Non-Mercedes 6.5 GM diesel problem
 

Got a thread on this over at the 6.5 forum at Diesel Place but I thought I'd pick people's brains here too. About 3 weeks ago I bought a 93 GMC Sierra pickup with a 6.5 turbodiesel and 104k miles. Started it cold and hot before purchase. Fired right up. Finished up the third of tank of fuel that was in at purchase, filled it up and ran 400 miles on that tank. Filled up again. Immediately it began showing symptoms of harder starting and 130 miles later it is extremely hard to start when hot. It does start if I pour water on the IP to cool it down, which is the standard test for a worn out pump on these IP's. But I'm suspicious of that diagnosis since the hard starting occurred immediately after filling up. I've replaced the fuel filter. Glow plugs are controlled by a temp sensor in the engine and don't operate once the engine is up to temperature. I installed a fuel pressure gauge and lift pump is providing about 7-8psi all the time. Bleeder valve shows plenty of fuel when cranking or running. I was wondering if I got a tank of thinner winter fuel and it showed up the problem of a worn pump right away over summer fuel. Other than the hard starting it runs fine.

Do you have the remote mounted heatsinked PMD on it?

No, it's a mechanical pump. DB2.

Glow light is not working during the hard starts, but the whole time I've owned the truck, the glow light has stopped coming on once the engine is warmed up, even prior to the hard starts. I'd been told that was normal on a GM 6.5.

From what I dimly recall of mechanic school a dozen years ago, no glowing when hot is a "feature" of the 6.5. Sounds like you have a bad pump. Last time I checked Stanadyne rotary pumps were relatively inexpensive. That one should have lasted longer, but maybe it was run on petrol or other bad fuel before you got it.

The glow plugs usually cycle some while the engine is first running. The temp sensor can be faulty and cause short glow cycles. Combined with a few bad glow plugs this can cause a hard start. But a good 6.5 in mild weather usually starts with minimum amount of heat anyway. Glow plug problems show up when the engine gets cold.

Cranking speed OK? Diesels hate cranking slowly. Hot starters can slow down. I'm sure you'd recognize that.

Air leaks occurring due to temp change when engine's warm? Clear return hose on IP can help identify air intrusion issue.

Problem occurred after fill up, leads me to wonder if this is an existing problem the PO discovered a way around with a fuel additive. I used to work on a 6.2 powered truck that had fuel which always smelled a bit like gasoline. Owner was adding gas to help a hard start. Yikes!

It's possible to connect an injector to the injection pump to observe pattern and flow. Also, watch the return line from one bank of injectors. If no fuel during crank or mostly bubbles, and air is not the culprit, expect to change pump.

Glow light does cycle a few times after starting when cold so I think it's working correctly. I haven't ohmed out the glowplugs but it seems to start ok when cold. Starter speed seems fine. It's definitely not turning any slower when hot than when cold.

'97 6.5 ds-4 owner here
 

100% operational glow plugs are important, and the older glow plugs have
a nasty habit of swelling and getting brittle, breaking off while removing.
So check that all 8 have the spec resistance, the connecting wires
are clean, the oil pressure switch (if your older motor has this) and the
glow plug relay are good. Also, do a proper load test on the batteries.

Re. fuel delivery, air in the lines can be devilish. Try cracking some injector
connections loose to get some extra bleeding. and check that fuel return
lines aren't kinked or crummy. Your fuel filter is different from mine. Does
it have a built-in collector for water? drain that thing.

Good luck. It took me 2 years, several PMD's, finally 1 remote PMD, 1
lift pump, and 1 IP to get my 6.5 Suburban sorted out but now its super reliable.

I haven't checked the resistance on the glow plugs but I'm virtually certain everything else is workind and when the hard starting occurs the engine is warm enough that the glow plugs aren't called for. New batteries and starter is spinning fast. OPS is working and lift pump flow is confirmed. Water drain has been activated (that's the bleed valve on the front of the engine I believe). Air in lines is a possibility but why only when hot?

on mine, it turned out to be CRAPPY injectors.
I know the set under the turbo are a pain to get to, but pulling them, and popping them is a great idea. the GM injectors have a copper crush washer, not a heat shield like the MB's do...

John, you were getting hard hot starts with bad injectors? What about the big difference in starting between the two tanks of fuel? I can't think of any way to explain that besides a worn pump.

Our '97 Suburban 6.5 had a glow plug wire disconnected for a while. It didn't start differently with and without that glow plug but it doesn't get that cold here. No CEL or codes through the wait to start light.

Sixto
87 300D

You can spend the time to resistance check the injectors but it's much easier with test light to B+. I worked in truck country for 7 years, 5 in a GM dealer, and I've only seen a couple of glow plugs with wrong resistance that weren't completely open. And those showed up as a very dim test light.

I can head out now and start our 200k mile vans in 60deg weather without waiting for a full cycle of the GP's. I've seen newbie drivers hop into a van with a warm engine and turn the key right to start... and the van starts right up.

If you think the issue is due to a worn pump and fuel viscosity, you could try connecting a can containing four gals fuel mixed with a gallon of MMO to the fuel line. Start it cold, run it till warm, shut it down.

Here's a question: Is time a factor? IOW, if you shut the engine down hot then try a restart withing 10-15 seconds, will it start? Is the problem worse the longer you wait?

Did you check the lift pump output while hot? If the pump works cold but fails to work warm the IP may not be able to draw fuel through it. The IP can lift fuel a foot or so in most cases but don't count on it to happen.

Another no dollar test is to get the rear of the truck as high as possible. Air bubbles like to be at the top of a system and I would sometimes leave a hard start on the twin post lift with the rear axle raised to see if a hard start failed to occur.

Some guys like to add a check valve near the tank to prevent fuel drainback. It's not the right way to fix but it's good enough for some.

Any way to talk to PO about what he ran for fuel? I'm still betting he found an additive that helped and went with that instead of paying for a repair.

im putting my money on a worn injection pump after you test the glow plugs.

Sounds exactly like a school bus powered by a 6.5 I worked on a few years ago. Tough starts always, but once running, you could never say there was something wrong, just ran great after you finally managed to start it.

We tested all the glow plugs, replaced them all for good measure, tested all the injectors, and finally pulled and swapped the pump, which is really easy by the way on a 6.5.

That solved the problem, chances are your fuel lubricated injection pump has suffered a little from ULSD. When we pulled the old injection pump apart, it was full of galled surfaces and other worn areas.

I think it will start within a few seconds but much longer and it just cranks. Lift pump seems fine under all circumstances, at least it always shows pressure on the gauge. If it was an air leak problem, it seems it wouldn't start once it cools down either.
I should add that according to what I've read on numerous sites, problems with a hot start are typical of a worn IP. Here for instance:
Kennedy Diesel
The previous owner, by all appearances, was a stand up guy. I doubt he had tried any additives. He told me things that were wrong with the truck that would not have been evident otherwise.
One thing I don't like about this GMC is that there's no simple way to test the system with an alternate fuel supply. Metal lines in and out of the lift pump and the rubber line to the fuel filer very hard to access between the bell housing and the firewall.

Not sure what you mean by 'test light to B+'.

Have you tried adding 2 cycle oil to the fuel to supply extra lubrication for the IP?

I put a pint in both tanks when I filled up. Previous owner made no mention of using additives so it's easy to imagine that the ULSD took a toll on the pump.

I agree, the alternate fuel route is a pain. it is nice that the lift pump is right under the driver's door though.


I do agree, the injection pump is the primary suspect, but you knew that from the first post on here. I thought you were looking for alternatives to try before getting a pump.

I have a NA pump sitting on my shelf if you would like it to try...
I've also got a Ds4... if you feel like going electronic...

Where did you check the Lift Pump Pressure?
If I remember right there is a Diaphragm Type Lift Pump on the Engine (I think they had a Push Rod that would sometimes break) and I know for sure there is another Lift Pump inside of the IP.
The Lift Pump in the IP is the one responsible for creating the Pressure that charges the Head and Pistons.

When it is Hot can you Here the Shutoff Solenoid clicking? If a Shutoff Solenoid is bad it starts showing up when it is hot.

When I ran the DB2s on the Test Stand ran the Pump and checked that it had the Max Fuel and got the Pump nice and hot and then dropped down to cranking Speed to simulate hot starting.
If it did not pass that it was normally wear between the Head and the Rotor.

The other things than can effect it are there is an Air Bleed Fitting inside of the Pump that is supposed to allow X amount of Fuel through the Valve and X rpms. Near all of the Pumps I worked had too much return Fuel.
Another issue depending on if the advance Piston is Steel or not is the Aluminum Housing around the advance Piston wears and while the Advance is not anything at starting Fuel is going around the Piston.
Also wear on the Metering Valve cause excess return fuel.

I am adding this as a correction.

The Fuel Supply/Lift Pump in the sort of Nose Cone of the Fuel Injection Pump helps to control how much Fuel charges the Head and the Pistons.
If you look at the Nose Cone you see at 12:00 O'clock at the top of the Cone is a small Allen Head Bolt that has a serrated wedge of Metal on it that keeps the Nose Cone from rotating.
When you remove that Allen Bolt is where you tap in to check the Fuel Supply/Lift Pump. You need an adapter that screws into that tiny threaded Hole and you can connect your Fuel Pressure Gauge to that.

To change the pressure of the Fuel Supply/Lift Pump you remove the Fuel Inlet Fitting from the Nose Cone (depending on the ID of it) and you insert an extremely clean Allen Wrench into the center and inside there is an Allen Screw with a small Hole in it and turning it Clockwise increases the Pressure and opposite decreases the press.
Not that the small Hole in the Allen screw is easy to plug up.

Changing the Fuel Pressure there also can change the advance piston timing.

Note: The last time I rebuilt DB2 Fuel Injection Pumps was 1989.

In the pic the Red Arrow points to where the Port is to access the Lift Pump Pressure.
The Green arrow points to where you would be sticking the Allen Wrench in to adjust the Pressure.

I was wondering about that. I'm not sure how that system works and where the shut off solenoid is. I'm not hearing the clicking but I've never heard it so don't know exactly what to listen for.

That's true. I'm trying to exclude other possible causes. Do bad injectors cause hard hot starts? I found a supplier of rebuilt pumps with a new head at a pretty reasonable price. 6.5TD DB2-4911 Manual Injection Pump :: SSDiesel Supply :: GM 6.5 TD Specialists

Local shop where ForcedInduction uses to work wanted $2200 for a rebuilt pump + $540 to install.

Kerry: The solenoid is attached to the IP. It's under a "cover" on the top of the pump. You could use a screwdriver or stethoscope touching the cover to listen for clicking.
http://www.motormayhem.net/wp-upload...GE0038.JPG.jpg

Test light to B+ means one end of your test light is connected to the battery positive lead. When you touch the glow plug electrical connection point you're looking for a path to ground.

While these suggestions are all designed to help troubleshoot, I also believe you'll be needing a pump. Diesel911's information helps you test the pump instead of diagnosing by elimination. Here's a page with more information than the typical service manual: » Stanadyne DB2 Fuel Injection Pump &raquo Motor Mayhem

I have a 5/8" 5 point crow's foot here which is a great help when disconnecting fuel lines from the IP.
http://thumbs4.ebaystatic.com/d/l225...BP67zQfviA.jpg

That picture of the solenoid is helpful. From what I read, the standard test for a worn pump is the cold water test--when failing to start when hot, pour cold water on the IP. If it starts, it's a bad pump. but I wondered if the cold water might also stimulate a stuck shut off solenoid to release.

If the truck sat for a while, it could be a deposit from old fuel. I had a bad sticking rack issue on a Detroit from old fuel, it ran fine until I took it up to operating temp then the rack stuck the next time I ran it. The excess fuel from that machine did make my 7.3 with a DB2 pump run a bit funny for a while but mixing a quart of Dexron with each tank for a few tanks cleared that up.
The ATF might work in your truck as well, if not try some Diesel Kleen or even run a couple cans of purge through it.

It is the other way around.
When Solenoid does not work the Spring keeps the Lever in the shutoff Position. When you turn the Key on to start or run the Solenoid gets voltage and that Lever is pulled back and held there until the Voltage is cut off.

Scribe a line on both Sides of the Cover so it goes back in Exactly the same place.

The only Field Test I know that can be done is to remove the Cover. However, I have no idea what also might be on that Year and Model of Cover.
If you remove the Cover and the Engine Starts Hot like that it very likely the shutoff Solenoid.

(I can not remember if the Cover has tamper proof Screws or not?)

While putting the cover back on is not hard it is possible to mess that up. If you look at that pic 1project2many posted you can see how the Solenoid Lever goes to the left of the Metering Valve Lever (Black).
What that means is that when the Pump is on the Engine the with you standing in front of the Vehicle facing the Fire Wall; you would install the cover with it partly overhanging to the rear of the Pump (towards the Radiator) and slide if forward so it catches on the Metering Valve.
You will feel a slight amount of spring tension when you do that.
All of the Cover Screw parts need to go back to where they were.

You won't want to run it long as the Governor is going to throw a lot of Fuel out of the Pump.

Putting the IP top Cover on wrong may cause the Engine to Run away.

The below pic is a generic one. Your top cover is likely different. Some setups have a Flat Metal ground Strap, so ground directly to the Cover with washers.

I have some additional thoughts. My starter seems to be drawing a lot of power. Too much power since it's drawing down the dual batteries very quickly when it fails to start. The batteries were new last week and I'm not getting 30 seconds of cranking out of them before the engine is slowing waaay down. I've load checked the batteries and they test fine. I'm wondering if it's drawing enough power to reduce the voltage at the fuel shut off solenoid enough so that it's not activating.

This is supposed to be how the IP works.

Stanadyne DB2 Injection Pump - Diesel Engine - Diesel Power Magazine

Time for a new IP. Hard starting when hot is common when the IP seals are no good. DB2 pumps don't last near as long as the Bosch style pumps.

Yes, I agree that is their reputation but I'm still puzzled by the rapid onset. No problems one day to constant hot no-starts a few days later with no other symptoms. Other people have suggested that a worn pump also smokes and it was squeaky clean at the emissions test 3 weeks ago.

This guy claims a bad throttle position sensor can cause a no-start condition. Anyone ever hear of that?

Trouble Shooting Challenge NO Start Mechanical Injection - Diesel Place : Chevrolet and GMC Diesel Truck Forums

Uh, I don't think so...

Thinner fuel will seep past seals easier than thicker fuel. Perhaps the winter blend is just thin enough to seep too much. You could add some new engine oil or ATF and see if that helps thicken the fuel enough. You have dead-on symptoms of a worn IP, though.

Here's an update on the situation. I replaced the starter and the problem appears to have gone away. I replaced the starter because the last time I tried to start it hot it groaned, barely turned the engine over but the batteries load tested fine. The new starter definitely spins the engine faster. I've tried warmly the engine up, letting it heat soak for 15 minutes and restarted it. It's started up right away each of the 5 times I tried it. I haven't taken it on a hard hot drive yet to test it but it appears the problem may have been the starter all along. I couldn't notice any difference in starting rpm's hot or cold on the old starter. I can't account for the fact that it fired up with the old starter after putting cold water on the IP. That worked 3 times. But if this new starter has indeed solved the problem it points to the fact that perhaps water on the IP is not definitive proof of a worn out IP.

Hmm

so when you said "harder to start" you meant the motor didn't turn as fast when hot?
I assumed the crank speed was unaffected by the motor temp, but the motor would not fire.

replacing the battery/starter harness with welding cable and tinned crimped ends is a standard upgrade to these motors (as is replacing the oil cooler line fittings!!!) you changing the starter, which required disconnecting the batteries, could have cleaned up the connections enough to eliminate the problem too...

No, the engine turned at the same speed hot or cold (until the last two attempts prior to starter replacement). At least I could not detect by ear any difference in the cranking speed. It just didn't fire. It did fire after I poured the water on the IP.
Except for the connections to the solenoid, all battery connections had been cleaned a week prior when I replaced the batteries. I had noticed a slightly slower starter speed on a cold morning and the batteries were 7 yrs old.

So it's a mystery to me as to how a new starter solved the problem when the water on the IP had got it to fire.

well... it's slightly cooler outside now than it was when you started this thread... perhaps the IP is just REALLY sensitive to fuel temp?

Perhaps. It is about 15 degrees cooler today but Sunday it was just about the same temperature it was when it was not starting last Monday.

Interesting! Glad I came back to take a look at this thread.

If water being poured on the IP made it start then there is a 90% chance it is a worn IP, (average service life is said to be around 100k for these pumps as well). It is sort of a universal sign in db2 whether it is ford gm or whatever.