Engine/Transmission (1994 - 1998) Help with fuel pressure fluctuation

[lkuykendall]

My post filter fuel pressure has started jumping back and forth from 10 to 20 pounds while driving. It jumps some at idle but it is worse from 1500 rpm up. My fuel filter was new but I changed it to eliminate it as a possible cause. I would appreciate anyone's suggestions or ideas on this. I am supposed to leave on a 1500 mile trip pulling a heavy load on Friday and would like to have this corrected.



This is on a 1996 3500, 5spd 167,000 miles with a new mechanical Isspro fuel pressure gauge.



Thanks



Len

 

[illflem]

I think the problem is the gauge setup. Does it have a snubber or valve to restrict the line to the gauge? If it doesn't the gauge won't last long jumping around and you'll never get a correct reading. If it has a valve for a restrictor it may need to be closed down a little more. Sometimes air in the line to the gauge will act as a cushion to prevent the pulses when first installed but will eventually fill with fuel and start pulsing. The overflow valve doesn't usually cause pulsing when it fails, the lift pump can. The injection pump can also feed back pressure spikes to the gauge.

 

[lkuykendall]

Thanks for the reply illflem.

I don't have a valve in the fuel line going to the gauge. I will look into adding one. I don't want to damage the gauge but more importantly, I want to verify that the lift pump etc. . are ok.

Thanks again.



Len

 

[lkuykendall]

I just wanted to post a follow up in case anyone else runs into this problem. Illflem was exactly right in his post. Once I restricted the flow going to the gauge, all fluctuation stopped. Once again TDR saves the day!!!

Thanks again Illflem!



Len

 

[illflem]

You're welcome. Many times 24 valves can get away without a restrictor, not always though, they're cheap enough that they should have one anyway. 12 valves always need the restrictor. Sometimes an unrestricted gauge won't pulse but will make an irritating buzz. Some electrical gauge senders won't let you see the pulsations while they are ruining the sender, the pulsations are there though hammering away.