VG30 Timing / No Power Issue

[SkiMachine]

Hello,

 

I have a 1994 4x4 A/T VG30 Pathy that has a few issues. The one that I've been chasing the most is a low/no-power issue for the past few weeks. I seem to have tracked it down to being a timing issue, however I can not advance the timing enough to bring it back into spec. It's currently sitting at 5ᵒ BTDC, when spec is 15ᵒ BTDC. The distributor is turned to it's limit, and is quite a bit off from it's original setting.

 

This issue has been progressive - the truck had been steadily loosing power day by day until I decided to adjust the timing "by feel". I don't like to adjust timing by feel, but I didn't have a light at the time (do now!) and the truck couldn't get moving from a stop any more. Obviously the timing was as retarded as that kid who skipped class and sniffed glue all day back in school. With the timing at 5ᵒ it can at least get moving.

 

So, what causes this? My first thought was that the timing belt on the LH cam or crank pully jumped time, but this issue has been progressive so this seems unlikely. The only other possibility I can think of is that the ECU is on glue as well, but that too seems unlikely.

 

Background and what has been checked so far:

 

- Purchased last fall, NO service history

- Timing belt age is unknown, but (until this issue) was very high on my agenda to replace.

- Most sensors seem to meter out O.K, even at the ECM (at least according to the FSM).

- It has the standard exhaust header stud failure and resulting leaks, but they've been there the whole time...

- I'm not 100% about the O2 sensor, but this shouldn't be an issue at idle anyways since according to the FSM the ECU runs in open-loop mode at idle. I'm not sure about it because I do not get a code when I unplug it.

- EGR valve appears to be in working order.

- Fuel filter and air filter have been changed

- Idle (according to the tach) is at 750.

- Replaced the plugs and wires (had to, old wires broke when doing the balance test!)

- Found and repaired two small vacuum leaks. The hoses are (as expected after 20 years) very brittle so there may be more leaks.

 

It may be worth noting that the transmission also needs a re/re/re since reverse very recently stopped working. I don't see how that could be affecting the lack of power/timing issue though. I'd expect power loss in the transmission to present it's self as slipping, or lots of bad noises and smoke.. I don't think there is any noticeable slippage despite the reverse gear issue.

 

I want to make sure the performance issue is fixable before committing to pulling the transmission out or drilling out the broken studs.

 

Any ideas?

Edited May 15, 2013 by SkiMachine

[Nefarious]

Maybe your distributor is just off a tooth? Has it always been like that or is this a new symptom??

[Trogdor636]

Codes?

[SkiMachine]

Ahh I knew I forgot to mention something. I had a knock sensor code, but replaced it. It's not mounted to the block yet (will relocate it due to lack of access), but it is grounded. Code is gone with no improvement. No other codes, other than ones I've intentionally caused while testing.

 

The truck ran fine up until a few weeks ago.

Edited May 15, 2013 by SkiMachine

[Precise1]

- I'm not 100% about the O2 sensor, but this shouldn't be an issue at idle anyways since according to the FSM the ECU runs in open-loop mode at idle. I'm not sure about it because I do not get a code when I unplug it.

Yeah, the O2 sensor won't always throw code....

The curious part about this is the gradual change, it makes me think that the ECU is receiving progressively erronious information. The ECU does affect timing as well, have you checked the crank angle sensor? Also when checking sensors, make sure to inspect any connectors and fiddle with the wiring when it is running to see if there is a change. I've run into this on a few Pathys, the wiring isn't what I would call robust.

 

It may be worth noting that the transmission also needs a re/re/re since reverse very recently stopped working

Don't drive it until you check to make sure there is flow through the cooler. What is the fluid like?

 

B

[SkiMachine]

If it walks like a duck and quacks like a duck...

 

It looks like I've jumped time by 2 teeth (on both cams, thus 1 tooth on the crank). This is with the upper TB cover off, using the crankshaft drive pulley's TDC mark. The belt isn't slack but probably isn't at full and proper tension either. No missing teeth or obvious belt damage so I'm surprised it was able to jump. Both cams are off equally so this must have been a crank sprocket jump.

 

My math indicates this is retarding my valve timing by 18ᵒ. The FSM indicates the exhaust valves close at 10ᵒ BTDC.. I'm hoping the valves are already well on their way to being closed at the 18ᵒ point and nothing collided.

 

I'm still not sure why this felt progressive. The only thing I can think of is that there was/is another parallel issue that started to inhibit the truck's ability to deal with the valve timing problem.

 

All of the cylinders (except 1 and 6) are @ 90psi on the compression test. Cylinder 1 was at 120psi, and I didn't bother with #6 since the results were pretty conclusive by that point. I did the wet test on #1 and #3, which improved compression by ~ 10psi each. Lower compression with bad valve timing seems about right, but I'm a bit concerned that #1 is so much higher than the rest.

 

The plan now is to pull the lower TB cover, correct the timing, and then re-do the compression test to see if this engine is worth any more effort.

[Precise1]

Just the fact that you have compression is the important part. Definitely replace the belt and then test again to get another set of data points but I'm pretty sure everything is fine, especially if you were just one tooth off.

How many miles on the motor?

 

B

[devonianwalk]

I feel like a broken record repeating my timing jump issue so, I'll save the details. Mine jumped as much as two teeth on one cam and one tooth on the other. I had slack between the cams! I still have good compression on all cylinders. You are probably fine.

[Slartibartfast]

The FSM specifies compression at between 173 and 128 psi, with a limit of 14 psi difference between cylinders. It's possible that the valves are just opening and closing so far out of time that compression is down, but I have no idea why #1 would be so much higher. +1 on holding off judgement until it's timed right.

 

I'm just amazed that it runs at all!

[Alkorahil]

I feel like a broken record repeating my timing jump issue so, I'll save the details. Mine jumped as much as two teeth on one cam and one tooth on the other. I had slack between the cams! I still have good compression on all cylinders. You are probably fine.

 

 

Its all about having good timing!

(seriously no pun intended)

[SkiMachine]

I think pictures will tell a thousand words on this one.

 

This didn't look too hopeful... :

 

 

 

 

When disassembling I noticed that the drive pulley could be turned a bit without the timing belt moving, so I knew something was up right away. This also explains why the issue was progressive in nature. As for cause? I'm not 100% sure, but the crankshaft bolt was really loose (ie: wrench NOT required for removal) so it could be impact as the gear wobbled back and forth.

 

There is some marring on the timing gear (see first picture, I'll upload a close-up tomorrow). I'm not sure if something got jammed in there, or someone scratched it up with tools in the past (ie : the guy who didn't torque the crank bolt down properly).

 

Either way it would have taken a serious hit to have caused that kind of damage to the crank. I'm at a complete loss for on-vehicle solutions to this one. Anything I can think of involves tearing down the engine, and a trip to a machine shop. At the end of the day, this is a 20 year old car, with 219,000km and a transmission that also needs rebuilt.. I'm going to have to think about my next step.

[Precise1]

Damn, that isn't good, but does explain a lot...

 

Redpath88 did an on vehicle repair to his crank snout which I believe consisted of cutting a new keyway at 180* and indexing the pully, so it can be done.

Wrong, fill weld and regrind seems to be the only way and Red bought different motor. So much for my memory...

 

B

 

Some links

http://www.nissanpathfinders.net/forum/topic/31036-broken-crank-keyway/?p=587580

http://www.nissanpathfinders.net/forum/topic/31078-crank-snout-woodruff-key-question/?p=588473

http://www.nissanpathfinders.net/forum/topic/21986-rolled-crankshaft-woodruff-key/?p=387532

Edited May 28, 2013 by Precise1

[SkiMachine]

Why would cutting a new keyway at 180 degrees not work? Too hard to get the measurement right or does it screw up the balance? Just curious.

Edited May 28, 2013 by SkiMachine

[SkiMachine]

I do have access to a 120V arc welder with 5/64 and 1/16 electrodes, but not sure if that can really fill-weld.. It's been a long time since I've welded anything.

[Precise1]

I'm not a welder at all, but I do know you would want to use fill rod and go slow/low amp as not to overhear/warp the crank snout. The good news is there isn't a lot that has to be filled. Maybe something you have 'pro' come and do on site for you?

 

Why would cutting a new keyway at 180 degrees not work? Too hard to get the measurement right or does it screw up the balance? Just curious.

Yes, that was my initial thought, that it would be hard to hit 180 dead on. Upon more thought the pully would have to be perfectly symmetrical with an even number of valleys as well. it might not be realistically possible.

 

B

[SkiMachine]

Finally got around to working on this some more. 6 day work weeks, hockey playoffs, and being bicycle distance to work, amongst other things kept me from getting back to this.

 

We ended up welding the TG woodruff key in place. I changed the oil seals, belt, tensioner, put it all back together and now it's running smooth with plenty of power. Compression is now ~ 175 +/- 5 or so psi across all cylinders which is pretty much dead on spec.

 

The old woodruff key was completely destroyed, there was maybe just 1mm or less metal left before the timing gear would have been free-wheeling...

 

As for why this happened? I think whoever said (in one of the threads linked by Precise1) that the woodruff key is just for indexing and it's the crank bolt that's supposed to hold everything in place is correct. Whoever said the woodruff key is too short is also correct, IMO. With the woodruff key fully pressed in there was at least a 2mm gap between the top of it and the bottom of the TG index slot. Obviously centerfugal force would migrate the key fully up into the TG over time leaving even less contact with the crank shaft. The crank bolt not even being finger tight just sealed the deal. My best guess is the previous guy in there just used a rattle gun to tighten the bolt, didn't lock up the crank shaft while tightening (I made a crude tool to do this), or both.

 

So now on to the autotragic.. The fluid looks black, or at least dark brown to me..

Edited June 28, 2013 by SkiMachine

[Slartibartfast]

Good that you got to it before the key gave up! I almost want to go check my crank bolt now.

 

Black tranny fluid is not good. Get that out of there asap, and look at getting a new tranny cooler for it (probably best to assume the one in the radiator is gunked up). Hopefully the reverse issue is just a stuck valve and not a worn-out clutch pack.

[ThaBigPerm]

Why would cutting a new keyway at 180 degrees not work? Too hard to get the measurement right or does it screw up the balance? Just curious.

 

Depends on the engine. Not sure if a VG30 is internally or externally balanced, but old-school small block Fords and Chevys are externally balanced, using weighted flywheel and harmonic balancer to balance the engine. A giveaway that an engine is externally balanced is if the harmonic balancer has unilateral "lobes" of extra material, or material is drilled/milled out favoring one side or the other.

 

A few examples of what you'd see: