Hard starting detroit

The 3-71 I rebuilt (finally) runs like a watch. Now the 8-71 (acually built 1964) is most difficult to start. (on my dump truck) I put a new starter in it, a booster electric fuel pump, new f.o. filters and a new air cleaner and the pos is so hard to start that the last time i tried i parked it for the winter. I think it must have low f.o. press, there is no guage. Once it starts it runs real good, strong, doesn’t miss a tick but its just real hard to get it going, last time it took one full new can of either to get it going.
any ideas? it isn’t sucking air (note booster pump), the f.o. is new, would appreciate any ideas.

Compression test okay?

I’ve only hauled about 30 loads of dirt in the last 15 years and less than a mile round trip per load. It only ran during the summer. I’m suspecting fuel pump pressure based solely on the lack of black smoke while cranking. other than the aforementioned fuel filters, air cleaner and fuel booster pump i haven’t done anything.

What’s the temperature where you’re trying to start it?

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In the 60’s. Usually it’s 70’s or 80’s. Neighbor who had it never had problems, it’s something that has been slow progressing.

Without the ether, does it sound like it wants to start or is it completely the starter doing all the work?

If you have a rpm gauge on the engine, what’s the cranking rpm compared to what the starter is supposed to turn? I know yours is surely battery start but I had a problem a few times with air starters turning Cats & Detroits but not sufficiently fast enough to get them to start. The same with weak batteries.

If the engine is turning exactly as rated on the starter or faster then those might be signs of trouble too because the engine should be giving some resistance?

Have you noticed any excessive pressure coming from under the oil fill cap when turning it over?

thanks for the input all of you. in answer to your question sand pebble the engine seems to be turning same speed as the last starter i had on there. the old one was loose with only two bolts (loose) holding it. the new one … well, it’s the same and the old one always started it, I just thot there may be some drag but doubtful now.
When running there is not much blow by, the engine prob has a rebuild on it based only on its year (1964), i forget the miles but it looks like quite a few but the truck seems to of been maintained pretty good.

Without either it CAN sound, and has sounded (in the past) like it’d start but anymore it won’t do jack without the juice. Your idea of insufficient start speed is valid if the engine is used but then again, I am quite sure the speed is normal cranking.

as mentioned: when it runs, it sounds GREAT. it’s a strong runner with a 5 and 3 speed and sails up any grade.

The air cleaner was about 35 lbs. full of walnuts, i thot for sure a new air cleaner would help but doesn’t seem to make a diff. I’m now looking for a spring actuated fuel back pressure device to stick on the return line along with a guage and set it all up for around 50 psi?? My 3-71 uses 50 psi back pressure but usually stays around 25 … i think i need another fuel pump, the back pressure restrictor is just like the oem one , right now i had to smash the return line down some to get 25 psi. fuel is going someplace i guess but i don’t see indications of it going into the air box tho it leaks on the outside and will go empty in a couple days (or less)!! but back to the V8 … If it was getting fuel it’d surely smoke like hell, it always did so im back to F.O. issue, i haven’t done athing to it since i shut it down when it was running last time. well, i added new fuel filters and the air cleaner and the booster pump and yes, when it was running there was a TON of fuel going back to the tank on the return line. I know this because the actuator cable to operate the PTO and lift cylinder got wrapped around the PTO drive line and took the return line with it … that’s how i know a LOT of fuel was going thru the return line !!! and was doing so when i shut it down

95% chance its a fuel issue. Is there a small air leak in the fuel line somewhere? Pump sucking air when you’re trying to start? Shouldn’t there be white smoke when it’s being turned over with the starter?

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ya, WHITE smoke … turning to black when it starts getting hot, right before it starts. there is a very good chance it could be sucking some air and this would be in line with it going to krap over a period of time

gawd this keyboard sucks!!, ya, white smoke , black when nearly starting … yes, could be sucking some air so i put that booster pump down next to the fuel tank. there is only about a yard of fuel line before the suck side of the pump. the engine pump probably out paces the electric booster pump tho … i am thinking blocking the return line and using a guage getting 50 lbs or so on the back pressure… of course, if you’re right then it could still suck air which could to a point displace the fuel but gawd… those lines are 15 ft. with all manner of fittings and such, it’d take more money to replace them than the truck is worth but … well … it could be sucking too much air but then, when you shut down, fuel should run out those small holes and eventually show up, but then, this truck is so dirty it may not be noticable, and i’ve also seen leaks that would only leak in one direction too … that’s a good one !!

Cold engine, slow crankiing, low compression. Given your description of the usage history, most likely all three issues combined.

Hopefully it starts for you easily every time after you warm it up & put a load on it. If so, Steamer may be right. If it gives you starting problems again after 30 min to 1 hour after shutting down hot then I would guess KC may be closer.

Lovely. Cover it up next time along with the exhaust outlet.

Another option rather than breaking rings or cracking pistons with ether, take the air cleaner off and aim a weed burner at the hole while cranking.

Or at the very least find some way to preheat the thing.

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does it have the correct starter?
what size battery bank and cables?
plus put a temp tank above the engine with supply and return then try it the next day as could be fuel drainback?

I’m down to 1 353 at home now, the 671s and 892’s we had it trucks have long since went to the retirement homes, everything should have a 6Nz in it. My 353 will start to about 20 with no summertime spray, at 0 she likes it, and that’s after sitting 3-4months sometimes.
An auxiliary lift pump is just masking a bigger issue. Have you checked the linkage, popped the valve covers and made sure the rack isnt bound up a little ? Only takes a couple revolutions for the governor to build up pressure, normally on a dormant “land based” detroit 4-5spins and stop, should see a little smoke, spin it again and get some combustion, all depends how cold. At 60-80 degrees that should light pretty quick. When you rebuilt it did you check the blower lobes ? Theres a couple 90s / fittings in the filter housings that could have crud restricting flow. I would tear into it, you can check the fuel system with a low pressure air blower tip, run it off a 5gal pail till you can determine if its “engine” or “fuel system” troubles. Had my fingers in a 471 ssdg last night because of “detroit mechanics” and attempting to fix shit when it’s not broken. Your probably dealing with a simple fix but that spray can will only make it worse :rofl:
I had an 892 in a Ford LTL literally shear a piston skirt off, guy drove it home and she just kept knocking, looked like metal carnage but she didnt stop. Somewhere I’ve got a 92 cap, twisted up and gnarly, engine still ran just minus 1 hole now


Most likely it’s badly worn and or has stuck rings from excessive sitting.

It’s hard to hurt a 671 with either, but once you start using either the tend to become dependent on it. The world is full of worn out 671s that start hard but still do the job.

A couple of winter tricks for starting very cold engines: 1. Get a rubber flex exhaust hose (like those used in garages), and put it over the tail pipe of your pickup. Run the other end up under the 671 and use it to preheat the engine and intake air under the hood for at least 1/2 hour. Better, 2. Rig up hot water hoses off the heater for your pickup with hydraulic quick connect couplings, do similar on your 671 (inlet as low as possible and outlet not blocked by thermostat) and pump 180 F water from your pickup through the 671 to warm it up to about 120F 3. Buy either by the case and just keep using it until it does not work anymore. Your worn out 671 will probably continue to start on either for another 15 years.

There are some other similar cold start tricks.

Ps. The return line on a 671 always has lots of excess flow.

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Rebuild the engine, it’s not that expensive or complicated to do so. If you need to start it do not use ether. Throw some gas on a rag and give it a sniff thru the breather.

The gas on a rag squeezed next to the breather is a good trick, particularly for a CAT, or small high speed diesels with aluminum heads, for which ether ca be too aggressive

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I had a 53 series that needed a prime. Had a gear oil bottle full of diesel fuel I was holding up like a bag of saline for the engine. When it finally caught and started it sucked the bottle flat.

Is it all tubed or is it hoses? Have you tried running it on just a bucket of diesel? Might rule out anything upstream being the issue.

It’s not something like a throttle or a stop cable being wonky?

There are thousands of old two cycle GM Detroit Diesels still in operation, and many of them are routinely started on ether, especially in cold weather.

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