Most questions here are to fix a problem - or - "Why is it broken?" I want to know "Why is it fixed?" <img src="/forums/images/graemlins/lol.gif" alt="" />

Ever since I installed my present engine, I have occasionally gotten a whiff of gasoline vapor, but I've never found a leak. Lately, the engine has run a little ragged at times when it was cold - seemingly lean - but after a few seconds of power, it smoothed out, so I didn't worry about retuning it yet.

Last week, I changed the oil and while the engine was running, gave a look 'round the engine bay for any potential problems and found this:



After my shock that the gauge was pegged and the thought that I was probably washing the cylinders with gasoline and ruining the engine, I calmed down and realized that it wouldn't be running at all with that much fuel pressure. Besides, I had just changed the oil and it didn't smell gassy. So, I accepted that the gauge had blown and ordered another one from Summit.

The new gauge arrived a few days ago and I installed it Thursday - all is fine....... finer than I figured it would be. <img src="/forums/images/graemlins/scared.gif" alt="" />

Some of you will remember that I have been complaining about the torque converter lockup that makes the truck bog in O/D at low rpm with seemingly not enough engine torque to easily pull out of the hole in O/D around 1800rpm without downshifting. That is no longer true - nor is the ragged running when cold as bad as it was. The transmission now shifts when I expect it to shift and there is smooth power all across the band. <img src="/forums/images/graemlins/confused.gif" alt="" />

I guess I shouldn't complain, but I'd sure like to understand what has happened. I can't detect a leak in the old gauge in either direction. The weather is a bit warmer, but I don't think that has anything to do with it. Something magical has happened and I haven't yet figured it out.

Any SWAG is welcomed. <img src="/forums/images/graemlins/lol.gif" alt="" />

Frank

I vote that you reseated / bumped some electrical connections around the distributor, and are now getting complete spark.

Monteros and Raiders sometimes just like to be stroked. Girl cars like shiny new parts. <img src="/forums/images/graemlins/pfft.gif" alt="" />

The bad gauge was acting as a "capacitor" in the fuel circuit allowing pressure to drop momentarily during highest point of fuel demand..(yea a long shot I know).

OR maybe the gauge nipple was screwed into the line too far causing a restriction in the line?

I think that your gauge has a minor leak which would allow air to enter your fuel rail i.e. when engine is cooling down. Now that you have a sealed system, everything runs the way it was intended it to.

The pegged gauge could be due to fuel vaporizing within the fuel rail when engine is really hot and not running therby raising the pressure . for the same reason.

Did you also experience difficult starting when engine warm/hot?

Qurious what you find.

Love it!! <img src="/forums/images/graemlins/smile.gif" alt="" />

That's a bourdon tube gauge, a coiled tube "unwinds" some under pressure, moving the needle thru a linkage. If no leaks in the tube, it is incidental that changing it changed the engine running. The gauge is sprung from too much pressure on the bourdon tube permanently distorting it. Let's examine why. Either the gauge had an internal defect/weak spot, or the gauge saw a heavy pressure spike. The source of a spike is logically the fpr.

One, where exactly in the fuel system is the gauge?

Two, does the gauge remain stable at all running regimes?

To address some of the above, the only way you could suck air into the system is for the fuel pressure to drop below ambient, which will only happen if the fpr leaks down residual system pressure AND the fuel has vapor bubbles in it that recondense on cool down, causing a negative pressure, but I think the vapor pressure would increase as vac increases. In any case, the positive fuel pressure when running is a lot higher than the suction pressure possible in the line, so you'd see a leak under pressure before you'd get air sucked in.

I sort of tend to the obstruction in the line idea..

The gauge screws directly into the side of the Holley fuel pressure regulator:





Thread sealant used on installation - no teflon tape to clog up the works.

Frank

I thought this was not about Mitsu-porn. Darn!

On my Raider TBI there is a pulsation damper to remove the pressure spikes from both the injectors firing and from the pump.

My system actually has two, one on the pump and one on the throttle body.

It is possible that the gauge acts as a pressure damper? The tube inside does increase in volume with pressure and a tube that gronked may not work as well.

How much pressure surge you get can also depend on the pump type. The vane pumps supposedly have a smoother output than the other. I know mine makes more noise.

Or a weird coincidence.