Getting Harder to stat when hot

[FWBennett]

I've got an '84 Suburban 3/4T 4x4 and the heat in California is starting again I'm noticing that it's getting harder and harder to start when hot - it also seems to crank a bit longer when it's cold - does anyone have a list of things I can check - it has relativly new batteries so cranking speed should be fine - for the cold part (I can't determine if I've got one or two problems) is there a way to check if glow plugs are good while still screwed in (resistance readings???) or maybe both problems may be the lift pump? - do I recall reading that if the lift pump is pooping out it takes longer to deliver to fuel to the injector pump? I reciently replaced the timing chain (couldn't affford the gears)this problem existed B4 the new chain and has persisted. Can someone explain how timing on a Diesel is done? Can it be done - with REASONABLY priced tools by a fairly accomplished mechanic?
- thanks for all your help with my oil burner!

[britannic]

Check your glowplugs (1.2 ohms max resistance per plug) are all functional and make sure the timing isn't too retarded. Retarded timing is most obvious when hot, because the HPCA doesn't kick in to compensate.

An air leak on the supply side of the fuel system can cause similar symptoms; to check use the pressurized tank trick (search these forums for more info). Other causes include a worn inj. pump, lift pump, blocked fuel filter(s) or injectors - or a combination thereof.

[CleviteKid]

FW:

I see you list an auxiliary electric lift pump on your truck. Can you turn on this pump before you start your engine? If so, does that make any difference?

The original mechanical lift pumps for the 1984 trucks had a bleed-back vent in them to allow fuel to drain back to the tank. That was a bad idea, because it took a lot of cranking to get fuel back up to the DB-2. The later mechanical lift pumps, like for a 1987 truck, did NOT have that bleed-back, and are the preferred "ventless" mechanical lift pumps for our trucks.

Dr. Lee :cool:

[Doug Towne]

My sub had the same symtoms a couple of years ago and the starter motor was the culprit. Not enough cranking speed. I think with the gradual decline in performance you may not realize how slow it's become. I remember thinking at the time that my engine appeared to be cranking just fine.

[gavio]

I had the same problem with my van last summer. All new glow system, electrical, the works and when it would get hot....

Got to where when it was hot enough for the glow plugs to not cycle at all, it just flat wouldn't start until it cooled off enough for the glows to kick in again.

Put in a starter and problem solved. When it gets hot, not only will your glows runs less (if your system is still automatice), but your starter will crank even slower as well.

I went a step farther and put in the later style gear-reduction starter - what a difference! Then I could tell how slowly my old starter had really been cranking.

YMMV, but that's how it was for me...

Good luck!

[FWBennett]

Thank You for all your help - I tried Dr. Lee's suggestion of kicking on the aux fuel pump first (previously I'd only used it to prime new fuel filters) - it still had problems starting (if I held the key the starter would vary in cranking speed) So I got a new starter - not sure if it's a gear reduction model. So now when it's warmend up (hot?) it fires right up! BUT if it sits cold on an incline, it takes quite a bit of cranking BUT if I kick in the aux fuel pump it barely nees any cranking so I'm thinkin' I must have the belled back fuel lift pump Soooo?
DO I just order one for an 87 Suburban? Is this bleed-back valve visable - hos would I know if I'm being handed the correct one?
ALSO - now that I've got a new timing chain is it advisable to take it in and have the timing reset?
Is there a way I can check the timing?
- THANKS!!!

[britannic]

I did a search for you: 6.2L Air Leak (http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002607#000012)

[FWBennett]

Ahhh much thanks to Britt for the search containing the correct part numbers. In reading the article - I'm curious about the procedure of pressurizing the fuel tank and keeping track of the psi? I've tried several fruitless searches - is there some custom plug in place of the filler cap or is there a tool company making such a contraption????
- thanks

[britannic]

Get a cheap cap from NAPA and drill it to accept a tire valve and "Bob's your uncle!".

[jonflies]

Did the starter or glow plug check, indicate any fix in the future? I've got similar problems but I'm leaning towards the IP advance.

[FWBennett]

OK - So far I've replaced the Starter, the 2 positive battery cables - that didn't cure it and at one point while running errands I got "stuck" at the grocery store - it would crank but NOT START so I had to call AAA for a jump start and it fired right up with the extra juice. Then my appointment at the shop came and they set the timing - it was pretty advanced? (the pump got turned towards the passenger side from where it was when I changed the timing chain. It runs/starts better but it still cranks too much or it took me 2 and 3 trys to get it started but the good news is I haven't had to call AAA!
So basically I'm still working on this problem, I've since replaced both negative battery cables but haven't had a chance to test it (mine is not a daily driver). Earlier while cranking, I would notice variations in the speed of the starter - I haven't determined if it's an electricity supply problem (Walmart Batteries loosing performance when hot?), a hot starter problem (the down pipe of the turbo system is in close proximity - my next step will be to insulate the down pipe with fiberglass wrap from JC Whitney - the package just arrived) I have an electric auxillary fuel pump installed as per Dr. Lee's directions - if I kick it on before cranking, it doesn't seem to make much difference so I guess I can rule out the lift pump so I guess my next step will be to inspect the Injector Pump and Injectors - does anybody have any suggestions on how to test these? While it was in the shop the mechanic said he does notice "a miss" as it's ideling so maybe an injector?????
It's got about 150k mile on it so I guess something is wearing out....

[jonflies]

Have continued searching as well. Today I got stuck at a local shop. I attempted to move the IP while there, but couldn't get it to budge. Had to wait 2.5 hours for it to cool enough to start again.
I've read on other posts that IP's will start acting up like that, but I thought advancing the timing would help. I think the only way to efficiently check either the IP or the injectors themselves is on the bench.

Just had my injectors rebuilt earlier this year, so I'm going to change my fuel filter tomorrow, and if that doesn't help, I'm going to start shopping for another IP.

[ZZ]

I had several of the 80's 5.7L & 6.2L diesels. Most of them had little or no glow time after driving them. I changed the systems over to manual. I found this to be my my cost effective way. I put a spring loaded toggle swith under the dash. I ran one wire to a fuse that only had current when the ignition was in the "on" position and ran the other wire to the glow relay. I turned the switch on for 6 seconds with the older 8G & 9G plugs and then had the instant start. I learned real quick that these plugs were 6 volts and burned out with my more time. I put 7G's in my first 5.7 Diesel. They were 12 volt plugs and needed 30 to 45 seconds to get hot.

I also had an '85 Chevy that I would have to boost at times after I drove it. I discovered that it had a bad battery. Changed it out with a new one and no more problems.

On another time with the '85, the mechanical lift pump would lose prime at times after driving it. An electric pump cured that. This also made priming the filters easier after changing them.

[jonflies]

Changed my water separator filter yesterday and fixed my problem. While I was at it I checked the one on my 99 and found it needed replacing too.

[doncannon]

Jon,
Diesels like power (Electrical). When I was a partsman I talked with a battery supplier and they said the batteries that the 6.2 called for were just barely adequate. (The batteries in a diesel are as important as glow plugs because it would be hard to start with a bad glow plug same for batteries). So I found for my customer 2 batteries that would fit (The battery is listed for a 88 Ranger a 65 series that has 850 cold cranking amps/980 cranking amps times 2-one on each side) Turned out I bought that same truck about 6 months later...sure pays to take care of customers. I just looked and that was in March of '01 and they are still going strong.
Hope this helps,
Don
PS I have tested batteries to be good 12v, but they can have a bad cell and on a load test would fall down past 300 cca. When one is bad it just makes it harded on the other if it will start.
One my Vw Rabbit I replace it (also the same 65 series) every 3 years. It just won't ignite the glow plugs when it gets past 3 years much less start the car.

[ 07-26-2004, 06:45 PM: Message edited by: Don Cannon ]

[FWBennett]

OK I FINALLY got a chance to test the setup (new negative battery cables) and it FAILED! Drove a bunch of Boy Scouts home from Summer Camp so I had a pretty good load plus A/C for about 1 1/2 hours - in 102 degree heat, parked and tried to start it about 45 minutes later - it would crank just fine but would NOT start! We tried jump starting it from another car to no avail. I'd try every 10 min and after about 30min with the hood up it finally started again!

[FWBennett]

OK I'm running out of Options AND Money! I took the year-old batteries back to Walmart and they cheerfully exchanged them for bigger ones (875 cca to 1000) and that didn't help. I finally took it in the shorts and took it into the shop - he wasn't totally able to duplicate my problem (not sure how much he tried) but basically confirmed my suspicions about the Injector Pump and swapped in a new one for me $$$. I left the shop and drove about 5 miles - did some shopping and it fired up nicely but the outside temp was getting hot so for the ride home (about 10 miles of STOP & go) I fired up the A/C mind you - this is a Subdivision so I've got the front and rear A/C fans going - got home, parked it and 15 min later went out and it wouldn't start! Ran the batteries down! Threw the Batt Charger on it (the quick charge/engine start mode) and after the initial charge it fired up with hardly any cranking - so I thought AhHa! I've been chasing a fuel problem when it's been a charging problem all this time! With all the A/C poop on - the voltage drops to 12.84v (can someone tell me if this is enough?) but without the A/C it's 13.5 => 13.7 which I know is good so I drove around with the A/C off. Last night was an example - drove 10 min to run an errand (outside temp was in the low 90's) - I didn't use the A/C but was in the stoor for 45min - hop in - the glow plug relay doesn't come on BUT for good measure I used the override switch then hit the starter - it simply cranked I hit the switch to the aux electric fuel pump and would NOT start! I let off on the starter - gave it a couple minutes rest with the aux. electric fuel pump on, gave the glow plugs some juice - said a short prayer and it fired up like it was new! The mechanic did find a couple of bad glow plugs - once I swapped them out it COLD starts just perfectly! - but this warm start is driving me nuts! Any body got any more ideas???

thanks for all your input so far!

[cschneider]

Why don't you email me directly and we can try to figure this one out fast? I have had this same problem and have gone through quite a few different fixes over the years. bluerover@rocketmail.com

[ 09-04-2004, 08:33 AM: Message edited by: cschneider ]

[Mark Krieger]

Here's what I know about lead-acid batteries...

The threshold for charging a 12 Volt battery is 12.9 Volts. At this Voltage, it'll take days to charge a battery the size of a car battery. Below this Voltage it won't charge.

A hot battery needs a Voltage that's closer to 13.8 Volts to charge within a reasonable amount of time. (A cold battery will require an extra Volt or two. At freezing, it'll take 15.6 Volts to charge the battery equally as fast.)

I believe I've read that modern alternators are temperature compensated. I think that a hot alternator will purposely reduce its output Voltage even if it isn't overloaded.

It seems likely that you're barely recharging your battery.

[cschneider]

That's a good point. I upgraded to gel cell batteries about two years ago and have never looked back. They are so vastly superior that the additional cost seems laughable in retrospect. Of course gel cells have an even lower threshold on the top end but they almost never leak their charge and are infinitely more resilient.

[Salemone]

Where does your electric lift pump get its power?
I had the same problem you had. I have one battery. It starts cold ---would not start hot. I
put a check valve in the line so that fuel would not siphon back to the tank. Still no fix-
problem solved now---had the lift pump power
connected to accessory instead of ign. pump stopped when cranking. Hooked to ign--starts hot
and cold.

[FWBennett]

The aux. electric fuel pump is hooked up to a constantly hot source (I believe that's the way Dr. Lee recommended) it makes it handy for purging the air/priming a new fuel filter. I believe I've got several little problems that are contributing to this as a whole. Thanks for the info on the voltage needed to charge the batteries - OBVIOUSLY I'm using more juice than I'm putting back in when the A/C is cranked.
I did have some small success yesterday - it was 102 degrees and I made a Home Depot run and a run for gas (not diesel) for my Jerry Jugs. Both times I flipped on the aux. electric fuel pump as soon as I opended the door - took some extra time to check the seatbelts etc. and both times if fired up on the first try! So I guess I'll look into swapping out the old lift pump with a newer one that keeps the fuel from leaking back to the tank!
Hey cschneider what is it that you mean about the Gel Cells having a lower threashold on the top end?

[cschneider]

Gel cells have a much lower tolerance for being overcharged than standard lead acids do. Apparently they can only handle less than 16V at the max before they overheat or something. I'm not exactly sure what happens or what makes these batteries vulnerable but it's my understanding that they are.