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Odd issue with my 99 explorer




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1998Exp

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All second gens, regardless of motor, are wasted spark. Same with any 3rd/4th gens with the 4.0 SOHC engine. I think the 4.6 was the only one that got coil-on-plug.

No vacuum FPR on the return-less systems (99-01).

One wire per plug is not the best indicator of a waste spark system. Waste spark basically fires two cylinders with one computer pulse (one on the compression stroke and the other on exhaust) and it has to do with how Ford decided to control the coil pack (it's easier, cheaper, and requires less programming to fire two cylinders with one wire). Distributor style EFI systems with one plug per wire are also not waste spark.
 




1998Exp

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"Waste spark" system was a neat idea: half the number of coils and no need for camshaft-driven timing (at least not for ignition). The transition to coil-on-plug killed it, eliminating the failure-prone HV wires.
BTW, "waste spark" is a misnomer. There is no spark in the opposite cylinder, because its plug is practically shorted by the high water content in the exhaust gas.
 




Mbrooks420

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"Waste spark" system was a neat idea: half the number of coils and no need for camshaft-driven timing (at least not for ignition). The transition to coil-on-plug killed it, eliminating the failure-prone HV wires.
BTW, "waste spark" is a misnomer. There is no spark in the opposite cylinder, because its plug is practically shorted by the high water content in the exhaust gas.
If there’s no spark why does the one bank always have much higher wear?
 




jmops

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The real reason for wasted spark is cost reduction after converting from distributor type systems that (usually) had one coil for all cylinders. You only need one coil per 2 plugs and one computer output driver (distributor points & condenser equivalent) per 2 plugs. Any programming difference is trivial and amortized over several million cars. Any 2 cylinder lawn mower engine these days has wasted spark for the same reason.

COP engines ratchet up the coil cost but eliminate the high voltage wire cost and subsequent reliability problems. It's also possible some savings are made in using lower power, cheaper computer driver chips even though more are needed due to a halved duty cycle
 




1998Exp

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If there’s no spark why does the one bank always have much higher wear?
Because the current flows in opposite directions - in one bank from the center electrode to ground; in the other bank it's the other way round. Or, if you will, in one bank the firing voltage is positive and in the opposite it's negative. I am not sure which is which, but it's not too hard to figure out. Material erosion depends on which way the electrons go. That's why OEM plugs were different PN for opposite banks. Aftermarket plugs are usually all the same, and both electrodes platinum coated.
 




outlawz360

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Sorry it’s been awhile guys, a lot has been going on. It was in the garage and they said the fuel pressure etc is all good. They changed the coil pack pig tail as they said that was it but it still has the issue. It’s very mind boggling, just can’t figure it out. No check engine light comes on or anything no codes either. I don’t notice any mpg loss, I don’t know what to even check next or replace :frown:
 




jmops

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When it's in the no-start condition touch only one thing at a time. My first try would be to take off one spark plug wire and attach it to any old plug you have around. Ground the plug body to engine metal and have someone else try to start it while you check that plug for spark. If it does you have basically eliminated everything electrical except timing. So then you make the next guess - I'd check fuel rail pressure.

I suppose it could be something strange in the ECU that has been triggered by some odd sensor fault and it finally reverts to the cold start code. I haven't had my Exp long enough to know what the start/picking-up-the-timing code looks like but it can be done many ways. My 98 Saab just fired all plugs at a high frequency and figured it out on the fly without any cam sensor at all on the engine and my 98 GM v6 could do it OK when the cam sensor had failed, so I presume Ford has some smarts in the ECU as well....that may be activated only when it's doing a cold start.
 




Mbrooks420

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I’d still place some money on a failing fuel pump.
 




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jmops

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My Exp is just the opposite. One out of maybe 3 or 4 times it won't start when cold no matter how long I leave it crank. However, very time it happens I just stop cranking and then do it again and it fires immediately. I'm guessing it's a fuel pump that needs a second nudge or a relay but I'd need to be have a fuel rail gauge already hooked up and visible to catch it.
 




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As soon as it acts up don't keep cranking stop and test the pump
Can Also try to cycle the key a few times before starting

@koda2000 is our fuel pump except he usually nails it
 




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It has new motorcraft plugs and denso plug wires so that’s out And fuel filter, whatever the issue it’s definitely robbing power, the more I push the pedal the worse it gets but it really don’t start till after about 30min of driving or more. I have however noticed it does it if I push the pedal to the floor it stumbles and does it. Definitely No power and it will stall but starts right up again and will go for a few min
 




Mbrooks420

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Fuel pump.......
 








Mbrooks420

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They also claimed they fixed it.
 




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Fuel pump
We see your symptoms a lot on here
 




outlawz360

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They also claimed they fixed it.
definitely got a point there, I found some other testing I can do on the fuel pump, I’ll let you guys know what solves my issue, might be about 2 weeks till I’m able to try and tackle the fuel pump, from what I seen it can be a pain
 




donalds

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Yep gotta check it while it's hot and acting up


I went through this for like a year Is my fuel pump bad 1999 ford explorer shoc 4.0. Lots of pictures on the replacement
definitely got a point there, I found some other testing I can do on the fuel pump, I’ll let you guys know what solves my issue, might be about 2 weeks till I’m able to try and tackle the fuel pump, from what I seen it can be a pain
Here is a link to the whole job Is my fuel pump bad 1999 ford explorer shoc 4.0. Lots of pictures on the replacement
 


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410Fortune

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FUEL PUMP!!!!!!!!!!!!!!!!!!!! I just read this thread, quit dodging around the issue. It is like you will only accept answers that do not include dropping the fuel tank??

57 psi on a cold pump is BELOW SPEC!!!!!!!!!!!!!!!!!! 99 Explorer is returnless fuel spec is 65 psi + or - at 57 you are on the low side. When the pump gets hot it is not going to be able to keep up with demand, This means when the pump is hot it will be even lower
The long starting is because it is not building enough pressure with the first run of the pump


What do you not understand about a minimum of 60 psi operating pressure? The shop that said your pump was okay also said the issue was a wiring pigtail and they were wrong.....
The injectors cannot atomize the fuel properly under 60 psi of rail pressure
Hesitation, bucking, missing, long crank to start and NO CHECK ENGINE LIGHT with 57 psi fuel pressure

YOU HAVE A FUEL PUMP ISSUE, you need a new pump, strainer and fuel filter.
 




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