I have a Sub that is giving me trouble, It cranks fine but stumbles to a start hot or cold. Sometimes worse than others a few trys at it, But it does start. It has a new GM pump, Sets no codes, Good lift pump, No air in the lines, Complete fuel supply system checked and cleaned, Good compression, Good glow plug sys.
I am getting to my wits end, There is not much left that can cause such a thing. It has 147,000 a full set of injectors were installed 70,000 miles ago according to the warranty history, and this will be its second pump. Thanks for any suggestions anyone can give.

Rob

If the fuel system has been checked out, lift pump, OPS, bled air. I would check and clean your battery terminals especially the positive on the passenger side, the one that is stacked up with 2 leads. Those side terminals can look clean but be filled with the chalky green inside. Dude at Autozone tried to tell me my starter was bad a couple years back when I was having starting probs and I suspected their warrantied batteries. I cleaned the crud and keep them coated in that red oil stuff now days.

Check the Stanadyne label - which DS4 Inj Pump was installed?

Its a DS4831-5521 pump. and the battery's are not the problem, cranking speed is good, It cranks fine just stumbles as it trys to start then eventually catches.

Thanks
Rob

Excellent - seems as tho an OBDII 5521 Inj Pump installed in an OBDI system usually results in difficult-starting symptoms, based on an unofficial, informal, informed study.

May have to do with lift pump operation dissimilarities.

OBDI operates at START, then OPS control.

OBDII operates at IGN on, is PCM controlled with OPS control.

OBDII is pressurizing during WAIT TO START glow event - OBDI is not...............

'94-'95 is OBDI, '96-up is OBDII.

5521 possibly requires pre-pressurization afforded by OBDII, as my OBDI engine will start within 1/2 crank revolution, if re-cranked within a few minutes of warm shut-down.

My engine always started within 1/2 crank rev with the 5288 Inj Pump which is now in QM's engine - even at winter starting.

Now, with new 5521, takes 2 to 3, sometimes more, full crank revolutions to start.
Very embarrassing, to an ole gear-head, to whom was often commented 'do ya just leave yer truck runnin'? Ah don' never even hear ya even crank 'at sucker!'

Workin' on a possible solution, even as we type...............:cool:

OPS by-pass with add-a-circuit powered with ignition in place of fuel pump solenoid?

$7 for the add-a-circuit. Wouldn't cost too much to try, but may have to unplug OPS while the add-a-circuit is installed. If you find it starts better, simply cut the gray wire to OPS and reconnect to get your oil pressure gage back. Thats how I run mine all the time.

I prefer the pressurized Diesel Fuel supply system in my truck safely shuts off when engine loses oil pressure, as designed.

Might not have sufficient motor-nerve skills available to turn Ign switch off, in all circumstances.

There are several safer simpler methods - just need be tested for intrinsic safety, as required by a vehicle designed for possible occupation by family members.

In other safety-defeating scenarios, wire the OPS to control the auxiliary relay that switches the voltage to the lift pump - relay coil is low-current load, won't burn contacts, if commutated.

Or, just replace OPS about every 5 years - hot engine oil is gonna eventually make it leak, anyway.

Point taken. I know it's not the safest way to do things, so I try that much harder not to get into an accident.;)

But I can't imagine an easier way to check if fuel pressure with turn of key would help startability. Unplug relay, plug in add-a-circuit, unplug OPS. Done. See how she starts. If it doesn't do any good, in five minutes you remove add-a-circuit, plug in the fuel pump relay, and plug in OPS, and your back where you started from.

On my '94 OBDI blazer you can power the lift pump by appling 12v to the bottom left pin on the ALDL plug. I use this to bleed air when I replace the fuel filter. I've never started the truck while it is powered this way because because I don't know if doing so would backfeed anything wrong. You know I don't want to do anything to screw that circuit up anymore than it already is, but if you wired a momentary switch this way you could pre-pressureize the IP housing then let off and crank it or just jump it temp. style to see if it makes a difference with your starting issue.

You're doing the same thing the Start Relay and the OPS does, lupey - applying +12v power to the lift pump.

Won't say that can't hurt it, because nothing is idiot proof, but TechX tools use that OBDI ALDL pin as test verification, to drive the lift pump, and also to check for normally-applied voltage to the lift pump.

JD's right about that pump, when all's in order it takes a 1/2 crank to start the engine. How old are your injectors?

First - assuming the problem is fresh, not several months old - start the engine, run it at 2000rpm for about 15mins to clear any recalcitrant bubbles outta the IP\injector pipes system.
Make sure you got 15mins at 2000rpm fuel in the tank.

This would work better in limp mode, so PCM won't be constantly correcting, but give it a try, ennyhoo.

Shut it off, wait about a minute, then re-crank it, then post results.

His '94 model won't automatically relearn TDC offset like OBDIIs will, maybe it never got set right...

Are you sure its a NEW pump? Not that they're any better than remans....

I do know one thing about it - Pulse Width runs ~1.95ms on these 5521 IP's, whether oem in '98-up OBDII's, or replacement IP in OBDI.
The 5288 ran 1.88ms, as baseline, falling into the 1.70's at 3000rpm, same as 5521.

And all the OBDI's get long crank, difficult start with the 5521.

Well - that's two er three things...........

Let's go fer more - once't my engine is runnin', it is smooth and powerful - don't lope, miss, stumble, fishbite, and cranks immediately, if restarted soon after shutdown.

Well - now I'm losin' count of things I know about it.........

What do you think about it, TDG, since't you work on'em, daily?

Not even to exclude DieselPro, who's lost his dash........

Oh, yeah- if his TDC Offset was that fur off, it'd set DTC, don'tcha think?

got exactly the same symptoms. 94 obdI with 5521 ( #7 :() last fall.
cold cranking take awhile. starter, batteries, LP pressure, OPS, compression, etc are all strong/recently replaced.
1/2 crank to start right after shutdown.
i first noticed this right after an IP replacement a couple years ago.
my injectors are nearing end of life ( 130kms, or 81K miles ).
truck runs strong. pump is set at -1.5. no stumbles, misses. just this darn extended crank start.

there has to be a relay mod that won't affect safety. how about off the glow cycle? could i add-a-circuit to the glow fuse & trip a relay that ties 12V back in behind the fuel relay? or would a momentary switch be better?

Haven't tested either option, yet, but -

remove START wire to Lift Pump Start relay, add to Glow Relay - runs in Glow, not in START, but Inj Pump should be primed by then for 1/2rev start.

Or - (cool play on words, here, don'tcha think?) diode-or START and GLOW to Lift Pump Relay coil, lift pump runs at both events, OPS takes over when engine starts.

Need two 1a diodes, one for GLOW, One for START - Radshak got'em cheap.

What if you track down the lead to the wait to start light and jumped or relayed that to a single diode spliced in behind the ALDL. That would keep the wait light from staying on when the lift pump is running at start and when the OPS takes over.

Easier done in engine compartment, where WAIT TO START signal comes from, wouldn'tcha think?

Wondering about the extended silence from the two pump guys..........................

Pull a glow plug and plug the lead back in, then cycle them. I bet you'll find the glows are getting redhot.

I do know one thing about it - Pulse Width runs ~1.95ms on these 5521 IP's, whether oem in '98-up OBDII's, or replacement IP in OBDI.
And all the OBDI's get long crank, difficult start with the 5521.

I think I have pitched in about this as well. I've seen a lot of guys who just left the dealership with brand new pump in, and want us to scan it and check the timing/what not. Don't ask my why the dealership isn't capable of that but they certainly aren't! Atleast they don't deny it ;)
Anyway, a lot of the same complaints with new pump, long 1.8+ CTIMES, extended crank, well not really extended but longer than what their trucks 'used to start like'.
I'm telling you, its the LONG CLOSURE times that cause it. If you ever get a chance, watch CTIME with a new pump on cold start, often, you will see 2.4+ times! Late start of injection (timing) and lost fuel delivery quantity. I've also noticed, ONLY in '02+ 5521 cores, that the face of the fuel solenoid which pulls the armature towards itself to close, has a pretty rough finish, not from wear, from MFGing, also, occassionally see taller shims under the poppet valve spring. Lap the solenoid face, adjust shims if necessary, and ALL of my pumps leave the shop with a CTIME in the 1.55-1.75 range. Its their nature to drop a little when running diesel fuel instead of calibration fluid, sometimes almost a tenth, depending on fuel quality, so I keep them on the low side. Setting return oil to high end of spec clears air fast on initial startup, if these pumps get into the right hands, Startability can be improved over where they were new from Stanadyne.

Diesel Pro, chime in brother, surely you've noticed some of the same?

Not to mention, we've even recieved some NEW DS pumps from dealers that complained of either no start/hard start/very low power, and Test As Recieved revealed that the optic sensor setting was way off, recalibrated, sent them back and haven't heard a peep about them.

I do not disagree, as such, but - the late OBDII's crank and run well with the 5521 and ~1.95ms pulse.
And mine instantly cranks shortly after shutdown, mostly in operating temp conditions, but has done so at cold shut-down, restart.

A considerable number of OBDI\5521 complaints have aired on these several forums.
The normal-starting when residual fuel pressure is up sorta points to one problem.

Residual fuel pressure is dependent on the two one-way valves in the lift pump, which seal much better with inertial velocity - 'nother words, they gotta be runnin' to do the seal-thang, well.

Which would also mean difficult starts with older lift pump.

Mine is new.

Add to that, GM changed lift pump operation for '96 OBDII release.

Add to that, '99 was to see the 215hp upgrade, approximately at exactly the same time the 5521 was released, maybe.

Mebbe they jus' want these ole OBDI's to disappear, as Timeset and TDCO are more transparent - even to the untrained\unskilled, like moi - making it easier to defeat smog-cops limitations.

So - OBDII runs well, OBDI runs well
OBDII cranks well, OBDI don't crank so well, mostly.

Both, with 1.95ms pw.

Whaddya think?

OBDII trucks have a 'better' start up, cold warm up, and higher HP output because of programming changes. None of the mechanical updates in the 5521 have any effect on the pumps performance, they're more addressed to longevity, and cutting production costs. Calibration setting and checks are identical, except for one of the runs used to determine resistor value, but thats a negligible difference.
It only takes less a 1/4 turn of the IP (1/2 engine), even with no supply pressure, to get transfer pressure high enough to fill the plungers and start pumping fuel, assuming the transfer pump is fully operable.

BTW - hard\difficult start is relatively subjective.

I consider anything over 1/2 crank rev as difficult, with 5revs getting into the hard-start area.

ronniejoe - '95 OBDI with 5521 - indicated he thought 2 to 5 revs as easy start.

Two revs to run is embarrasing - over 5, and I feel like paintin' it green, and hidin' it in the tall grass......knowwhutImean, Vern?

Even with the engine in mine being in as questionable shape as it is, and being an OBDI with 5521 IP, with a warm engine you can barely get off the starter fast enough. I'm positive, overall startability is determined by the pump.
Supply pressure, fuel quality, injectors, compression, Glowplug system, starter speed are all factors, and if you don't have any one of those at near 100% you probably won't get quick starting, but you can have all of those things and a 'weak' IP that can cause slow starts too.

What about anti leak-back valving? Any difference in pressure input threshold?
Housing pressure, bypass? Return-line pressure?

Anything that would be effected during shut-down?

It runs well - tremendous power with 83mm3 fuel rate and 20psi Boost, 8.5deg D\A,
-1.50deg TDCO.
I tried the -1.94deg TDCO, but it sounded like the pre-cups were being violently shattered, so I adj it back to -1.50deg

BTW - that ball pein hammer sound of the 6.2\6.5 is the pre-cups violently expanding against the walls of their little cubby holes.

Real scary on a 40deg winter morn, with -1.94deg TDCO........

I would like to get back the 1/2 turn- to-run starting event.

Are you talking about supply pressure, transfer pressure or high pressure lines to the injectors? There are anti leakback mechanisms inplace for all of these, either for that purpose of simply by the nature of the design. But none of them will hold pressure for more than a few seconds, as that is more than is needed during operation.

Housing pressure will drop immediately, less than 5lbs at cranking even with high end return oil, mine and several trucks I've done I notice when the return hose is unplugged from the pump you can hear the fuel rush to the tank, indicating there is a slight vacuum created from fuel falling to the lower level in the tank.

Again, OBDI/OBDII even 96-97 compared to 98+ sound different on cold start/run because of differences in programming.

[QUOTE=gmctd]
BTW - that ball pein hammer sound of the 6.2\6.5 is the pre-cups violently expanding against the walls of their little cubby holes.
QUOTE]

My dremel work seems to have reducd the cup noise. The Rut rut rut has become a tuh tuh tuh, noticably muted.

Advance and cold will bring it back, believe me.........

I broke my fast idle set getting the linkage right, so when I went out and started it, It cought immediatly and idled at 600 RPM, no fast idle advance but the loud rut rut was quite absent.

Cold-cold-cold-cold - meaning, try it at 40deg ambient..........

Mine, lift pump rewired as OBDII compliant, starts within 1/2 crank revolution, again.

And, considerably quieter than yesterday's 45deg o'nite ambient

Hey you "southeners" have aver heard one starting at -20 ???

I am glad I live in the country, after all the blue smoke clears the valley, motor still sounds like pistons are coming out...bottom or top.....

And I can guarantee it takes more than 1/2 revolution or 2 to 5 to start it even plugged in.

I usually let it warm up for 30 to 45 minutes before moving it, and this winter I let it run all night when we had a -45

On the positive side, it's almost like having a natural Intercooler.....:D

I plug mine in below 32*F or 0*C, So I plugged it in about three nights this year. Hey val, It's already A/C weather here and all the flowers and trees are budding out.

QM I used to like your posts, I think I am changing my mind....;)

:Nothing_f we are going to get into the 40s today...HA ! Time to get short sleeves out.

Mine, lift pump rewired as OBDII compliant, starts within 1/2 crank revolution, again.


You mentioned a couple options in an earlier post. I'd like to try what you did.
Any detailed foolproof instructions for would be most appreciated by this noob.:) thx!

What is required is for the lift pump to run in WAIT TO START, then continue running in START, where the OPS will take over as oil pressure increases with engine running.

What you'll be doing is connecting the two circuits together, such that neither circuit back-feeds the other - meaning WAIT TO START will not crank starter, and START will not GLOW, yet the lift pump will do it's thing at both events.

What you'll need is two @ 50volt 1 amp mimimum epoxy RECTIFIER diodes from Radshak - 1N4001, 1N4002, etc.
2amp or 3amp diodes - 1N5406 equiv - are more suitable.
Each epoxy diode will have a white band around one end.

What you will do is cut the purple\white lift pump wire from the 5a CRK (crank) fuse, splice in a rectifier diode to the short purple\white wire you left on the fuse-holder, and splice a second diode from the purple\white lift pump wire to the dark blue wire from the Glow Plug fuse-holder.

What needs to be done is connect the banded-end lead-wire on each diode to the purple lift pump wire.
Lead-wire at opposite end of one diode will connect to the CRK fuse, lead-wire at opposite end of second diode will connect to the Glow fuse.

What will happen is +12volts on either diode will energize the Lift Pump Relay, which applies pre-run power to the lift pump motor - the other diode blocks +12v from it's circuit.

What you should notice, all other things being equal, is easier starting.

What do you think - of that?

What? me worry? :cool:

cool, I'd like to do this ,too.

It is now public offering, compliments of "nobody"............:cool:

An' don' fergit - ya sawr it here, on the DP, 1rst.

)sorta like mailin' yerse'f a letter, ta git the postmarked date and time, rite?(

This thread has sparked something that has been in the back of my mind. When you shut down these trucks the lift pump still runs until the oil pressure drops off. So- if you installed a pre-oiler not only would you get fresh oil flowing through the block and turbo but it would also run the lift pump via the OPS.

Thats something new, I think that would work Lupey, be good for the engine/turbo anyway.

Good idea, lupey - could combine it with an oil pan heater to flow preheated oil thru the system for winter climes..............:cool:

ok, i made an attempt to get at the wiring behind the fuse panel ( mine is lower left dash just above the hood release), but there's just no room to work up under there, let alone solder a wire. i was hoping i could back out the fuse panel and just let it hang while i installed the diodes, but the wiring harness just isnt long enough...or i don't have the Censored patience .
i dont have a wiring diagram... is there an easier way to get at those wires from under the hood instead? i thought i saw a purple/white wire going into the fuel relay on the firewall near the 12V accessory panel. is it the samewire? what if i add a circuit to each of the glow & crank fuses on the front of the fuse panel, solder in the diodes , join them and run a lead thru the firewall to the purple/white going into the fuel relay? same same?

Samo samo no sweat, GI................

Or - splice the two diodes directly into the wire you will cut at the relay, band goes to the wire to the relay, other end of one diode goes to the wire back into the harness.

Other end of the other diode ties to the orange wire on the large terminal on the Glow Plug Relay, pin A - don't cut this wire, just connect the diode to it.

For safety, use an inline fuseholder and a 1amp fuse between each diode and it's respective circuit.

So, two diodes, two fuseholders, and two 1amp fuses to get it done in the engine bay.

Stike that pink\black wire connection, steve - should be the orange wire from the large terminal on the glow plug relay.

The pink\black wire is hot at power-on, won't release lift pump control to OPS.

I've changed it in the other post, also.......sorry 'bout that:o:

gmctd, many thanks.
got the mod installed under the hood. LP starts pumping as soon as the glow cycle starts, and the start is definitely improved.
learned a couple things - when tightening down the lead nuts on top of the glow relay, well, make sure you've got a wrench on the bottom nut cuz if you don't, and you tighten too far, it breaks the copper post right out of the plastic relay housing :badidea:. didnt have a wrench thin enough to fit so i tried without...so now i have a 13mm open end wrench with the thickness ground down about 1/16 as that lower nut is thinner....and a new glow relay!

also, the only epoxy rectifier diode Radio shack locally had was a 3amp, so thats what i used. but then i only had a 1.5amp inline fuse so i tried it. didnt last long. so now I have a sleeve of 3 amp fuses. seems to be ok.

wire leads, connectors, fuse and diodes are all soldered, heatshrink wrapped, and protected with wire loom.

once again this forum has improved my ride. much thanks!

You did catch the wire change from pink\black to orange, right?

I hope that's what you meant by the breakage incident, but...... sympathies on the breakage.

I'll check further, but I think the Lift Pump Relay coil should not draw 1.5 amps.

The banded-end lead on each diode ties to the purple\white wire connected to the lp relay.
The cut-off purple\white wire ties to the non-banded end wire lead of either diode, with remaining diode tied to Glow Relay terminal.

yes, one side of the glow relay is 12v (red) from the battery, the other side is dual orange wires with inline fuselink...one for each glow bank. i connected to the orange pair at the relay.

both diodes banded ends are near the LP relay. nonbanded ends are to power source.
if i have a 3amp rated diode, will that attempt to draw 3 amps? maybe the 1.5 amp fuse was faulty? it only lasted 5 or 6 startup cycles. i'll watch how long the 3A fuse lasts.

Rectifier diodes are rated for allowable forward current loading within acceptable heat rise - wattage.
If the relay coil does draw 1amp, the 3amp diodes would be a safety margin - 'works fine, lasts a long time' scenario.
You done good, Steve-R - hopefully there'll be a few more Diesels running around with extended starter life.

Which fuse opened - Glow or Crank?

the glow fuse.

Remove the fuse, insert an ammeter red lead to Glow, black lead to lp relay, note current to relay at WAIT TO START.

Install Glow circuit fuse, do same for START circuit, compare current drawn by lp relay.