92 Explorer floods and backfires

Checking fel pressure the way you are is, sadly, a fools errand. The results can be misleading, erroneous or lead you in the wrong direction....

I've seen too many DIYers led astray (and even been led astray myself) with an inadequate fuel pressure test.... The best plan, when ruliong our fuel delivery concerns, it to verify the fuel pressure with a gauge.

FWIW... you're going to have a real hard time taping sheetrock with a 4 inch trowel..... a burger ain't a burger without a barbecue... and you can't check fuel pressure without a gauge....

Thanks Jim. I realize I am not following proper procedures, and my guesses are just that, guesses.

I've seen your name on many posts here, so I'm assuming you know your stuff. On that basis, could you explain how I'm getting fuel in the base. Lets assume fuel pressure is low. Would it be that the injectors cant atomize the fuel with a low pressure, therefore, we get a dribble from the injectors? This dribble then wouldnt mix adequately with air ensuring complete combustion. This unburned dribble then seeps past the rings and winds up in the oilpan?

I guess what I'm asking is : Will the injector atomize (or somewhat atomize) fuel with low pressure?

One more question if you dont mind. Can the fuel pump lose performance over time, gradually losing performance? Or is it an "either its working or it isn't" kind of deal?

Thank you much for the response Justin

Fuel injectors are designed (rather, physics has made them design fuel injectors) to work at a specific pressure drop across the injector nozzle... This is designed to give the optimum spray pattern for the fuel pressure, nozzle shape, orofice size and probably many things my non-engineering background is overlooking. Wander too far from this pressure and it can affect the spray pattern and/or atomization of the fuel. (Both of these are critical for proper combustion and cylinder dispersion of the fuel.

This is why fuel pressure is regulated to the fuel rail.... to be able to "see" this part better... a short lecture on "pressure" and "vacuum".

A "perfect" vacuum is something like 30 inches of mercury at sea level.... to the automotive PCM, this would be zero PSI of MAP (Manifold Absolute Pressure). Zero inches of vacuum (again, we'll stay at sea level), or ambient air pressure would give a MAP reading of about 14.7 PSI. Remember this difference and read on...

And we need to touch on the fuel pressure 'spec' as well.... This is written with the engineers "assuming" that the reader has some previous knowledge. Let's say the spec is 35 to 45PSI - what is meant is 35 PSI at no engine load and 45WITH engine load....

At idle, we expect our car to have 17ish inches of intake manifold vacuum (might be closer to 20 at sea level, but I live and work at about 2000 feet above that and I'm used to 15~17 because of that). At this point, we'd expect to see a MAP reading of 6 or 7 PSI. Knowing that our 'spec' for this example is 35 PSI at idle, we can do a bit of quick math... The pressure on one side of the injector nozzle is 35 PSI.... the pressure on the other side is about 6.5 PSI.... the pressure drop across the injector nozzle is going to be about 29 PSI.

Let's get driving down the road... and let's get into the pedal a bit... First thing we notice is that intake manifold has fallen to near zero inches (meaning our MAP has RISEN to near 14.7 PSI)... and we see fuel pressure has risen to 45ish PSI.. Some quick math and we see that the pressure drop across the injector nozzleis in the neighbourhood of 30 PSI... Probably more than you wanted, but interesting stuff all the same...

While most fuel pump failures manifest themselves with "don't work period" as the first symptom we see.... our driving styles and conditions can and will hide signs of a failing pump from us. Corroded wiring connections, corroded wiring, internal problems with the pump motor or mechanism, restrictions in the fuel lines.... any of these can reduce or restrict the fuel volume and pressure available at the fuel rail. Corroded wiring or connections will affect the wires ability to flow enough current for the pump motor to produce enough torque to build fuel pressure.

For a no start concern... we would check fuel pressure WHILE CRANKING THE MOTOR. For a driving concern, we would check fuel pressure on the road WHILE THE CONCERN IS HAPPENING.

The two main things driving DIY auto repairs - the owner doesn't currently have the finances to have the car taken to a shop or the owner feels pride in being able to say "I fixed that!". (Or, sometimes, both). Either way, I've seen a lot of money wasted on parts that weren't needed... enough money to purchase some of the tools that would have helped in diagnosing the concern (and even might have left some cash in the pocket)... tools that might pay for themselves more than once.

HTH.

Another reason for fixing it yourself is the satisfaction (and secure feeling) of knowing it was done correctly. For example, I recently replaced a selector seal on the auto trans of my '91. I KNOW that the filter was replaced, I KNOW that the correct type and amount of fluid was put in it, I KNOW it got a new pan gasket, I KNOW the seal was installed in the correct direction, I KNOW it was properly lubricated before installation, I KNOW the pan bolts were properly torqued and that none were stripped. If I take to a shop I have no idea what they did. Unfortunately I've had too many occurances where a so-called professional mechanic made a mess out of things. I'm sure there are some good ones out there but they are not very easy to find. I am not in any way pretending to be any kind of high-level auto mechanic but there is a lot of information available to assist us DIYers so we are less likely to overlook something that might be common knowledge to a professional.

First of all, Jim, thanks for the very detailed reply. I do appreciate it. Perhaps I should have mentioned I have an Auto Tech background. Though it seems I have lost much of the knowledge as its a field I never pursued. This will soon become apparent....

I have it figured out now. I know I stated in the original ppost spark was ok. Hah! It was, but only as far as the wires. Never bothered to check the plugs. Put six brand-spankin-new plugs in and the damn thing didnt turn halfways around and it was running. Loudly, but running nonetheless. Apparently one of the backfires blew the muffler apart....... To be lenient on myself, there were other issues with the old girl that led me astray.

The negative battery cable (probably original) had corroded inside the terminal. This led me to believe I had starter troubles. After removing and rebuilding two times (parts come from the local dump and for the record the armature and motor housing from Tempo/Topaz work wonderfully, just use your old planetaries and head piece) I started to think it was not the starter. Cut the cable off and removed all the green crap and it turned like a champ.

Once I got it turning over again, still suspecting fuel, I gave it a couple shots of ether while cranking. It didnt mak an attempt at starting. Hmm, says I, if I had good spark this thing should have caught and ran for a second. Took out the number one plug, grounded it against the alternator bracket and cranked it. Tiny spark, but it was way down in the center electrode deep in the plug. Tried another. Completely dead. Checked the other on the same side. Dead. No need to check the other side of the engine. You can tell I'm no genius lol but even I know a V6 wont run on 3 cylinders. So I guess my methods dont work very well, but all's well that ends well.

Anyhow, its easy to make one bad assumption and be led way off track. I assumed spark was ok, which led me to the fuel delivery system. Which I guess wasn't a REALLY dumb mistake since it all started after replacing fuel filter.

I guess I forgot the KISS method. And my thumb is not an accurate fuel pressure guage, a screwdriver in a plug wire cant tell you if your plugs are good and a starter wont turn well with no path to ground. If you leave a dog on a bone long enough though, he'll get the marrow.

Anyway thanks Jim. Your insight was well thought out, straight to the point and informative. Justin

PS this is just an old clunker that only gets used around the yard.

Well, these old Exploders DO need to be maintained ;-)

And yes, once you figure it out it's usually something simple. If you want to find some really complicated ways to try and find a solution you could try the

Once you eliminate stuff like bad battery cables, spark plugs, plug wires, clogged radiators etc some of the most common problems on these engines are:

leaking intake manifold gaskets leaking head gaskets bad thermostat

I've also read about bad O2 sensors but have not had that problem (yet) personally on my three Explorers.