Ok, I think this bears a thread of it's own now. This has been kicking my butt for some time.

My '94 Suburban has to work hard to start cold. It chugs for about 10-15 seconds before starting and will die immediately unless you give it about 1/4 throttle. After a couple seconds it "settles down" it runs and idles fine.
It has also been completely unwilling to start after shutting down at operating tempurature and then sitting for 20 minutes or so. If I crack an injector, it weeps fuel, but doesn't start. It will start fine after the engine cools down completely. A recent trick I learned (thanks Scrufdog!) of unhooking the coolant temp sensor seems to work, and the engine will start after 10 seconds or so of chugging, similar to normal cold starts.

Here are the recent mainenance items done:

1- Installed new PMD on firewall mounted heat-sink. (fixed previous stalling issue)
2- replaced Injectors and glow plugs. (didn't troubleshoot a problem with them, but figured it was due at 220K miles) Good voltage on all glow plugs verified.
3- Changed lift pump wire routing so that lift pump is powered by ignition circuit. (attempt to pre-charge injector pump and allow easier lift pump troubleshooting) ((yes, I have read the vehement threads on this topic, I'll probably switch it to a diode arrangement soon))
4- Temporily installed clear fuel line in place of injector fuel return lines. Consistent bubble stream at several injectors lead me to believe that I had a vacuum seal issue upstream of the lift pump.
5- Removed everything from the lift pump aft. Cleaned, resealed and vacuum tested the lift pump, fuel lines, and fuel pickup/sender unit. Reassembled all.

After all that, I'm still showing bubbles in the fuel return lines. In fact, if anything, they are worse. I suppose that they are contributing to the hot start issue. Tomorrow, I will try to swap in an old injector to see if the bubbling stops. Beyond that, over to the peanut gallery for ideas at this point. I'm also curious as to the reason why the engine will start hot if I unplug the coolant sensor.

Carnie. I have the same problem. I'm good for one start a day. I am installing a new ECT sensor tomorrow with my fingers crossed.

I have a '92 6.5 turbo, a little different injection system, but somtimes it wouldn't start hot, and somtimes it would. Seems like when it wouldn't the glow plug light wouldn't come on. My plugs come on somtimes when its at operating temp. Replaced the batteries and its been fine ever since, any idea how old your batteries are? Might be worth a shot unless your sure is a fuel issue.

Ah yes, add to the recent maintenance list:
6- Installed 2 new batties, Thoroghly cleaned connections and grounds.
7- Changed fuel filter (twice) just in case.

I can absolutely see the air bubble percolating in the temporary clear fuel return lines. I'm no rocket scientist, but I'm pretty sure those bubbles aren't supposed to be there.
markarnold, I'm curious to know how your ECT sesor works out. Let me know. And try that unplugging the coolant temp sensor trick. Its the one front and center on a 6.5L, on the aluminum housing attached to the radiator inlet hose. It's a two prong cannon plug with one black and one yellow wire.

HRC, you've got the ole DB2 pump. Faithful pump, until you get the no-hot-start issue. Indiciator of internal pump wear between head and rotor. Replacement may be looming on the horizon. You can limp along with longer glow time.

Carnie, the bubbles in the return or supply line to the pump? If you have solid column of liquid fuel TO the pump, then fuel doesn't seem to be the problem. You may have a rare DS4 head rotor issue maybe.... Maybe one of the pump guys could steer you on that one.

The temporary clear lines are replacing the fuel return lines between the injectors for the purpose of seeing if bubbles are coming out of the injectors. They are. I am seeing small bubbles (1/32" or smaller) coming out of several injectors at a lazy rate that doesn't seem to diminish over time. This leads me to believe that the injectors themselves are not the problem, besides I replaced them all last November. Tomorrow I will pull the fuel filter again and carefully check for seal integrity, although I would expect a leak at the filter housing would be pushing fuel out, not sucking air in.

I actually have a used IP from a '96 6.5L sitting in a box that I bought to strip the PMD. However, I am loath to swap the IP unless I am SURE that is the root of the problem.

So does anyone else have ideas that are troubleshootable? No idea to silly.

That's a solenoid-type lift pump - can buzz without pumping - the purpose of the lift-pump test is to eliminate it as causative.

Post the DS4-xxx-xxxx number off the '96 spare.

The lift pump pumps like a champ, and after all my troubleshooting I am confident that I have eliminated the the lift pump or anything behind it as a source of my problems.

The numbers on the spare IP are:
Stanadyne E6 DS4831 S5288 J
Mod 8549602
S/N? 12558156

I think I recall the guy who sold it saying it came off a '96 with 90K, but I could be off on the details.

That's a 5288 - probably a 5521 on your engine.

Try using clear hose on the IP return, see if the problem starts there - bubbles indicate whatever is pumping to the IP is not keeping up with IP demand.

OK, so if I see bubbles in the IP return what does that tell me different from bubbles in the injector return lines?

If I can't resolve the bubble issue between the filter housing and the injectors, I assume I'm going to need to swap IPs.
Is there any issue with swapping the spare IP that I listed into a '94?

Carnie There is a solenoid on the lift pump designed to shut off fuel for a number of reasons. I have a training manual for the 6.5. It says that if there is anything wrong with the circuit for the IP shut off solenoid then the truck will not start. send your email address and I will send the PDF manuel

Sure.. it's
michael.murphree@verizon.net

1. Does the engine Turn over? Yes
1a. Does the engine start? Yes, but starts hard with eng Cold, 10-20 seconds on chugging.
Will not hot start (engine hot) after 10-20 minutes of sitting, unless I pull the ECT plug. Then it starts like a cold start.
1b. Do you have a Wait To Start Light & duration lit. Yes, 6 sec hot 10 sec cold.
1c. Ambient Condition (temperature outside) 60-80 deg F
1d. Engine Cranking speed (if you have an accurate tachometer). No Tach, but cranks fast.
1e. Are you experiencing stalling? Only immediately after start. Mitigated by giving ~1/2 throttle.
1f. If Stalling, describe (upon startup only, down the road, hit a bump etc)
1g. If Stalling, do you notice loss of dash or instruments?
1.1Lift pump test (http://dieselplace.com/forum/showthread.php?t=39350)- describe results. 7 psi at the T-valve with good flow both at idle and during cranking.
2.Service Engine Light - on/off/intermittent. OFF
3.Model year '94
3a. Odometer reading 220K
3b. Miles on major engine components if been replaced (example Injection pump) Unknown. IP is blue data tag DS-S5459
4.Do you have any engine codes? (don't assume no SES light, no codes either) Yes or No. NO
5.If you do have engine codes - what are they?
6.Air Filter condition (visual check) GOOD
7.Fuel filter condition (freshly changed or condition unknown) FRESH CHANGE, old one looked clean too.
8.Condition of Battery terminal connections (removed, cleaned and tightened) RECENTLY removed, cleaned, tightened.
8A.Known condition and age of the batteries. 2 Years, good condition
8B.Are batteries of differing age or are they a matched set? Matched
9.Upon cold start, does the radiator hose get hard quickly? Yes/no NO
10.Upon cold start, do you have excessive white smoke? Yes/no NO
11.Do you have excessive cranking time before the engine starts? YES
12.Have you used the block heater, and does this effect engine starting? NO
13.During hard acceleration, do you have excessive black smoke? Yes/no NO
14.Do you have any unusual exhaust smoke issues? NO
15.Turbo check out (http://dieselplace.com/forum/showthread.php?t=39368)- pass/fail PASS typical 5lb boost max
16.Do you have an EGR on the engine? (An F or an S engine code) F code
17.Indicate if you know if it’s a 1500, 2500, 2500HD, 3500, 3500HD. 2500
18.Indicate fuel that you are using: Bio-diesel, #2 Diesel, #1Diesel, SVO/WVO, other
18a. If running a VO setup, indicate details of your conversion (homemade, or packaged system)
19.Are you using any fuel additives? If so, please list. PS
20.Please indicate geographic region you are in: (example: Texas or Canada) High desert, California
21.Do you have any service history available that might pertain to the problem you are having? See below
22.Please indicate any modifications to the vehicle that might help us diagnose better. Extra Lift Pump relay wired to ignition circuit. (yes, I know this is supposed to be bad)
23.Upon unscrewing the fuel cap (http://dieselplace.com/forum/showthread.php?t=42338), do you have a large vacuum formed in the tank? yes/no NO, plus new diesel cap
24.Location of PMD/FSD (http://www.dieselplace.com/forum/showthread.php?t=39436)? On the pump/remoted over intake/remoted out of engine bay (please specify specifically) On homemade heat sink drivers side firewall mount. PMD replaced 4 months ago.
25.Are ALL glow plugs in proper working order as per this thread (http://www.dieselplace.com/forum/showthread.php?t=39182)? Yes, plus all new last 4 months 60G.

More recent maintenance and troubleshooting efforts:
-All new bosch injectors 1K miles ago.
-Removed entire fuel supply system from lift pump aft. Cleaned, lubed, inspected, and replaced o-rings for fuel pickup/sender unit and hard lines.
-Vacuum tested hard lines. check good
-assembled fuel pickup, hard lines and lift pump in garage with pickup in bucket 'o fuel. Installed clear line on lift pump and jumped it. Fuel ran clear out of lift pump with no bubbles. Reinstall all.
-Swapped lift pump with my '99 Burb, just in case. Still makes 7 psi.
-installed clear fuel hoses (temporary) to troubleshoot bubbles in fuel system. Results:

#7-5-3-1 injector. small bubbles, 1/32" or so, slow, lazy rate
#1 injector-fuel return manifold. small bubbles, 1/32", slow rate
#6-8 injector small bubbles, 1/32", slow rate
#2-return manifold. Varies, slow bubbles on startup, as engine warms bubbles bocome faster. At op temp large bubbles at a fast rate. Bubbles continue for several seconds after shutdown.
Filter housing-IP inlet. No bubbles
IP outlet-return manifold. No bubbles
return manifold-return line. Varies with the #2-return manifold rate.

So at this point I have eliminated everything from the tank to the IP inlet at the source of the air bubbles.
The bubbles are most severe coming from the #2 injector return, though I don't know about the output of #4 and #6 injector.

Could this be a leaking injector on the Passenger side? (of course:mad: )
Or is this more indicative of the IP itself?

Since #2 feed is from all 4 injectors on the even side, you can swap each one with it's driver-side mate to determine the source.

Well, I have been trying very hard for the last month or so NOT to come to this conclusion, but here it is:

My IP is the problem.

I have spent the last week with clear hose on all the fuel return lines, watching bubbles from this injector or that injector. I have swapped known "good" injectors that didn't make bubbles into the positions of suspected "bad" injectors. Several times in some cases. Here is what I have observed:

-There are no bubbles in any of the fuel supply lines, or in the IP return line.
-The #2 and #3 injectors bubble significantly no matter what injector is put in that position.

I have some rudimentary instructions for swapping IPs from an electronic Chilton manual, but I wanted to poll the audience before swapping them.

-The IP currently on the '94 Burb is a "DS-S5459" model with blue data plate and green tag. Milage on pump unknown.
-The IP I have in a box is a "E6 DS4831-S5288 J" model with a blue data plate and green tag. Claimed to have come off a '96 truck with 90K miles and blown engine.
-Does it make sense to swap these IPs?
-How hard is it to swap IPs?
-Are there any special tools that are required or would greatly help in doing the job?
-Will a computer swap be required if I swap these IPs?
-I don't have any electroninc gear to adjust timing after a swap. Will timing adjustment be required? How much does it typically cost to have that done?

Direct interchange, IP and PCM - if you carefully mark the 5459 IP\timing cover, pull the IP, carefully transcribe the mark over to the 5288, carefully install it to the timing cover, it should be within a RCH of the original timing.

Swedeburb's GMTDScanTech is inexpensive, will do anything Tech2 can do.

Didn't go back thru all the machinations, so - have you tried it without the OPS Filter, or replaced the Crank Position Sensor?

I take it that means my PCM is compatable with the 5288.

The OPS is bypassed for lift pump operation, so shouldn't be a factor. Besides, solid 7psi from lift pump at all paramenters.
I have not replaced the Crank Position Sensor. Could that be a factor in a bubbling IP? (can I rob it off the spare IP?)

Someone had a Stanadyne DS4 parts diagram on here before, but the link is now expired. Anyone have an updated parts diagram link?

My bad - that's OS filter, rectabular rubber piece, 6-wires, between the engine harness and the OS connector - remove it, connect the OS direct to the engine harness.

If that's the original black-label IP it prolly is time for an upgrade.

There is no OS filter that I could find when I had the intake plenum off.
The IP is a blue label green tag listed above.

The essential question is: If we assume that the injectors are good, and there is no fuel supply issue to the IP, is there anything else that would make the IP start producing bubbles other that some internal failure requireing IP replacement?

Ok, some '94-95 need the OS filter to run, some don't - you might try installing one, see if that clears things up - several vendors carry them.

You're right, that IP looks good on the return line, but at 1-8-7-2-6-5-4-3, #2 and #3 are not even consecutive on the distributor - acts sorta like the pipes are crossed, tho, with those bubbles on 2 and 3.

How 'bout compression?

Well, wait - 2 and 3 are diametrically opposite on the distributor, which means they use the same ramps, so if the ramps were damaged, the injection event would be identical for both cyls.

Be handy if you could get it on a scanner, watch cyl balance at idle

What is interesting here, is the length of time to crank. No hot start, sounds odd, with a long cold crank too - no codes? OBD-I setup - are you getting a code 12? Making sure that we are not ironing out maybe a missing electronic link to the puzzle here too. Like a blown out service engine light.

As far as parts for the DS4, that tends to be a bit hush hush. Almost all parts need to be done on the very expensive pump stand at a fuel shop. You can change the optical sensor, fuel shut off solenoid and the stepper motor, but that tends to be the length of the list.

There are some posts on here about changing and doing other things to the fuel solenoid listed on here, but opinions there are not necessarily endorsed by the staff or management of this station.