Hey guys, new here and this is my first post. Recently replaced the fuel pump in my 91 3.0. Ran fine for a couple of weeks. Now it seems to stumble a little bit under load, going thru the gears. It's a manual transmission. Today I replaced the fuel filter and the problem remains. It idles just fine, maybe a tad high. I have sprayed carb cleaner around in the engine to check for vacuum leaks, and don't seem to have any. The fuel pump I replaced it with is from Rockauto, and the specs say that the max fuel pressure is 70psi, and the min is 60psi. My question is, is that too much psi? I haven't checked fuel pressure at the engine yet, I haven't sourced one of those banjo bolt tester fittings yet.

Just kinda asking for suggestions at what I should check next. I have found a testing procedure for the TPS, and I'm fairly comfortable doing that, but just don't know if it's necessary. Anyway, thanks in advance.

 

Oh yeah, forgot to mention, I don't have any engine codes

 

When you say it stumbles under load, is that at all RPM? If it's near the top of the range (with the pedal to the floor) I could see it being a fuel pump pressure/volume problem. If it's at lower RPM under variable throttle, maybe something else? Other culprits might be bad or partly plugger injectors or maybe an aging ignition coil or cracked plug wires?

Good luck!

 

It isn't all RPMs. And I have yet to change plugs, wires or the like. But like I said, it ran fine, fuel pump died, replaced that. And it ran fine after that for a couple of weeks. I was wondering about fuel pressure because the pump I put in it has a minimum 60 psi. I was wondering if that was causing the flutter/stumble the more throttle I give it. Also, while it's sitting still, idling, I can give it full throttle and it never skips. Just when it's moving

 

IIRC the 3.0 only needs 38-44 psi of fuel pressure, but anything over that it just returned to the tank unless the fuel pressure regulator is failing too.

 

As rattlewagon says, the fuel pressure in the rail is set by the Fuel Pressure regulator. Any pressure "over" what it wants is just returned to the tank (so the pump has to always put out more than the minimum rail pressure needed). Note that the rail pressure goes up and down to track the manifold pressure. As you open the throttle, increasing the pressure in the manifold (or, reducing the vacuum), the FPR increases the rail pressure so that the injectors always see the same pressure across them.

So replacing the pump doesn't affect rail pressure, unless the pump is so weak it can't reach the minimum needed.

 

Was able to put a guage on it today. Fuel pressure was staying at a pretty steady 48psi. So, I suppose I need to look at the next step. I don't know when the last time plugs, wires and distributor cap was replaced.

Also noticed today, that when the flutter starts, I can ease up on the throttle, and it levels out. Just wondering if going thru that TPS test might bear something fruitful.

I reckon if the tune up don't help, maybe a look at the injectors may be in order

 

A couple of things I like to do if I’m having an intermittent running issue is check both timing and the TPS. They’re both easy and cost nothing(unless you don’t have a timing light, but you need a timing light). At minimum you want to verify the TPS is registering the IDL signal with a closed throttle and that the throttle is actually closed for that matter. Once you confirm those things, it’s easy enough to move down the list of troubleshooting.

 

I've watched a couple videos on checking the TPS. Doesn't look too hard to check. Removing it looked to be the easiest as well. Or at least to me.

 

You don’t necessarily have to remove the TPS or the harness to check it. Just as you would do to set timing or check for fault codes, stick your paperclip between TE/E1 and check your CEL in the cab for rapid flashing once the truck is running. If it’s rapid flashing, you’re on IDL and the TPS “works.” If it’s slowly flashing blinking out a numerical code, you’re not on IDL (Code 51) or there’s other fault codes registering.

 

Thanks for that info. I don't have any codes flashing with the ignition in the on position.

So I need to jumper those 2 pins out and crank it? To test the TPS?

 

OK thanks to mholme. I jumpered the pins, and started the engine. Got the code 51. So does that mean my TPS is bad? Or just needs adjusting?

 

Try to physically move the throttle butterfly closed with your hand before you start messing with the TPS. They can hang up on the cable or even gunk in the throttle body. If you can’t close it any further with your hand and you’re still off IDL, you need to look at setting it properly. At that point you, you probably are best tearing it down a little further if you have unknown maintenance history(inspect/clean the throttled body). One step at a time though. Get your TPS to do what it’s supposed to, when it’s supposed to.

 

OK, I got the steady blinking light at startup. But when I touch the throttle, the 51 comes back until the throttle closes. If I'm gonna take the throttle body off for a good cleaning, I have a couple of questions.

Read the write up on setting the TPS with a timing light. I have the V6 engine, and was wondering what base timing for that engine is. Next question, if I'm gonna have the throttle body off, does anybody know the length and thread pitch of the screws that hold the TPS in place is. Gonna try and clean the throttle body as good as I can before I remove the TPS. I've heard those adjusting screws are not fun and would rather just change them to Allen heads.

Also wanna thank you guys for answering my questions with the information I'm giving. I know some forums I've been to, folks are quick to throw the "use the search function" reply out there. And by the way, I am using it.......lol

 

Code 51 pops up whenever you are off IDL, like when you rev the engine. It should go away when the throttle closes completely, and you’ll get rapid flashing, indicating you are back on IDL. So if that’s the case, the TPS is doing its thing correctly as far as the IDL switch is concerned.

 

I was able to put a timing light on it. Seems to be @ 10* with the pins jumpered and the idle between 800 and 900 rpm.. Couldn’t get a solid answer in the FSM. Is that right? Seems like I seen 8* in there too. Also have plugs, wires and cap on the way.

 

The FSM definitively specifies 10 degrees with terminals jumped and further check that timing advances to 8 degrees, with the jumper removed.

 

Ok, I was a little bit confused on that. Thanks for the clarification

 

It confused me too, since it says check that the ignition timing “advances” to 8 degrees with the jumper removed. Just make sure you’re in diagnostic mode(jumper wire in, CEL rapid flashing) and you see 10 degrees with your timing light. When you pull the jumper, you should see 8 degrees.

 

I think something that never happens to me, has happened. The most obvious and simplest fix has it purring again. Replaced the spark plugs, wires, cap and button today, and it seems to have gotten it. Fingers are crossed anyway