" wires. order a 25' roll of msd 8.5 mm wire and the summit brand crimp tool. Youll have at least 3 sets of wires that you can custom make and route as you please and you are your own quality control! In the 3 years i had the truck with the 4.3 in it, and after 40,000 miles, i replaced the cap and rotor ONCE!