Filter or electrical?  

What pump are you using? It looks like a regulator issue. 

 

Filter would fall to low pressure or zero under load. Electrical typically is really wild swings hi and lo. This mild swing up and down looks like a regulator sticking or hanging up and the kicking shut when the pressure falls and builds again. 

 

Be aware you can program the hysteresis of the gauge needle and slow the reaction time or speed it up. There is an extra plug on the back for programming. 

12 hours ago, Mopar1973Man said:

What pump are you using? It looks like a regulator issue. 

Still has the DDRP in it

Look at the regulator. I've got a similar problem right now and know might is because how I bent the last coil of the spring. It's causing the regulator to wander up and down the same way. When my check ball gets on center and stays then the whole floating up and down goes away and nearly rock solid 17 PSI at idle and stays above 15 at WOT. Lately it random drops will make the drop worse at WOT operation. I know it all the regulator screwing up on my AirDog 150. 

 

DDRP has the other flaw being your plumbing is too small if it's still hooking up to banjo bolts and stock fuel lines. 

Forgive my ignorance on this one Mike, I have not spent much time yet learning this fuel system.  Is the regulator internally in the pump? or is it external?  

 

On a DDRP I'm not sure if you can get access to the regulator or not. There might be a screw adjustable regulator you might run it all the way down as low and then back up just in case the regulator is sticking. 

 

This is a AirDog 150 which is most likely a different animal from the DDRP.  I use washers to shim adjust my fuel pressure up and down. The last coil of the spring I typically just egg shape it a bit. This spring I bent a L in the tip of the last coil and creating my problem. 

well its finally starting to cool down here, I need to get with IBMobile and have him supervise me getting some things done on the truck. Upgrading the fuel system may be one of those things now....  It seems to be idling in that 15-17 range but drops to 8-9 on a good hard pull (empty truck) so to preserve the life of the VP fuel system is likely next on the list.

 

It seems the non-returning fuel pumps like DDRP's tend to have a problem with cold temperatures. They will attempt to return a large amount of fuel back to the inlet side of the pump when the fuel thickens. This will typically create cavitation. This is where the pump will create its own air in the pump. The returning pumps like the AirDog and FASS don't seem to have this problem nearly as much. It's returned full to the fuel tank and not to the inlet of the pump. Another reason I'm not a fan of drawing from the basket is if the fuel is foaming up from return it will drop fuel pressure. My return and supply are not in the same basket. 

47 minutes ago, Mopar1973Man said:

It seems the non-returning fuel pumps like DDRP's tend to have a problem with cold temperatures.

 

I am new to this COLD weather, was 55 this morning when I left, should be a cool 80* today.  

2 hours ago, portlandareae28 said:

 

I am new to this COLD weather, was 55 this morning when I left, should be a cool 80* today.  

 

Not even cold yet. 55*F in the morning is a typical summer morning for me.

 

Cold is when you start diving below 0*F now that's cold now you should consider using the block heater. Right around 32*F I start using grid heaters on the first start of the day. I don't even worry about plugging in the block heater till it diving below ZERO. Sad, part is when I'm traveling I don't have an option to plug in if it below zero. I just cycle the grid heaters twice and fire up and let it warm up for just a bit. This is why I don't panic about plugging in because once I travel somewhere there is no way to plug in again. Why worry...

Edited November 5, 20186 yr by Mopar1973Man

I doubt I will see much below 32* maybe once in a blue moon, I will never see 0* here in Southern California.   Now that I am moved and somewhat settled in through, it is time for the truck to get some needed attention.  

Then there is nothing to worry about. You don't even have to worry about change oil up for the extreme cold.

 

Personally, myself we do get minus weather at least once a winter but I typically don't sweat it because the first part the truck is parked in a unheated shop for the night typically around 40*F through the winter. Then sub-zero typically for us only last a few days to a week or so. Not worth going into panic mode. I pay attention to the logging companies and I've got friends that work the shops so I typically get heads up of temperature related issues. 

I just did a search on the DDRP lift pumps. Unbelievable bad reviews about it on Amazon. Not only is there no regulator but they have had some failures, one in as little as 2,000 miles. One guy got an empty box sent to him when he ordered one and then the company never sent another shipment like they said and no response from the company until the guy finally gave up. Another had a failure in 10k miles.

 

Your lift pump may be failing based on what I just read. I would be going for a different brand L/P with the proper relay wire harness and big line kit included. Vulcan performance parts can set you up with the whole kit. If Eric is going to wholesale only he can still send you in the right direction to get his kit. I have them on both my trucks.

Edited November 6, 20186 yr by JAG1