So I spend a good part of the day putting in a Fuel pressure Gauge today. It's cold out! Did my research and read many peoples thoughts on Isolators. Decided to go with an Isolator. Spent the extra Bucks at Deisel Manor. Decided on a steering collum pod. Cautiously filed the isolator and plastic tube to the guage (Pain in the EDIT) cracked the scew on the Isolator till diesel flowed. But despite all my due diligence the gauge fluxuates up and down from 4 pounds to 15 pounds with no ryme or reason. Sometimes it works like I would expect it to (15 pounds at Idle and 7 under power) other times it drops to 4 pounds and stays there or goes to 15 pounds under power.

So I have decide to give it a week to sort itself out (Air in the lines?) and if I still have the same readings I will loose the Isolator. The of it all is I don't know if the guage is actually working right and I have a LIFT PUMP GOING OUT or if the isolator is just buggy. Should have gone without the isolator from the start Demm da Berries

 

Good move on the isolator IMHO.

When I put my gauges in (first Bomb) everything was great. The next morning, fired it up, FP = 14psi. By the time I hit the end of my driveway, FP = 5! I thought it was the gauge, wrong, I had just lost my first LP.

If you end up needing a new LP, consider relocating it to the frame rail in front of the tank. Check out the Vulcan Big Line Kit. Better pressure, less heat and vibration on the LP and more fuel volume.

Vulcans kit makes it all easy, less $ too.

 

Isolators can be bad out of the box. But, maybe the lift pump is bad as well. That's the fluctions my last factory LP did before dying.

You could verify with another gauge just to be sure though.

Dave

 

I had the same problem with the same gauge. Ended up tossing the isolator and running fuel right to the gauge with the shutoff valve on the IP. Works great now, rock steady FP values.

 

you need to hook your mechanical gauge up direct and test under the hood if you feel better that way. I first hooked up and temp air cond. hose and a 0-15 gauge to the filter and drove with the gauge poped out the hood in the wind shield and found that the pump was going out, went from 10.5 to 5.5 randomly and then more often parked till I got a Air dog installed and now have a digital summit pressure gauge and a mechanical on tee'd off the sending unit with a ball valve snubber.

 

When installing an isolator the diaphragm should be depressed toward the fuel side, the isolator and tube should both be filled getting out as much air as possible. The pipe threads should be sealed with a good diesel compatible sealant, we use Loctite 545, the compression fittings should be tightened about a 1/2 turn past resistance, too tight and it could pinch causing the tubing to leak. Bleed the fuel side and you should be good.

The pressure fluctuations your having do sound like a bad pump, when I sold Carters we did have some bad right out of the box, nuff said about that. But double check the pressure like Ed mentioned with a direct mechanical gauge.

Ed has a good setup with that sending unit keeping it off the engine and having that back up mech gauge, thats the way I used to run my electric gauge.

E

 

Well I waited a week to see if things would sort themselves out. Still had the random fluxuations in the gauge. So I went to the speed shop and got a copper line and got rid of the isolator. I got the same readings but alot faster. Instead of slowley floating up and down I got quick movements up and down. Down to 2 then up to 15 and back. So I went to a few places looking for an airtex lift pump. Auto zone did not know what a lift pump was and wanted to sell me an injector pump. Treated me like an idiot I ended up a Napa Auto and they had a Carter, (No AirTex). I put it in (two hours not bad, with a new fuel fiter) and the problem is solved. For now

Anyway, I ve had the truck 3 weeks and thanks to you all I have fixed my TC lock up, put in a fuel pressure gauge and now installed a lift pump. I know it seems silly but it feels good to wrench on my own truck. Never had enough elbow room on my toyota. I was beginning to think I had gotten to old

 

I had rapid needle movement, but steady readings with my Autometer gauge & several different lift pump setups. The gauge line is 1/4 " hydraulic hose w/ flare fittings & is tee'd into the high press. line coming out of the fuel filter, no isolator. I was able to eliminate the needle fluctuations by running the gauge line with a loop to trap some air, above the level of the point of connection.
daveg.