engine stalling and sputtering, lack of power

[Beatsmith]

Hi guys, just wanna say that this site has helped me get my explorer back on the road\offroad more then once, so thanks for all the great walkthroughs and posts.

So here's my latest problem, for the last year or so, when the truck is started right after being shut off it kinda runs crappy for a few seconds, a couple taps to the gas pedal has always fixed the problem. But today it decided to stall and sputter after starting it, then it started to run normally, so kinda the same thing its been doing but worse, and this time I have no power on the road, just boggs out anywhere past about half thottle. a few months ago I replaced the MAF sensor and one O2 sensor for an unrelated problem, also theres no check engine light on, wondering if maybe its the other o2 thats going? or a fuel problem maybe... i just changed the air filter last week as well as a oil change.

Oh also when it does its crappy idle after being started when its still hot I generally smell an unburnt fuel smell.

 

[gmbroy]

http://api.viglink.com/api/click?fo...ockauto.com/catalog/more...148&cc=1119631
I sounds like it could be this sensor right here . located to the right of the thermostat housing , on the front of the intake . and you might try a fuel filter . But as roadrunner stated you should do a pressure test

 

[Roadrunner777]

The crappy idle after warm start thing may well be a bad check valve at the fuel pump. Quote from service manual:

"The fuel pump is mounted on the fuel sender assembly inside the fuel tank. This assembly includes a check valve which is in the outlet of the pump. The function of this valve is to maintain pressure in the system after the vehicle is shut down. The pressure retention helps prevent hot start problems."

To elaborate, keeping pressure in the line while shut down helps prevent vaporization of fuel in the line. And, as you might imagine, fuel injectors don't handle bubbly fuel very well. 50 years ago, this was called vapor lock.

To verify this, you can do a leak down test on the fuel rail (just run the engine with a fuel pressure gauge, shut it off and see if it holds pressure). Actually, if you do this, go ahead and write down the pressure values and reply with them.

A less conclusive but cheaper and easier test is to run a bottle of Techron in your next tank. The additive increase the vapor point of the fuel, and if the problem goes away or significantly lessens, then I would go ahead with the fuel pressure test.

With all that said, I think you have had this problem for a while and it is getting worse right now because it's so warm where you live at this moment.

But, I also think you have a second problem, and I'm sorry to say, it sounds like the MAF again.

Are you getting check engine lights at all? If so, if you could read the codes, it would be very helpful. In the meantime, I would inspect the MAF... maybe a bit of moose fur got in there or the connection is loose.

 

[Beatsmith]

thanks for the reply guys, ill see what i find out today and ill let you know, and ill check for moose fur lol

 

[Beatsmith]

so i fired it up this morning, started fine other then a couple extra rotations, and drove fine, full power. so its definately a hot start issue, at least one issue is.
went to crappy tire and found a fuel pressure tester. my truck is a 1993 explorer with the 4.0 v6 auto trans and auto t-case. forgot to mention that earlier.

Ran the fuel pump twice without starting the vehicle - 33 psi
during 10 seconds of idling - 28 psi
after shutting if off - back up to 33 psi and then up to 35 psi
waited 20 mins - still at 35 psi

Ill leave it on for a while longer and see it the pressure drops at all

 

[Beatsmith]

Also there is no engine light on, hasnt been on since i changed the MAF sensor

 

[gmbroy]

Well you might want to check with roadrunner but if it held at 35 for 20 min that should take the check valve out of the equation . From what I have heard & seen here is what I think My ex had the hot start issue I changed the sensor I told you about & cleaned , back flushed , ultra sonic soaked & rebuilt my injectors & the problem went away & has stayed away .

 

[Beatsmith]

ok thats the engine coolant temperature sensor? i have a parts truck so i can just plop that one in and see what happens

 

[Beatsmith]

so I just changed both sensors, the ect and the one right beside it, did some hot starts and it started great, got home and let it sit for about 20-30 mins and started it, and then it idled like poop

i didn't check the thermostat cause the one it the parts truck was done anyways, plus this way i didn't have to drain coolant, just did the ol' switch'a'roo to both sensor, the big one on the right (ECT i assume) looked normal on both vehicles but the other one on the left was really corroded, the parts truck one was not at all so i clean up both connections and put it in.

also i has a pic of the two sensors but i dunno how to post it

 

[natenkiki2004]

If you don't mind another sensor replace, grab an IAT sensor, it screws into the manifold with the same cabling that goes onto the idle air control valve. It helped mine start when cold (faulty sensor thought the engine was always hot).

I also have the warm start issue occasionally (not as bad as it used to be) and have injectors on my to-do list. Not clean them but actually buy professionally rebuilt and upgraded ones.

 

[Roadrunner777]

Ok, 28 psi is low for running pressure. That and raw gas smell point to fuel pressure regulator. There is a vacuum line from the regulator to the vacuum tree... pull that line and check for fuel in it. Then, plug it and do some driving and parking, see if it changes things. The FPR has a diaphragm that can leak and raw fuel gets sucked into the intake manifold through that line.

Glad it's not the check valve, that means you probably are not going after the fuel pump. And, it's normal for pressure to rise after shutdown. If you let it go, it would probably get to the high 30's. Fuel expansion in the lines from heat.

No check engine light though... that's odd. You would think it would throw a too rich code. You may be right about that other O2 sensor.

 

[Gadget X]

I had a similar issue on my 94, turns out that the vacuum hose going to the fuel pressure regulator had "blown off". Something to check that's easy to do! Good luck with it!

 

[Beatsmith]

Ok, changed the IAT sensor, cleaned the MAF sensor, unhooked the battery after for an hour.

Still no luck.

I'll check the vacuum lines tomorrow its getting dark here. thanks for help so far guys, starting to rule stuff out now

 

[Beatsmith]

vacuum lines look bone dry from what i can see, where is the fuel pressure regulator located? i can just swap the one from my parts truck to see what happens.

 

[Beatsmith]

nm i found this post with the info on where it is lol

 

[Beatsmith]

changed the fuel pressure regulator and the throttle position sensor, still doesn't idle quite right after a hot start, seems better though...

 

[vq5speed]

Might try a new TPS $29.00 at Autozone. It fixed my issue of off idle stumbling. Stalling is one of the symptoms of a bad TPS. Oops I see you changed that already. Well maybe fuel filter it helped my problem a little before I did the TPS.

 

[Roadrunner777]

Could you repeat the fuel pressure test, if possible? You should have better numbers now.