Fuel Pressure Regulator question

[eagle23]

I have a 1991 Ford Ranger, 3.0 Vulcan V6. 86k original miles.

I suspected the fuel pressure was off, especially for idle right after hot start up. Got a fuel pressure gauge on the tool loaner program at AZ.

The pump seems to test fine; factory specs the range of pressure at 35-45psi.

With the regulator connected via its vacuum line, it's about 32 psi but goes up when the engine is revved. That would suggest the idle problem.

If I leave the vac line off, fuel pressure is a steady 40psi, idle or high revs. Idle is better.

My question: is there a reason to replace the regulator, or is there something I'm missing? It's a bit of a pain to do (can get to only 2 of the 3 screws easily).

Is there any harm to just running without it's being connected, and just plugging the vacuum line?

TIA

 

[morris]

could it be that when you ask for power the pump cant keep up?

 

[yonyon]

Normal operation involves this behaviour: open the throttle -> reduced vacuum to regulator -> instant power enrich effect. With the vacuum disconnected that's the same as WOT: max fuel pressure.

You're getting that effect, but with lower pressure readings so it could be a bad gauge as easily as a bad regulator. Loaner tools from a tool store don't always lead easy lives. It might be worthwhile to see what that gauge reads on a vehicle that you know runs well and then condemn the regulator.

 

[yonyon]

My handy dandy pocket reference is showing me that your 35 to 45 psi. spec. is for engine off which I assume should be the same as vaccuum line disconnected.

Engine running shows 30-40 psi. 32 fits into 30-40.

Edit:
While you have that fuel pressure gauge handy, see if your fuel pressure slowly drops while sitting with the engine off. That would be typical of a leaky fuel pump or injector. A leaky injector would certainly tend to cause a rough idle after warm start

Second edit:
This is BITOG so, um, do you have a used oil analysis? If you do have one just go ahead and whip it out. It might show something useful.

 

[yonyon]

Please excuse me for my usual spouting off with a bunch of words that weren't an answer to your question. I do that.

Running with the vacuum line to the regulator capped off shouldn't "hurt anything" much, really, but should cause a bit of a hesitation when you hit the gas. Fuel economy and emissions could take a slight hit but not enough to matter.

 

[eagle23]

That isn't the symptom. WOT has good response. The idle is a bit off, but more it's really lumpy when first started hot.

 

[another Todd]

My silverado had hot start problems. The fuel regulator was bad and the vacuum line was sucking fuel into the manifold. Replaced the regulator and that cured it. I did notice some black smoke when hot starting it, that was a clue.

 

[eagle23]

Originally Posted By: yonyon
Normal operation involves this behaviour: open the throttle -> reduced vacuum to regulator -> instant power enrich effect. With the vacuum disconnected that's the same as WOT: max fuel pressure.

You're getting that effect, but with lower pressure readings so it could be a bad gauge as easily as a bad regulator. Loaner tools from a tool store don't always lead easy lives. It might be worthwhile to see what that gauge reads on a vehicle that you know runs well and then condemn the regulator.


Thanks for explaining the regulator process using vacuum. I hadn't really understood it.

I know what you mean about loaner tools. In this case the gauge set looked virtually new. Even the molded plastic box it came in had no scuffs or signs of wear. For that reason, I'm incined to take the #'s as valid.

Since I don't have a vehicle set up like that, I decided to spring for the $16 for the regulator at AAP, after the online discount. In the next week or so I'll replace it. Even if I'm wrong I'm not out much.

You made a comment, though, that might relate to the rough idle. I understand these engines can have a lean misfire at idle. I've noticed that when the AC compressor kicks in, the idle tends to get smoother, leading me to think the ECU sends a signal to richen the idle mixture slightly to compensate for the compressor's running. Or at least that makes sense from here

 

[eagle23]

Originally Posted By: yonyon
My handy dandy pocket reference is showing me that your 35 to 45 psi. spec. is for engine off which I assume should be the same as vaccuum line disconnected.

Engine running shows 30-40 psi. 32 fits into 30-40.

Edit:
While you have that fuel pressure gauge handy, see if your fuel pressure slowly drops while sitting with the engine off. That would be typical of a leaky fuel pump or injector. A leaky injector would certainly tend to cause a rough idle after warm start


Second edit:
This is BITOG so, um, do you have a used oil analysis? If you do have one just go ahead and whip it out. It might show something useful.


The pressure held for at least 10 minutes with the engine off, at ~40psi. The 32psi struck as within range, but at the lower end of acceptable so I don't rule it out as a reason the idle is as it is. The injectors are all reman, within the past year or so. It didn't show any signs of injector leak-down.

Despite being a member of BITOG for several years I've never had a used oil analysis done

 

[eagle23]

Originally Posted By: yonyon
Please excuse me for my usual spouting off with a bunch of words that weren't an answer to your question. I do that.

Running with the vacuum line to the regulator capped off shouldn't "hurt anything" much, really, but should cause a bit of a hesitation when you hit the gas. Fuel economy and emissions could take a slight hit but not enough to matter.


No harm done at all. I much appreciate your thinking about this, very much so.

 

[eagle23]

Originally Posted By: another Todd
My silverado had hot start problems. The fuel regulator was bad and the vacuum line was sucking fuel into the manifold. Replaced the regulator and that cured it. I did notice some black smoke when hot starting it, that was a clue.


As in another reply, I decided to go for the regulator anyway as it isn't expensive. Your reply helps confirm the direction I'm headed, so thanks. Even though that regulator isn't more than 3-4 yr old, I know they can go bad regardless of miles/age.

I may also replace the fuel filter even though the one on there has <20k on it. I have one on the shelf so may as well use it.

 

[yonyon]

Suspected lean miss at idle in a Ford hmm.... Here's a few questions:

-Do you have access to a scan tool that will show live data such as fuel trims? I'm going to assume "no" at this point ue the the age of the vehicle.
-Are you okay with pulling the spark plugs and taking pictures or looking at them and comparing to pictures?
-Have you already checked (both visually and also using fingers with your eyes closed) for rubber vaccum hoses and elbows that have collapsed and made holes?

Those older Fords like to develop vacuum leaks and idle lean, but to misfire from it (unless the plugs are crazy worn) and feel rough is unusual. Typically that would be a leaking intake gasket (usually only w/ a plastic intake and I think you have aluminum) or an EGR valve that doesn't close fully. If it were an EGR valve it would be intermittent. If it were an intake gasket it should be worse after a cold start than a warm start. Still... a vacuum leak would jive with feeling smoother with the AC on.

Run some injector cleaner through there. It's a couple of extra bucks to spend when you pick up your fuel pressure regulator. You'll find lots of info about specific fuel injector cleaner products that have PEA in them searching BITOG. A dirty injector would make an individual cylinder run leaner than the rest. The problem would be masked on a cold start because the ECM is commanding extra rich for the low temperature.

 

[mechtech2]

Originally Posted By: yonyon
Please excuse me for my usual spouting off with a bunch of words that weren't an answer to your question. I do that.

Running with the vacuum line to the regulator capped off shouldn't "hurt anything" much, really, but should cause a bit of a hesitation when you hit the gas. Fuel economy and emissions could take a slight hit but not enough to matter.

This is backwards. Less hesitation should result with the richer mixture, and fuel economy will take a bigger hit.

 

[yonyon]

Originally Posted By: mechtech2

This is backwards. Less hesitation should result with the richer mixture, and fuel economy will take a bigger hit.


I haven't tried actually driving around like that but would expect the mixture to stabilise the same with the hose on/off due to O2 feedback. I was thinking that without the instant extra fuel when quickly opening the throttle that would give it a hesitation.

You're probably right. If it's already running lean because something is wrong, that extra fuel pressure should make it less lean and just plain run better.

 

[eagle23]

Originally Posted By: yonyon
Suspected lean miss at idle in a Ford hmm.... Here's a few questions:

-Do you have access to a scan tool that will show live data such as fuel trims? I'm going to assume "no" at this point ue the the age of the vehicle.
-Are you okay with pulling the spark plugs and taking pictures or looking at them and comparing to pictures?
-Have you already checked (both visually and also using fingers with your eyes closed) for rubber vaccum hoses and elbows that have collapsed and made holes?

Those older Fords like to develop vacuum leaks and idle lean, but to misfire from it (unless the plugs are crazy worn) and feel rough is unusual. Typically that would be a leaking intake gasket (usually only w/ a plastic intake and I think you have aluminum) or an EGR valve that doesn't close fully. If it were an EGR valve it would be intermittent. If it were an intake gasket it should be worse after a cold start than a warm start. Still... a vacuum leak would jive with feeling smoother with the AC on.

Run some injector cleaner through there. It's a couple of extra bucks to spend when you pick up your fuel pressure regulator. You'll find lots of info about specific fuel injector cleaner products that have PEA in them searching BITOG. A dirty injector would make an individual cylinder run leaner than the rest. The problem would be masked on a cold start because the ECM is commanding extra rich for the low temperature.


I doubt it's an injector but there's zero harm in runningsome good PEA cleaner. I'll probably go with Redline SI-1.

The vac hoses aren't but maybe 4-5 yr old but are cheap enough to replace, so I'll do that too. It may well be one of these small things that are the culprit and I just haven't located it yet.

The intake is aluminum, you're right. I had it off and apart middle of last year when I redid the lower manifold gasket which was leaking oil. I made sure to put a thin skim of permatex on the upper gasket as well to help seal both sides, before cleaning well the mating surfaces.

The plugs are <1000 miles. That was my first suspicion, to the point that over the years I went to colder ones. I'm now using Denso iridiums for easier firing. The autolites I took out looked fine, and the idle was unchanged either way.

 

[eagle23]

Originally Posted By: yonyon
Suspected lean miss at idle in a Ford hmm.... Here's a few questions:

-Do you have access to a scan tool that will show live data such as fuel trims? I'm going to assume "no" at this point ue the the age of the vehicle.
-Are you okay with pulling the spark plugs and taking pictures or looking at them and comparing to pictures?
-Have you already checked (both visually and also using fingers with your eyes closed) for rubber vaccum hoses and elbows that have collapsed and made holes?

Those older Fords like to develop vacuum leaks and idle lean, but to misfire from it (unless the plugs are crazy worn) and feel rough is unusual. Typically that would be a leaking intake gasket (usually only w/ a plastic intake and I think you have aluminum) or an EGR valve that doesn't close fully. If it were an EGR valve it would be intermittent. If it were an intake gasket it should be worse after a cold start than a warm start. Still... a vacuum leak would jive with feeling smoother with the AC on.

Run some injector cleaner through there. It's a couple of extra bucks to spend when you pick up your fuel pressure regulator. You'll find lots of info about specific fuel injector cleaner products that have PEA in them searching BITOG. A dirty injector would make an individual cylinder run leaner than the rest. The problem would be masked on a cold start because the ECM is commanding extra rich for the low temperature.


I doubt it's an injector but there's zero harm in runningsome good PEA cleaner. I'll probably go with Redline SI-1.

The vac hoses aren't but maybe 4-5 yr old but are cheap enough to replace, so I'll do that too. It may well be one of these small things that are the culprit and I just haven't located it yet.

The intake is aluminum, you're right. I had it off and apart middle of last year when I redid the lower manifold gasket which was leaking oil. I made sure to put a thin skim of permatex on the upper gasket as well to help seal both sides, before cleaning well the mating surfaces.

The plugs are <1000 miles. That was my first suspicion, to the point that over the years I went to colder ones. I'm now using Denso iridiums for easier firing. The autolites I took out looked fine, and the idle was unchanged either way.