View Full Version : D7-3T Starting problem
10-10-2010, 12:31 PM
I have a D7-3T serial number 23593 and I am having an issue with starting the diesel engine. I have had the dozer for about 20 years and it has always started without much effort. Lately it takes a considerable amount of time to run the starting engine to warm up the diesel enough to fire. I have good fuel pressure,in the green area on the guage and the starting engine transmission is in high and turns over the diesel as it should. I checked the rack and it is free and operational. When it finally begins to fire with out the aid of the starting engine it only fires on a couple cylinders and as it gradually warms up further the other cylinders fire off. If I pour the throttle to it while it is firing on a couple cylinders it dogs down and a ton of black smoke comes out.
Im thinking it may be a head gasket but though I'd throw this out to everyone on the forum for ideas. Once it warms up enough it runs great with plenty of power. It does not get hot or there does not appear to be a loss of coolant in the system.
Thanks for your help
I would say the head gaskets are ok, bleed the inj pump and lines, check the valve adj, and make sure the decompression linkage works as should, and im sure you will get more info on here.
10-10-2010, 01:26 PM
If all you say is working right then most likely it is a tuckered out engine. Just not making the compression pressures needed to get ignition without long cranking periods.
10-10-2010, 05:39 PM
Could it be the injectors getting weak? Mine is doing the same thing and thats what i thought. but its been like that since i got the cat 6 months ago
10-10-2010, 06:06 PM
Look at the blowby coming out of the crankcase breather. Probably is increased over what it was a few years ago. Just another sign of a well worn engine or sticking rings.
Could also have the injectors checked so you know they are in good shape and time the injection pump lifters to account for the wear that inevitably occurs which delays the injection timing.
Check the connections from the air cleaner to the engine, look inside the manifold for dirt...if the starting behavior has changed fairly quickly, these are classic symptoms of a dusted engine.
10-10-2010, 06:29 PM
Those are some good check list items.
If it runs good once you get it going I wouldn't suspect the injectors. Usually if it's a compression related issue the starting effort becomes more noticable with time....and change in ambient temperature.
These engines are huge heat sinks and unless you can make ignition temperature (requires about 750 deg. F. cylinder temp) they will not start at all. You need good compression and heat transfer (no carboned up heat exchanger) from the pony to get er going.
When mine was like that, it was a porous cast head seeping a tiny, tiny bit of water into the cylinders which corroded the sleeves and caused compression loss. I hope your problem is a lot simpler than that.
10-11-2010, 12:15 PM
Thanks to all of you for your ideas.
I hope that it is only a problem with the fuel supply side and I will check the injectors. If not than I've got some major work to do.
Here is a couple shots from last weekend after I got it going
10-12-2010, 11:54 AM
I have a D7-17A that had a similar problem last year. When the main engine was started with the starting engine the main engine would fire on three cylinders and the fourth cylinder would start firing about 30 seconds after the engine was running. This problem had been going on for several years and I though nothing of it until one day I was running the dozer and it started to knock like a rod was coming loose. It turned out to be a problem with one of the individual cylinder diesel injection pumps. After replacing the defective injection pump the main engine now fires right up on all four cylinders without missing. This might be your same problem. Get a new cylinder injection pump and install on one of the cylinders that is missing or swap places with one of the pumps on a good cylinder with one that you know is missing and see if the missing problem changes cylinders.
10-12-2010, 01:22 PM
I'm sure this is a stupid question and I'm not a diesel mechanic but here it goes:
I was playing around with bleeding the system starting at the fuel filter upper and lower housing and got a steady stream of fuel. Then I proceeded to open the fuel injection pump vents one by one and got a stream of fuel out of each individually , then I got the bright idea of trying to see what happens if I open all the injection pump vents at one time and nothing came out. Is this normal or could this be my problem?
10-12-2010, 07:19 PM
When is the last time you changed fuel filters? Tim
10-13-2010, 07:47 AM
I changed them about a year ago. They should be ok
10-13-2010, 08:45 AM
Make sure the air is bled out of the system and try cracking the injector lines at the nozzle. You should flow fuel out of all lines at the nozzle at the same time. If you don't, then I would feel comfortable believing you have a fuel volume problem.
10-13-2010, 10:07 AM
Did you read my comments I left for you Yesterday at 2:54PM? I would check the individual cylinder injection pumps as I had a similar problem to what you describe on the two miss firing cylinders when you first crank the main engine. My problem was caused by a bad cylinder diesel injection pump. If you had air in the system it would work itself out when the main engine starts up.
10-13-2010, 10:33 AM
Yes I did read your comment and thanks. That got me thinking that when I bled the fuel lines at the injection pump vents I got fuel out of each one individually but when I opened all four at the same time I did not get any fuel whatsoever. That got me thinking that it may be my fuel transfer pump. I wasn't sure if I should be getting fuel out of all four vents at the same time or not. I dont want to replace the injection pump if the problem may be somewhere else.
10-13-2010, 12:13 PM
I am not familar with the D7-3T Fuel Injection Pump. Does it have four individual injection pumps one for each cylinder? I did not change the whole injection pump system on my D7-17A but only one of the four individual cylinder injection pumps. I would think that your fuel transfer pump is ok if you are running in the green on the fuel pressure guage. A single cylinder fuel injection pump for a D7-17A was not very expensive, I think I paid around $60.00 for one that I got from Heavy Quip.
10-13-2010, 01:20 PM
Are they relatively easy to replace? Is there any way of determining if one is defective? Ill probably give that a try. It sounded like my problem was similar to yours.
10-13-2010, 01:53 PM
I have never worked on a D7-3T but on my D7-17A the individual fuel Injection pumps on the Injection pump rack were easy to replace. All you have to do is make sure you get the gear on the individual pump timing gear aligned with the mark on the injection pump rack gear. I bought one new cylinder injection pump and moved it around until I found the one that was causing the problem. Old Magnet can provide a lot of information on this he gave me a lot of help on the problem that I had last year.
10-13-2010, 02:29 PM
Yes it sounds like the 17A is similar to the 3T with 4 individual injector pumps that are run off a rack. I believe it is the D8800 engine. I appreciate your help. I originally thought it was the head gasket but after everyones comments I do believe it is probably in the fuel supply. I will try to replace the injection pump(s) and see if that does the trick. Thanks for your help
10-13-2010, 07:22 PM
I would close the injection pump vents again and see if you get fuel out of one when you open it. If so, your transfer pump may be worn out or the relief valve poppet or spring bad, the seat for the relief valve poppet grooved etc. If it flows out of one bleed screw at a time, it should flow out of 4 even better, but your fuel delivery to that point may be so low that it only seeps very slowly when there is no restriction to the bleed off opening.
If no fuel out of a single bleed screw, go back and follow fuel from the tank to the injection pump, checking for fuel flow at each bleed etc.
You can get crud in the filters over a years time, sometimes it grows in the tank. An algae would be worse in the bottom of the tank where any water accumulates and would be the first thing to come out. Similarly it can grow rapidly in the fuel filter housing where there is an accumulation of dirt and water for it to live on.
The bleed screw below the filter plate is before the filters, and the one above the plate with the knurled wheel is after the filters, so if you get good flow out of it, the filters are not stopped up so badly it shouldn't crank. Still might not run well under load, so you'll have to check that out when you get it running.
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