Poor Idle and no acceleration

[adgalloway]

Hey all,

I'm hoping someone can help me get on the right track in diagnosing the issues with my dad's 1999 Ford Explorer V6 4x4. On a cold start the engine takes a long time to fire up. Once it does it is prone to stalling and won't idle without throttle input until the engine is warm. The CEL is on, and I've attached a scan PDF of all the codes. It also doesn't have much power when accelerating and seems to bog down and not run strong.

 

[J_C]

You're running lean on both banks, wrong fuel air mix whether it is from too much unmetered air getting in, or not enough fuel.

Unmetered air, you could try cleaning the MAF sensor but it's probably a vac leak somewhere. Check the vac hoses but it could be the intake manifold gasket leaking.

Which engine? 4.0L OHV V6, 4.0L SOHC V6, or 5.0L OHV V8?

Not enough fuel, you can hook a fuel pressure gauge up to the fuel rail. Autozone and others will lend those as a free loaner tool (deposit required). AFAIK, all 3 engines switched to the returnless fuel system in '99 which should have roughly ~60PSI. I could be wrong.

 

[adgalloway]

It appears to be 4L SOHC.

 

[adgalloway]

You're running lean on both banks, wrong fuel air mix whether it is from too much unmetered air getting in, or not enough fuel.

Unmetered air, you could try cleaning the MAF sensor but it's probably a vac leak somewhere. Check the vac hoses but it could be the intake manifold gasket leaking.

Which engine? 4.0L OHV V6, 4.0L SOHC V6, or 5.0L OHV V8?

Not enough fuel, you can hook a fuel pressure gauge up to the fuel rail. Autozone and others will lend those as a free loaner tool (deposit required). AFAIK, all 3 engines switched to the returnless fuel system in '99 which should have roughly ~60PSI. I could be wrong.

So it is a SOHC 4.0L I tested for vacuum leaks by spraying ether on all vacuum hoses and connections that I could locate. I didn't notice any change in idle speed. Also inspected all those hoses for cracks or deterioration. IS there a more concrete way to check for vacuum leaks? I do have a vacuum gauge I use mostly to sort out carburetor issues on old chevy V-8's, but I'm not sure where best to connect it on this engine or what normal engine vacuum should read.

I'm going to see if I can get a fuel pressure gauge today to connect to the fuel rail shrader valve. I'm hoping to see 60 PSI

Also, is it likely that an o2 sensor could be causing this issue or a clogged catalytic converter?

Thanks,

 

[J_C]

If you have to give it more throttle to get it to idle, it's not a clogged cat. Vac leak or fuel pressure is far more likely than an O2 sensor.

 

[adgalloway]

If you have to give it more throttle to get it to idle, it's not a clogged cat. Vac leak or fuel pressure is far more likely than an O2 sensor.

Thank you,

I got a chance to pressure test the fuel rail today. Here is what happened:

Connected gauge and turned key to run, pressure came up to about 5-7 PSI.

Attempted to start the car, pressure began to rise and topped out at 25 PSI. I let it idle for a couple of minutes.

I shut off the engine, pressure dropped back to zero almost instantly.

Bad fuel pump? Check valve somewhere?

 

[J_C]

Yes that fuel pressure is too low, pump and/or filter. I'd start with the pump but plan on the filter too unless you have a situation where the fuel pressure gets back up where it should be but the fuel line at the filter is so rusted that you don't dare touch it. That may be less of a problem in GA since you don't have so many salted winter roads. The filter really should be changed at this age unless it was done already in recent years... some people buy cheap generic fuel pumps and who knows how many times they do this repair after ~22 years and/or potentially multiple owners. I tend to assume too often that everything on a vehicle this age is original when it may not be.

I suppose you could try replacing just the filter first, but if the pump is the original it is aging out and due to fail. The fact that the pressure dropped down so fast when shut off, also suggests the pump rather than filter.

Now I have reached a limit to my understanding of the '99 fuel pressure regulation. It may be that the pump alone is not enough, that you need the whole sending unit with its integral pressure regulator? Someone else will have to advise about this, without further info I would get a whole new sending unit, aka "Fuel Pump & Housing Assembly" on Rock Auto. The check valve/pressure regulator is part of that sending unit rather than the pump itself AFAIK.

1999 FORD EXPLORER 4.0L V6 SOHC Fuel Pump & Housing Assembly | RockAuto

RockAuto ships auto parts and body parts from over 300 manufacturers to customers' doors worldwide, all at warehouse prices. Easy to use parts catalog.

www.rockauto.com

 

[adgalloway]

Yes that fuel pressure is too low, pump and/or filter. I'd start with the pump but plan on the filter too unless you have a situation where the fuel pressure gets back up where it should be but the fuel line at the filter is so rusted that you don't dare touch it. That may be less of a problem in GA since you don't have so many salted winter roads. The filter really should be changed at this age unless it was done already in recent years... some people buy cheap generic fuel pumps and who knows how many times they do this repair after ~22 years and/or potentially multiple owners. I tend to assume too often that everything on a vehicle this age is original when it may not be.

I suppose you could try replacing just the filter first, but if the pump is the original it is aging out and due to fail. The fact that the pressure dropped down so fast when shut off, also suggests the pump rather than filter.

Now I have reached a limit to my understanding of the '99 fuel pressure regulation. It may be that the pump alone is not enough, that you need the whole sending unit with its integral pressure regulator? Someone else will have to advise about this, without further info I would get a whole new sending unit, aka "Fuel Pump & Housing Assembly" on Rock Auto. The check valve/pressure regulator is part of that sending unit rather than the pump itself AFAIK.

http://[URL]https://www.rockauto.co...fuel+&+air,fuel+pump+&+housing+assembly,10147

[/URL]

Thanks for the detailed reply. I'm looking at parts on RockAuto and it looks like I can get a whole sending unit for about $50, but they also sell just the pump with what looks like several O-rings. Do you have any advice on whether I'd be better off buy a whole assembly from one of the cheaper brands versus spending the same amount for just the pump from a more name brand manufacturer? I am not familiar with many of these brands listed here.

These are the available full sending unit assemblies: (quite a lot of price variance)

And these are the available pump only kits:

Any advice appreciated. Thanks,

 

[J_C]

I don't have a simple answer. The pump itself is most likely but the older these vehicles get, the more that it could be the other parts. I'd hook up a meter to try to see if I could get an AC frequency on the pump power rail to figure out if it has the right RPM. If it does not, then the pump is "probably" the primary problem, unless the sock or filter is clogged. I'm not even sure I could get a reading that would tell me if the RPM is good, but that's something free to try.

If the pump does have the right RPM, then I'd want the pressure regulator replaced which looks like it's part of the sending assembly. It could instead be that your pressure regulator is fine, pump too, but it's the hose on it that split. If you're really aiming for cheapest repair possible then you might want to take it apart first to see if you observe that. If the regulator has cracked apart and leaks, you might see that instead. It's near 22 years old, the whole thing is due for replacement.

The thing is I wouldn't want to choose. I would not get a cheap sending unit assembly with a cheap pump in it, unless you just need to get it running to sell it soon, as the pump may have a short lifespan. I'd get the Delphi HP10135 sending unit w/pump, or if you are forced to spend less, then get a quality pump so at least that should last a while, but then you may find you need a new sending assembly anyway (which are also sold separately), and to take the tank down again to do that.

So, if I only had ~$75 and had to get it from Rock Auto, I'd get a Denso pump w/strainer or strainer separately, then hate myself for not getting the sending unit if it turns out that the pressure regulator was the problem, but Rock Auto has their pumps priced about where I see their quality, that the Bosch is the best then Denso, then Delphi, and I wouldn't buy any of them below that, especially not in the economy section. Remember to get a strainer sock if it doesn't come with one.

Keep in mind that eventually the fuel gauge sensor on the sending unit may fail too.

Having written that much, I'd also look elsewhere besides RA. That Delphi is cheaper on Amazon at $138 plus free shipping:

Amazon.com: Delphi HP10135 Fuel Pump and Hanger Assembly with Sending Unit: Automotive

Buy Delphi HP10135 Fuel Pump and Hanger Assembly with Sending Unit: Electric Fuel Pumps - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

You can probably get a Bosch pump on ebay for around $70 with the hose. That might be the best non-Rock Auto alternative for the pump alone, alone meaning with strainer and hose but not sending assembly.. Here's one for $56, but considering the seller I've no idea if that's a good or old stock source:

Fuel Pump and Strainer Set-(New) Bosch 66085 | eBay

Find many great new & used options and get the best deals for Fuel Pump and Strainer Set-(New) Bosch 66085 at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[adgalloway]

I don't have a simple answer. The pump itself is most likely but the older these vehicles get, the more that it could be the other parts. I'd hook up a meter to try to see if I could get an AC frequency on the pump power rail to figure out if it has the right RPM. If it does not, then the pump is "probably" the primary problem, unless the sock or filter is clogged. I'm not even sure I could get a reading that would tell me if the RPM is good, but that's something free to try.

If the pump does have the right RPM, then I'd want the pressure regulator replaced which looks like it's part of the sending assembly. It could instead be that your pressure regulator is fine, pump too, but it's the hose on it that split. If you're really aiming for cheapest repair possible then you might want to take it apart first to see if you observe that. If the regulator has cracked apart and leaks, you might see that instead. It's near 22 years old, the whole thing is due for replacement.

The thing is I wouldn't want to choose. I would not get a cheap sending unit assembly with a cheap pump in it, unless you just need to get it running to sell it soon, as the pump may have a short lifespan. I'd get the Delphi HP10135 sending unit w/pump, or if you are forced to spend less, then get a quality pump so at least that should last a while, but then you may find you need a new sending assembly anyway (which are also sold separately), and to take the tank down again to do that.

So, if I only had ~$75 and had to get it from Rock Auto, I'd get a Denso pump w/strainer or strainer separately, then hate myself for not getting the sending unit if it turns out that the pressure regulator was the problem, but Rock Auto has their pumps priced about where I see their quality, that the Bosch is the best then Denso, then Delphi, and I wouldn't buy any of them below that, especially not in the economy section. Remember to get a strainer sock if it doesn't come with one.

Keep in mind that eventually the fuel gauge sensor on the sending unit may fail too.

Having written that much, I'd also look elsewhere besides RA. That Delphi is cheaper on Amazon at $138 plus free shipping:

http://[URL]https://www.amazon.com/Delphi-HP10135-Hanger-Assembly-Sending/dp/B0077G6DTW

[/URL]

You can probably get a Bosch pump on ebay for around $70 with the hose. That might be the best non-Rock Auto alternative for the pump alone, alone meaning with strainer and hose but not sending assembly.. Here's one for $56, but considering the seller I've no idea if that's a good or old stock source:

http://[URL]https://www.ebay.com/itm/Fuel-Pump-and-Strainer-Set-New-Bosch-66085/362814362599

[/URL]

Thank you, you've been super helpful. I'll post back after I'm done to let you all know how it went.

 

[masospaghetti]

In addition to J_C's comments, stick with a high quality pump. In my opinion Denso is always top notch. Bosch and Delphi would also be fine. I used a Bosch pump kit recently to replace my fuel pump without any problems.

I'd stick with Amazon or Rockauto personally, I have gotten counterfeit merchandise from eBay before...

 

[adgalloway]

In addition to J_C's comments, stick with a high quality pump. In my opinion Denso is always top notch. Bosch and Delphi would also be fine. I used a Bosch pump kit recently to replace my fuel pump without any problems.

I'd stick with Amazon or Rockauto personally, I have gotten counterfeit merchandise from eBay before...

Finished it up today, problem solved! Thanks for all the good advice.