1989 6.2 won't start when warm

[calvinlewington]

My 1989 6.2 will start just fine when cold ,but refuses to restart when hot,if it has been sitting more than 15 minutes.Glow plugs work fine,I've replaced the injection pump, which has made the truck run very well ,but still didn't fix the hot starting problem. Two new batteries improved the cranking speed ,but still no joy. Once the engine has cooled for about 1 1/2 hours, all works well again. Engine has good smooth power and good compresion too.Cold it starts runs perfectly smooth. I've resorted to just leaving it idling while I' shopping...wife is not impressed.

[trbankii]

Take a look at these two posts:

Warm Start Inhibit Switch (http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=003814)

Glow Plug Inhibit Switch (http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=003779)

A lot of these problems have been discussed before. I found these two searching on "warm start."

[BobND]

If (and only IF) you have 60G or better glow plugs, open the hood, jumper the 2 large terminals on the glow plug controller to light up the 'plugs for 10 to 15 seconds, and then have an assistant hit the starter. If it starts, you will know that you can eliminate the glow plug inhibit switch, and do the "increased glow time resistor mod", and it will start better.

Otherwise, it sure sounds like a classic case of a scored head and rotor in the injection pump.

Rarely, the shutdown solenoid in the IP cover will have a coil that has high resistance when warm, or is not getting a good source of 12-Volt power, and does not pull in, and allow the pump to inject fuel. Carefully listen for a distinctive "click" in the IP when an assistant turns on the key. Stanadyne does have an improved heavy-duty solenoid available, if your IP does not already have one.

[ZZ]

Your truck is a prime candidate for a manual glow plug switch. The compression is just low enough not to start without the glow heat.

I think it is too new to have the inhibit switches.

You could try moving the glow relay from the rear of the driver's side head over to the fender well. It may cool quicker so as to fire the plugs to start it after it sits for awhile. I prefer the manual glow switch because it puts you in control every time.

[arveetek]

Another possible problem is the starter. I had the same symptoms once, and it turned out the starter was heat-soaking, and was weak enough that it couldn't turn the engine over quickly enough to start well. Replacing the starter fixed that problem.

A 6.2L that starts well when cold shouldn't need glow plugs after sitting for only 15 minutes. I know my truck only needs glow plugs in the morning, and I don't use them the rest of the day, at least during warm weather. In fact, after my rebuild, I don't even need glow plugs to start at all if it's over 80* outside.

A slow starter can keep a 6.2L from starting because the engine is not cranking fast enough to build high compression, i.e. heat. That heat is needed to ignite the fuel. Using the glow plugs might add just enough heat to aid a slow starter and get it going. However, if the engine doesn't spin over fast enough, no amount of glow time or fuel is going to get it started.

Casey

[Robyn]

I am very suspect of the shut off solenoid. I have seen this. To check it listen to the pump and have an assistant turn on the key, the pump should Click. If its does not click you need a new solenoid. If the solenoid clicks try cranking for a while if its getting fuel there should be white to blue smoke at the tail pipe. no smoke means no fuel.

[calvinlewington]

The problem continues...even with a manual glow plug controller,new injectors ,fuel solenoid opens fine(even tried jumpering it open in case I was loosing power when cranking)lift pumps putting out good pressure too,and cranking speed is first class,but once it's warmed up,it will not start until all heat is gone out of the engine. I think it must be loosing enough compression when hot to cause the problem.Frustrating thing is, It runs great, from cold,tons of power and smooth as silk.

[twaddle]

Hi there,
Does the engine use an unusual amount of oil or is there excessive crankcase back pressure when cold or hot?
From what you describe the engine seems to be in pretty good condition.

Generally an engine has lower compression when cold and as it warms up everything seals and it should have better compression when hot.
This is also why a compression test is usually done when the engine is hot.

If you think the engine is losing compression when warm I would recommend doing a compression test with the engine at or close to working temperature as possible. You should get between 300-400 psi.
If the problem of difficult Hot starting is due to a severe drop in cylinder compression and it would need to be in more than just one or two cylinders, Glow plugs are unlikely to help.
The cause of the lost compression should be investigated.

Try one last thing though, when the engine won't fire when hot, pour some cold water over the injection pump. If the engine fires up the fault is likely to be the replacement pump.

Regards

Jim twaddle
Biggar, Scotland

[calvinlewington]

I agree with the idea that an engine compression should be better hot than cold.I've been an aircraft mechanic for 20 years and hot is the only way we do a compression check on a plane. I tried the cold water trick and it fired up like a brand new truck. I guess I'll have to call the guys who sold me the pump. By the way oil consumption is good, about 1/2 qt every 5000km,not bad for an old beater.

[twaddle]

Do you need any info on why the cold water trick works (sometimes) if the pump is bad?

Jim

[calvinlewington]

My guess would be that the cold water reduces the dimensions and therefore the intenal clearances in the pump to produce a higher pressure,but that's just my guess .I would definitely like to know what happens, the more I can learn the better....Thanks...Calvin

[DmaxMaverick]

It's really very simple. The internal hard parts are steel. The housing is aluminum. They expand/contract at different rates. As a pump gets worn[out], the internal clearances become greater. When the pump/engine/fuel is cold, the clearances are closer, and the fuel is thicker. This allows the pump to generate higher pressures. As the pump/engine/fuel gets warmer, the clearances open up and the fuel gets thinner, making it harder for the pressures to build while trying to start.

Pouring water on the pump causes the aluminum housing to contract (while the internal parts remain expanded), decreasing the internal clearances.

Once the engine is running, the clearances become less of an issue, as higher speeds overcome the leak. However, the pump becomes more and more sensitive to lift pump performance as it wears.

[calvinlewington]

I finally got around to replacing the pump...again...and my problem seems to be solved.The guys I bought my first pump from sent me a replacement with no hassle.I hate doing a job twice ,but sometimes these things happen.I was wondering what would happen if you "turned up" a pump with this problem,would it make the problem better or worse? Thanks to all that helped me figure this out

[BobND]

Originally posted by DmaxMaverick:
It's really very simple. The internal hard parts are steel. The housing is aluminum. They expand/contract at different rates. As a pump gets worn[out], the internal clearances become greater. When the pump/engine/fuel is cold, the clearances are closer, and the fuel is thicker. This allows the pump to generate higher pressures. As the pump/engine/fuel gets warmer, the clearances open up and the fuel gets thinner, making it harder for the pressures to build while trying to start.

Pouring water on the pump causes the aluminum housing to contract (while the internal parts remain expanded), decreasing the internal clearances.

Once the engine is running, the clearances become less of an issue, as higher speeds overcome the leak. However, the pump becomes more and more sensitive to lift pump performance as it wears. To be honest about it, though, the "head" is steel and the "rotor" is steel. There is really no interaction (causing a leak) between the aluminum housing, and the steel internal parts. The hard starts have to do with the thin, heat-soaked fuel leaking past the PRECISION fit of the head and rotor, both steel.

I doubt very much the expansion of the aluminum pump case affects the HEAVY-WALLED head much, if any, and in reality, most of the hard starting issue comes from the low viscosity of the hot fuel, and the increased clearance between the steel rotor and the steel head, due to wear.

When the aluminum pump housing cools, so does the fuel inside, and it's viscosity increases to the point the internal leakage between the head and rotor lessens to the point enough pressure can be built up to "pop" the injectors, and the engine will start.

As long as the engine is running, fuel is being returned to the tank, and replaced by fresh, cooler fuel, keeping the pump's internal temperatures down, AND the fuel's viscosity UP.

[DmaxMaverick]

Bob

I disagree, and stand on my statement.

The internal hard parts are steel, no doubt. Problem is, everything is housed in aluminum, and it will expand/contract at a more dynamic rate than the steel parts.

As far as the fuel temp goes, when you crank the engine, fuel will circulate. Any "hot" fuel will leave the pump and be replaced with fresh fuel, hot or not. Pouring water on the housing won't cool the fuel to any degree, as to cause its viscocity to increase. The heat of the internal parts will prevent any notable viscocity change during the period we are discussing, but the effect on the aluminum housing is almost immediate. In every case, the quicker you get on the starter after pouring the water, the better starting conditions you will have. I've used less than a pint of water, poured in only seconds, and it's fired right off. Not nearly enough time to effect the fuel viscocity. It's the "squeezing" of the housing that provides the effect.

I agree the steel rotor and head ass'y do not "interact" with the aluminum housing, in regards to the fuel viscocity. The housing has a profound effect on the clearance between the head/rotor, which is where the problem lies. Push the head closer to the rotor, and the clearance decreases.

[BobND]

1.) The fuel passes out of the pump's return so slowly at cranking, you'd have to crank it far longer than the batteries or starter would allow for the hot fuel to be replaced by cooler fuel.

2.) What do you see as the "mechanism" by which the thin aluminum pump case being cooled and shrinking is able to affect the clearance between the head and the rotor, when the rotor turns inside the head, which is made of a THICK blovk of steel, not likely to be affected by the shrinking of the thin aluminum case surrounding it?

[calvinlewington]

So now my truck starts just fine.Unfortunately it would seem that I have had a connecting rod failure.As I drove to to town yesterday,suddenly the engine started knocking like mad(first thought the exhaust let go)It sounds like I have some one tapping the block with a ball pean hammer.Oh well nothing a complete teardown and overhaul won't fix!

[DmaxMaverick]

Don't condem the engine just yet. If you have a failed injector, it can, and will, sound like a rod knock. It could also be the cause of your earlier starting issues.

First, you need to determine which cylinder is making the noise, then swap injectors (left bank to right bank). If the noise follows the swap, it's the injector. You can "disable" a cylinder by loosening the fuel injector line at the injector, one at a time, until the noise goes away, kinda' like pulling spark plug wires, with the engine running (and knocking). If the noise stays with the cylinder, you could have mechanical issues (like a con-rod, push rod/lifter, or piston), or the pump itself may be toast.

[calvinlewington]

I tried loosening each injector,but the noise never subsided.I can't really pinpoint the sound to a particular cylinder,so perhaps I am into yet another pump.

[BobND]

Before running it any more, pull the glow plugs and see if one has shed a tip, which is now imbedded in a piston.

Since it came on so suddenly, also suspect a broken valve spring, or pushrod or rocker (or other) valve train failure.

[Barry Nave]

I always injoy reading about problem that come up and even more so what the end results are.
Any up dates?
Though I spend most of my time(when I have time)at the 6.5 forum, eng. troubles are the same.

[calvinlewington]

I have run the truck a couple of times trying isolate and pinpoint the knock.I can't seem to pin it down to one particular cylinder,but it does seem louder from underneath, so thinking conrod bearing.My garage is tied up with a project car so I'm stuck outside.I've located another 89 6.2for $1200 complete.The truck itself is crap but the drivetrain seems good,so I'll probably swap in the other engine .It'll keep me in a truck 'til I can do a proper teardown/repair on mine(a spare engine etc is always nice to have!).I'll post more as I know more.

[Barry Nave]

:cool: ;)

[twaddle]

Before you haul the engine out, try and check out the cam followers, my brothers 6.2 had a knock that sounded like it was from the sump area when you lay under the truck. But we are sure it is a follower.

Remove the oil filter and cut off the end of it, take out the paper element, pull it open and look at the paper if the big end has failed there will be evidence of a lot of small metal flakes.


If the paper is fairly clear of debri I don't think you have a major failure at the con rods.

Good luck

Jim Twaddle
Biggar, Scotland

[britannic]

WRT the original starting problem when hot: I had similar symptoms, which were eventually resolved when I advanced the timing to an optimal value. Turns out that the HPCA would advance the engine enough when cold, to start it, but when hot, the HPCA is inhibited, so the retarded timing made it really hard to start.

[calvinlewington]

I finally got around to some further troubleshooting re:knocking.I pulled all the glow plugs and found them to be in tact .I also pulled the oil filter and cut it open, but I did not find even a hint of metal in the element. I pulled the rocker covers off this afternoon, there is no sign of bent pushrods,broken valve springs or dead lifters. I was thinking perhaps a valve or piston may have broke but when I loosen off each injector, one at a time ,I get a noticeble miss at each cylinder.So the bottom line is...I've come back to thinking bottom end problem or maybe even something else.

[Ratau]

What should the housing pressure be and how would one measure it.

[Scrufdog]

any progress?

[calvinlewington]

I finally got back to trying to find my knock problem.It would seem that at some time a nut fell into my intake without my knowing,It found its way into a cylinder where it became one with the top of the piston .....well damn.

[DmaxMaverick]

I finally got back to trying to find my knock problem.It would seem that at some time a nut fell into my intake without my knowing,It found its way into a cylinder where it became one with the top of the piston .....well damn.

We have a support group for that. Now....Who could that have been the last time???