Diesel will crank but hard to start

[captsue]

My boat has a cummins 4bt3.9 ... have owned the boat for 8+ years and it always starts quickly ... except for today. I have not been able to use the boat much this year ... last short day cruise was in October with no issues. This morning, cranked over easily but would not start ... it acted like it was not getting fuel. Engine only has 10 hrs since primary and secondary fuel filters were changed back in April. Went ahead and changed the secondary fuel filter on the engine anyway ... checked the primary racor filter and it was clean as new with clean fuel in the bowl. Tried starting engine again ... same issue ... easy crank but no start. I did not want to crank for extended time so I closed the raw water intake sea-cock and tried to start again ... it took about 10 seconds to start ... quickly opened the sea-cock ... engine running fine ... however, noticed that there was no tachometer reading (zero) ... also, there was no charge current from the alternator. I sat down to think about what could be wrong while letting the engine run in neutral for 15 minutes or so ... during this time, i jiggled, pulled, and pushed all the wires at the starter and starter solenoid ... all where tight and no change to tach or charge current. I shut down the engine and tried to restart ... again, easy crank but no start. I closed the sea-cock again and repeated the procedure ... cranked easy then finally started after about 10 seconds. Once the engine starts, it runs fine. I am hoping for some advice before I call a mechanic. The alternator is a Balmar 604-150-SR with MC-612 regulator.

[skipperpete]

Firstly, good work turning off the raw water inlet. I don’t know which injector pump you have on your 4BT ( there are 3 types) so I’ll assume it’s the early model with the DPA pump. The usual drill is to establish that the suction side of the fuel system is working perfectly, re check the filters and manually prime the bleed points until there’s only a steady flow of bubble free fuel and give it a start. If you continually get bubbles from the bleed screws there’s a suction leak between the priming pump and the tank. The CAV DPA pump can be a trifle touchy and is susceptible to 2 or 3 hard starting issues but first, establish no suction leaks and a good fuel supply. The 4BT I think had a flywheel housing tach sender (the 6BT did for sure) so the alternator not charging and the tachometer not reading are difficult to explain but definitely check the harness plugs. Additionally, those Cummins lift pumps are not the most reliable and are not repairable

[donradcliffe]

I've had issues with spin on Racor filters on 2 separate boats recently, both to do with the filter seals breaking down and allowing air in-leakage.

The tach and alternator are separate from the fuel problem. If the tach is driven by the alternator, fix the regulator/alternator first and you may get your tach back..

[suiramor]

I had a problem with exact same symptoms (cranking but not starting, then running fine when started) with my Westerbeke 65. Posted a couple of questions here and eventually fixed it by systematically working through the fuel supply and start system. In my case the root cause was a faulty solenoid supplying power to the priming fuel pump and glow plugs. It was occasionally and spontaneously switching on and eventually burning my glow plugs. I kept replacing glow plugs, the problem would go away for a few hours and then return back. Finally, replaced the solenoid, got new glow plugs and engine works like a charm! Not sure whether your engine uses glow plugs but working through the whole system is what I learned.

[captsue]

thank you for the responses ... my engine is 1988 ... and it does have the CAV DPA pump ... also, the tach is driven from the balmar alternator. Today when my engine would not start, i changed the filters even though i knew the filters only had a few hours on them ... this was all i could do today ... and i knew it was a quick and easy thing to do ... so i changed them and crossed my fingers ... and when the engine still did not start, at least i knew i could cross the filters off the list of a possible cause. My surprise came after the engine started (and ran smooth as ever - after starting) and i realized that the tach was not working and that there was no charge current. I don't know how the hard start and tach/alternator issue could be related, but i can't help but 'feel' there is a common electrical problem that is causing both (although i have no basis for this).

[skipperpete]

I agree with your idea that this is an electrical problem, certainly the tacho and alternator not charging. I’ve read elsewhere on this forum that sometimes solar charging can affect the alternator if the batteries are totally charged.
Do you have an electric lift pump that might be affected by an electrical fault? You might have a small stop solenoid on the hydraulic head of your injector pump but I can’t see how that would make the engine hard to start, if it was faulty it would either stop the engine from starting at all or prevent it from being shut down.

[Scrimshaw4]

I had the same problem with my diesel engine. It turned out to be a faulty solenoid relay that was not energizing the electric fuel pump.

[captsue]

I have a bit of an update. Today i tried to start the engine again ... crank but no start ... same as before. Although i was not sure if it would help, i turned on the 60amp xantrex battery charger ... thinking it might give a little extra current to help the engine start (although very minimal compared to the needed cranking amps) ... i turned the key ... the engine turned over a couple times and started right up ... tach functioning correctly and charge current being delivered from the alternator. I turned the engine off ... turned off the xantrex ... turned the key ... crank but no start. Then i turned on the xantrex again ... turned the key ... again, it turned over a couple times and started ... good tach and charge current ... I repeated this test several times, and the result was the same ... the engine would only start with the aid of the xantrex charger. Now i am thinking i may have a bad battery. I called Balmar ... they said if the MC-612 regulator does not see sufficient voltage it will not signal the Balmar alternator to produce charge current. I plan to remove the battery from the boat tomorrow and take it to have it tested. Hopefully this is the issue ... i would rather replace a battery than try to track down a bad connection (the battery is 8yrs old).

[skipperpete]

Good sleuthing captsue, often its the least likely thing tat causes the problem. I still don’t see why a battery with enough oomph to start the engine doesnt’ have enough to excite the alternator, is there a regulator setting on the 612 that can be changed to safely make the alternator charge at lower battery voltage?

[Wotname]

I'll go out on a limb here and make some (slightly informed) guesses.

Nowhere in the above fault finding has any mention been made of voltages. Any electrical fault finding should start with reading the voltages (under load) of the suspect components however without the actual numbers, we can still make some conclusions albeit with less certainty.

What I know - battery 8 years old; engine rotates but won't start without the aid of the 60amp xantrex battery charger; alternator will not output unless the engine start was assisted with the 60amp xantrex battery charger; the Cummins 4bt3.9 is a relatively low compression (~17:1), direct injection without glow plugs.

What I have assumed - the rpm during the start was too low to cause ignition due to battery voltage being too low due to the internal resistance of battery is too high. For the same reasons, the alternator would not excite due to the external regulator not seeing enough volts due to the battery volts being deleted during the extended attempted start. A traditionally dumb internally regulated alternator would have accepted the low volts and cranked out some output once the rpm was high enough (after starting). The Balmar external regulator wasn't so forgiving and would not excite the alternator due to the low battery volts which would be especially low after attempting the start. The extra 60 amps from the charger was enough to raise the start rpm to the minimum required to allow ignition. Likewise the charger provided sufficient voltage to allow the external regulator to excite the alternator.

Which is just a fancy way of saying the battery is stuffed (too old) to start the engine. Which would have been evident if the battery volts were measured during the start period.

Starting rpm is critical to create enough heat to cause ignition especially with a lowish compression ratio and no heating aids (glow plugs or air intake heaters). In this instance, the battery did not have enough oomph to turn the engine over fast enough. I suspect the battery has been deteriorating over time and the start time has been increasing over time until the battery has finally said enough! Staring rpm is often overlooked, we assume if the starter motor is turning the engine, it should start! If it doesn't start we go looking for other culprits (e.g. air, fuel, compression).

Additionally, it is all too common to fail to notice a slowly developing fault (e.g. an aging battery) if the time to failure period is long, like a years. An example, my tractor (low designed compression, direct injection) requires glow plugs for a cold start, as the battery ages, the start time increases from less than second (new battery) to greater than 5 seconds (vey old battery) but the start time is only slightly incremental each year. I get used to the increased start time and get very suprised how fast it starts when it finally gets a birthday present of a new battery.

EDIT - Hindsight is a wonderful thing and is usually 20/20; in this instance I expect it is 18/18. Regardless, it is a good learning tool!

[Wotname]

Originally Posted by skipperpete

Good sleuthing captsue, often its the least likely thing tat causes the problem. I still don’t see why a battery with enough oomph to start the engine doesnt’ have enough to excite the alternator, is there a regulator setting on the 612 that can be changed to safely make the alternator charge at lower battery voltage?

My guess is the battery was so stuffed the voltage was quite low (say<9V) immediately after starting. A traditional dumb internally regulated alternator will accept any volts and providing it can get a some field current (say <1A), it will start to output and due to the self exciting nature of the internal regulator, it will soon (in seconds) output it's designed voltage, providing the alternator rpm is sufficient. The Balmar external regulator is not so forgiving!

[captsue]

Initially, when i realized i had a problem, i was getting ready for a short day cruise ... i had just disconnected the shore power ... and the start battery had been at rest without the charger for no more than 5 minutes. After the first failed start, and 'before' trying to start again, the Xantrex battery monitor showed 12.75 volts on the start battery. 'During' subsequent start attempts, i noticed the voltage dropped to 10.2 volts and as low as 9.8 volts ... I have never monitored the voltage while starting in the past, so i do not know if this is considered low or not ... although it seems low to me. But what i have read online since, this appears to be acceptable (?). I can understand if the battery has weakened to the point where it cannot spin the engine fast enough to start. Before i left the boat today, i stayed long enough for the battery to accept a charge to 13.4v with no current being delivered to the battery. I then turned off the charger (and all loads disconnected) ... after 15 minutes, the battery voltage was 12.95volts. I plan to go back to the boat tomorrow (after 24hrs) and check the voltage again. I am hoping this is just a bad battery, and not a bad connection somewhere.

[captsue]

Another update … the battery was ok … it passed the no-load rest test … 12.8v after 36hrs with no load connected … it also passed the full-load test from the automotive shop … but since it was 8yrs old, i bought a new battery anyway … just for future peace of mind. So …… yesterday, i had the whole day to devote to this issue … i pulled out the fluke meter and got started. I concentrated on the battery cables and the start circuit (start signal/interposing relay/starter solenoid/starter). This time … my wife was with me … she manned the helm … her job was to start the engine while I measured for voltage drops in the engine room below. A lot of measurements were taken … and connections were removed and cleaned … whether necessary or not … some were needed. Surprisingly … during all of this … my wife seemed to have no problem starting the engine. She pointed out to me the start switch had a ‘sweet spot’ … slightly between ‘on’ and ‘start’. Sure enough … if the key was turned fully to the ‘start’ position it would only crank with no start … but … if the key was turned just slightly towards ‘start’ … it would start. I will replace the start switch today … I will also spare you all the other small details … but i am not considering this effort done … I can say this episode has reminded me that Wotname’s comments are so right … very small changes over a long period time can go unnoticed, or deemed seemingly insignificant, and become a new norm … until something finally stops working.

[Wotname]

Interesting and if replacing the switch cures the issue - great outcome!

To my mind, it doesn't explain the lack of alternator output and tach issue but without knowing exactly what is going on, it is difficult to speculate further.

A left field question - is the stop solenoid on the Cummins 4bt normally energised (current flow) or normally relaxed (no current flow) when the engine is running?

If the engine has the more unusual failsafe stop solenoid arrangement where the stop solenoid has to be energised for the engine to run AND the key switch is faulty with the fault disconnecting the ON contact (thus de-energising the stop solenoid) when twisted too far in the START position, then fault can be explained.

[captsue]

Wotname … you are correct about the fuel solenoid … it must remain energized to allow fuel flow. Turning the key switch past the ‘sweet spot’ and fully to the ‘start’ position was providing a weak /intermittent or lost ‘on’ signal to the fuel solenoid. My vision is not the best anymore, so I am taking a lot of pictures … then reviewing them at home. Last night, i found a picture of the external balmar regulator that I hope will resolve the alternator issue. The ‘voltage sense’ wire appears to have a poor connection ( i tried to attach a picture here – blue hood connector). The brown wire goes to my flaky ‘on’ contact of the engine start switch. My plan is to continue this effort … taking baby steps to trace out and learn more about the wiring … documenting along the way … and making my own sketches/wiring diagrams for my particular setup.