code 91 92 & 93 but its the number 7 cylinder

[kevin77]

My 1994 suburban started running rough - I replaced the injector pump and injectors 1 year ago. I start the truck up, it idles fine. I run a cylinder balance test with a tech 1 and all of the cylinders are firing. I gun it, and it starts running rough and I get dtc codes 91,92 and 93 - cylinder imbalance #1, #2 and #3 cylinders. I run a cylinder balance test and I turn #7 cylinder off and it runs a little smoother and the rpms go up a little.

I at 205,000 miles - about 10,000 on the pump and injectors. I've been treating fuel and I checked the fuel filter and it was fine. Also, when I am going down the road and accellerate I hear spark knock -

I checked alldata and either I replace the dual mass flywheel (I have an automatic) or check compression, fuel deliver, injector or ip pump - can anybody send me in the right direction?

(plus we are suppose to get anywhere from 4 to 12 inches of snow tonight)

Kevin

[DmaxMaverick]

Check all your return lines first. If one is plugged or kinked, it will cause injector(s) to misfire. Then....

Switch the #7 injector with the #2 and test again. If the problem follows the injector, the injector is bad. Not uncommon, even when new. If it stays with the cylinder, you have a compression/valve/gasket/etc. issue.

[kevin77]

I switched out the injector for cylinder #7, got her warmed up and the cylinder balance test still points to #7.

When I drive it up to 55 mph, I can hear a knocking and intermittent smoke - kinda like it wants to fire does and does not. Once I slow her down from 55 and park her, she idles fine. If I gun it and let off, she will then idle rough.

Whats next - compression test, heads, motor?

Kevin

[Robyn]

Check the compression on number 7 and if its reasonable then its a fuel deilivery issue.
My eye is looking at the IP and or possibly the PMD at this point.
You could very well have one plunger fouled up.
Before you spend loads of dollars try a different PMD and if that fails to solve take the IP to a reputable shop and have them test it on a test bench.
There are a few internal issues that very well may be the problem.
Just because it has been rebuilt does not always mean it will work for a long time.
Hope this helps
Robyn

[kevin77]

We ran a compression test on #7 - the first time we could get itpumped up to 400 psi but it would not hold the pressure.

The second time she would not even pump up. Nada. no pressure - you could hear it when she was cranking too - it almost sounded like it was trying to fire on one cylinder (pmd disconnected) when it found no resistance on #7.

205,000 miles (got it about 160,000) and the only time she ever let me down is when I put some bad fuel in her and the fuel line froze up (my fault!)

I think it is the rings.

Kevin

[gmctd]

Or an intake valve stuck open - when you killed #7 injector, the cylinder mix was less dense, so less load on the other cylinders.

Pull the odd-bank valve cover, check the nylon rocker-arm keepers - also be a good time to do the ones on the turbo bank - they darken and crumble way B4 the driver's-side bank pieces.

[Robyn]

Sorry to hear the news
Have a helper work with you and crank the engine over with the IP shut down.
Listen at the tail pipe and then the air box. If you hear hissing, chuffing or some strange noise you can more correctly diagnose if its an intake or exhaust valve. With it running an intake issue will cause a chuffing noise in the air box.

As previously mentioned the rocker arm guides can break and allow the rocker to slide off the valve.
Unfortunately to get the rocker covers off you need to remove the high pressure lines from the pump which also means the intake has to come off.
(DONT BEND THE LINES)

When removing the lines, make a kewl little map of the back of the pump and which lines go where.
DO NOT seperate the lines from the mate they are with (Two line sets)
Keep them together and remove in sets and mark at least one of the lines so you know where the set went.
Cover the pump and injector outlets with a caplug or at least a wrap of duct tape after wiping the fuel off. Dirt is not something you want in there.

When you remove the intake you will find the little sheet metal clips that hold the fuel lines, keep them and do reinstall as they perform a valuable function.

Check things out and get back to us

Best to ya and good luck with the fix

Robyn

[kevin77]

I pulled the valve cover off, removed the rockers and it is

A broken valve spring.

Can I replace just the spring or is this an indicator of a larger problem?

Kevin

[DmaxMaverick]

Oooh. Tough choice.

With those miles, you really don't have much to lose. What I'd do is have a shop scope the cylinder. Make sure you don't have a cracked piston or serious valve damage. If it looks OK (even marginal), I'd put a spring in and do a compression test. If it works, you get out cheap. If not, well, you would have pulled the head anyway.

[kevin77]

Here is a look at my spring

http://www.thedieselpageforums.com/photopost/data/500/medium/broken_spring.jpg

[Robyn]

A broken spring is not the end of the world.
If the engine was not making bad metalic crashing noises I would try a new spring.

Was that an intake or an exhaust valve??
Most likely the spring was just weak enough after breaking that it was not sealing well enough to hold the compression.
Also can you move the valve up and down??
If you air that cylinder up from a compressor and the valve will seal and hold it's a good bet you are going to be ok.

If the valve smacked a piston though its probably toast.
You said that it would idle OK ?? if this was the case I would feel ok about fixing the spring and getting on with it.

Fish all the broken pieces out of the valve train area.
You can roll the engine untill the valves should be closed and air up that cylinder with an adapter through the glow plug hole to hold the valves shut Now you can install a new spring.

Look over the rocker arms and as was mentioned earlier replace the plastic buttons with new ones.
Make sure the push rod was not bent, The push rods go in with the copper colored ball to the top end.

Caution when you tighten the rockers down do it slowly so you don't stuff the valves into the pistons.
Its best if you can get the pistons so they are down a little in the holes before you tighten the rockers back up.
After the rockers are back on roll the engine BY HAND slowly to make sure you dont have an valves hitting the pistons.

Button the sucker back up and you should be good to go

[Robyn]

In looking at the pix I see that it is an exhaust valve and also that the rotocap and keepers are still right where Ma Chebby put them, this is a good thing.
What was happening with the bad spring for all intents and purposes was valve float to some degree. At speed the spring was so weak that it could not keep the valve sealing and at idle it could, this explains why it would idle on all 8 and miss badly at rpm's above there.

I am not real nervous about this engine. Unless there are other things that we dont know I would bet this little diesel rat will run fine with a new spring.

Good luck
best to ya

Robyn

[Warren96]

I was lucky when this happened to mine 80,000 miles ago.What i did was ; I removed the valve cover revealing the collapsed lazy spring,turned the engine over BY HAND until the piston pushed the valve as far shut as posible,then you can dissasemble the valve keepers retainer and pieces of the broken spring, and the valve can't fall into the cylinder.You will need a small valve compressor to get the new spring on. Then put everything back together and double check everything.I didn't even need a garage, mine was done in the driveway.The last thing i did was i said a little prayer to the 6.5 god and promised to take good care of this engine. And then i fired it up. Good luck and let us know how things are developing!

[JohnC]

Here is a look at my spring

It'll never run right. The engine's in upside down! ;)

[kevin77]

My brother-in-law and I were taking a closer look at the valves on #7 and it looks like the intake valve dropped a guide - there is a lot of side-by-side play on the intake valve - we are going to pop the head off and take a good look at the condition of the cylinder - I sould know this weekend what is going to be needed.

Kevin

[kevin77]

Looks like the cylinder took a bit of damage - I made the picture big so we could see the damage in detail - I don't thank I can leave it this way - Opinions?
(and yes, the date is wrong on the camera)

But I have the picture right side up this time ;-)

Kevin

http://www.nationalplazas.com/100_1518.jpg

[gmctd]

If no cracks in that piston or the others, you could repair the head and go back with it and a fresh timing chainset - those dents probably will not give any further trouble - or replace that one piston.

Or, at 205kmi you could also do a complete rebuild

[Robyn]

The small dings down by the lower edge of the piston were not caused by the valve striking the piston (Wrong location) The precup sits right where the dings are.
Possibly some junk from a previous close encounter??
If the valves had struck the piston they would have done serious damage and bent pushrods and such.
Roll the engine over and get the piston down so you can see the cylinder wall.
If the wall is good and shows no sign of scoring I would clean it up and stuff it back together.

The head of the piston is very thick and the small dings I see in this pix are not real disturbing. From the top of the piston to the top ring is about 3/8"
and the top ring groove is a steel insert so I doubt that the ring was bothered.

If you have head issues, might as well fix it at this time though.

In thinking about the damage, its possible someone broke off a glow plug at some time in its life and the sucker beat it up and blew it out.
Or maybe some other junk got ingested during a time that the top was open.

Good luck
Robyn

[Robyn]

To my knowledge these engines never had replaceable valve guides.
What you have is most likely just a badly worn out head.
I would replace the heads with a fresh set from "Clear water cylinder head"
They will send you a new set YES New castings for under $700 and then they pay the freight to get yours back.

What I am told is that they use a new casting and many good used valves and springs as long as they meet spec.
The set I got looked like all new parts but I cant be absolutely sure

I used a set on my 94 and they are nice heads.
I have been told they are China castings but also I have heard they are New Zealand castings and I dont know or really care.

The quality was great and they are working fine.
The new heads weigh about 8 pounds more than stock.

OH BTW be sure to get a new set of head bolts. THE 6.5 use a TTY bolt.
YUP once through and ya toss em.
Set is about $40

The pushrods go back in with the copper colored end up if you did not already make note of that.

I think someone already mentioned "New Rocker Guide Buttons"
Do it, they are cheap


I think you had been running that engine with the dings in that piston a long time, at least as long as you have owned it.

[kevin77]

I re-read the article on MPG on the 6.5 - I don't do any heavy towing with my 6.5 - doesn't Pennisular have some high mpg heads?

Kevin

[gmctd]

Any head would be a hi-mileage type with the correct pre-cups installed - that and have your right boot re-soled....................

[kevin77]

Any head would be a hi-mileage type with the correct pre-cups installed - that and have your right boot re-soled....................


Does that mean loss of power? I called and talked to Matt at pennisular today and had a nice discussion about the 'miser' heads that he sells - yes they increase the velocity of the air in the precup, increasing the mixture of the fuel and the air - as it said in the milage article on the 6.5 a couple of months back - but there is a loss of horsepower associated with that.

As always, it is a trade off - has anyone tried the smaller precups on a 6.5? I'm toying with the idea of lost power vs. higher mpg's - the best milage I have gotten was about 16 on a 4x4 K2500 suburban. I tow rarely.

I'm trying to decide if I want to be an experiment...

Kevin

[gmctd]

The "S" emissions\economy engine has smaller pre-cup ports than the "F" engine

Diesels generate torque at low rpm, good for towing, fuel economy - horsepower is is a hi-rpm thing, good for the oil companies