Fuel System Issue

[grntRUDD13]

I'll just start by describing the problem when it first appeared, and then tell what a little bit of diagnosing found because I don't know what the problem would be, or what would cause it. So, I was driving the SVO (86, stock engine except for TC intercooler, and drop in K&N Filter element) and was almost home when my SVO started bucking, not just under load, but idle or otherwise. It wasn't backfiring, but was sputtering like it was running out of gas, or wasn't getting any gas. It would run for a second and then the rpms would drop, and this process would continually repeat itself. I was able to coast/feather the throttle and clutch to get it within sight of my house before it died and wouldn't start. The things I noticed were that it wasn't backfiring, you couldn't smell gas, and the exhaust temps were sky high (it started to melt the underbody coating). To me this seems like a lean condition mostly because of the exhaust temps and no backfiring. When my brother (the previous owner) came to help, by tapping on what we found was the "fuel pressure damper', it would at least start and run. It is getting gas at least up to that point so the pumps are working, and the filter isn't clogged. What does the fuel pressure damper do, and why would it make the engine not run? If that is the problem, if not, what do you all think the problem might be? If you need more info, just ask and I'll try to answer any questions.

Thanks,

Grant

[MikeFleming]

My first thought from your description is that your battery is undercharged - same symptoms when the alternator dies: loss of power, sputtering, etc. So get a voltmeter on that battery first.

If that's OK, then get a fuel pressure gauge on it and see what is happening there.

[grntRUDD13]

It still cranks over just fine. Not slow or anything like that. Wouldn't an undercharged battery have issues cranking? I'll have to put a fuel pressure guage on it to see if the pressure is low or whatnot.

[grntRUDD13]

So I got a fuel pressure guage and checked the fuel pressure at the rail, and got a big fat zero. This was with the ignition on, and also attempting to start the car. I checked the line leading to the fuel pressure damper (I still have no idea what this does so if anyone can enlighten me, I'd be grateful.) and there was pressure to it, but not at the rail. You can clearly hear the fuel pump so between that and pressure in the lines, I'd assume that it is working. This all goes along with the lean condition assumption, and also makes me think the problem might be the damper. I may be wrong, but I always thought that if the fuel pressure regulator went bad, then the pressure would be high. I also checked the battery with a voltmeter, and it checked out fine. Am I on the right track with this damper thing and should order a new part? Or is it something completely different? Thank you.

[rickibrat2]

So I got a fuel pressure guage and checked the fuel pressure at the rail, and got a big fat zero. This was with the ignition on, and also attempting to start the car. I checked the line leading to the fuel pressure damper (I still have no idea what this does so if anyone can enlighten me, I'd be grateful.) and there was pressure to it, but not at the rail. You can clearly hear the fuel pump so between that and pressure in the lines, I'd assume that it is working. This all goes along with the lean condition assumption, and also makes me think the problem might be the damper. I may be wrong, but I always thought that if the fuel pressure regulator went bad, then the pressure would be high. I also checked the battery with a voltmeter, and it checked out fine. Am I on the right track with this damper thing and should order a new part? Or is it something completely different? Thank you.

check fuel filter and replace my other mustang it was infront of rear alxe attaced to floor board not sure where they are on the svo

[Bob Holmes]

The fuel pump and injectors create a pulsing fuel supply, much like getting "water hammer" in your home water supply. The damper is there to quell the pulse.

[grntRUDD13]

Ah. That makes sense, keeping the fuel going to the regulator at a constant volume and pressure. When it goes bad, would it keep pressure from getting to the fuel rail? There is pressure at least getting to the back side of the damper, but at the fuel rail, there is none. Is that common with a damper failure?

Thanks

[Stinger]

Ah. That makes sense, keeping the fuel going to the regulator at a constant volume and pressure. When it goes bad, would it keep pressure from getting to the fuel rail? There is pressure at least getting to the back side of the damper, but at the fuel rail, there is none. Is that common with a damper failure?

Thanks

I've never personally seen a damper fail but they are easy to bypass to test for a failure. Since yours does seem to be the problem, just remove the damper and connect the fuel line directly to the rail.

[MikeFleming]

... just remove the damper and connect the fuel line directly to the rail. +1

My 84 has been driven 170,000+ miles without a damper in place. Fortunately the hose connectors are the same and the hose is long enough.

[grntRUDD13]

So, I finally found the problem. Or problems... Turns out that not only was the fuel pressure damper bad, causing the rail to get zero pressure, the fuel pressure regulator was also bad. Go figure, both go bad at the same time. Runs great now. Downside is that the engine compartment ate my schrader adapter for my fuel pressure checker, and I now need new 4mm allen wrenches, and a 4mm socket. They are now permanently together. In hindsight, probably wasn't the best idea to CA glue the trimmed off allen wrench to a good socket. Should have used one of the cheapie chinese ones instead. The good news is that now it runs, and I can buy new adapters, allen wrenches, and sockets individually. Hopefully changing the front brake pads goes smoother...

[MikeFleming]

"Tool Sacrifice" - see "Virgin Sacrifice".

Yeah - just get more tools.

Nice Job! Good to hear it's running again!