DetroitDiesel71

Evening all, well after starting truck after work F/O Pressure was 15psi at idle and would fluctuate with voltage drops as the grid heater cycled. Temp out side was about 26f. After warming up F/O pressure was about 12, so figuring it is just still cycling with the grid heater. Well I leave base sitting in the staten island expressway(parking lot), which is slow traffic and nice actually because it allows me a slow warm up. Anyway while driving about 25mph, truck is now about 180f on my mechanical gauge, F/O pressure gauge just clicks of sort of, I mean pressure did not drop below 7, but when I ran faster it just seemed to click back up to 14psi, as if it was having voltage drops.

So down the turnpike I go , psi 13 all is fine, then just clicks off, (don't really know how to explain this) Batteries are original and this is their sixth winter. I am gonna load test them tomorrow. All said and done, I get home, shut truck down, let sit, click to restart and 15psi on F/O gauge , restart it, runs ant 15psi, then as soon as grid heaters cylce, back to 6-7psi. If it is the batteries, are the opitmax yellow tops worth it?

Thanks for all the great advice here. It helps being so far from TX at my dad's shop where it is warm .

MK2 Stephen Lucarino USCG

ctdhombre

Yellow tops are good batteries.

Wow, six years on a set of batteries is good!!

RATTLINRAM

I'm noticing almost the same thing with my 99 and a Westach electrical Fuel pressure gauge. I'm on my original batteries also, but I'm only seeing a drop to 11psi at times. I have noticed that when the defrost is on (which cycles the AC compressor), the FP will fluctuate. The lift pump has over 60k on it since being replaced at around 42k.
I'm hoping that the lower psi readings are a result of the batteries, however these lift pumps can exhibit the same kind of symptoms when they go bad or they just stop all together. It may help to clean all the connections on the batteries and the lift pump to make sure we are not losing juice there.

I know this isn't much of an answer to your question, but if you're dropping to 7psi,,,, I would be looking for a fix quickly. Plus,,,, at over 150k on your original lift pump,,,, (That's got to be some kind of Record!),,,,,,,, it might be a good idea to have a new lift pump on hand.

Please let us know what you find.

Geico266

Sounds about normal to me. These beasts act alittle different when cold due to heaters cycling, ect. I would just watch it and when it gets to 5 psi replace the LP.

Six years on lead acid batteries has got to be a world record for a CDT. Make sure they are not leaking onto the wireing harness under the driver side battery. It's a good idea to pull it once a year and sprinkle some baking soda in there and wash it down.

DetroitDiesel71

Guys, thanks for all the help. Sorry about not updating my sig. The Lift pump is about 2 months old. I am a nut about wiping the entire engine compt down monthly, so the batteries are removed about every three to remove any build up of road residues. The terminals are tight, and clean. So I guess it is time to buy a set of batteries. I just am a bit conflicted between optimas and reg batteries. If I go with the optimas, does just daily driving really drain them enough to achieve their charging purpose? And I guess the original batteries lasting is due to 90% highway so they are never really short charge??? just a guess..