Odd issue with my 99 explorer

[itzdiddyo]

Hello all. I registered just to throw this out there.

Last summer, i had a similar "crank but no start" situation with my 96 Explorer (4.0L SOHC V6). Short answer, coolant temp sensor. Not sure about the OP's engine, but on mine there are two temp sensors, one for the dash gauge and one for the ECU. They are relatively easy to access and check, simple resistance check should tell you what you need to know. As I recall my new sensor read about 25 Ohms, old part read something way off of that - and the longer I kept the meter attached the higher the value would climb.

My theory is that the bad sensor was sending gibberish to the ECU, and the ECU was interpreting that gibberish as "cold as hell". I believe I read somewhere on the forums at the time that in the absence of good temp data, the ecu will default to an assumed temp of -41°F causing the fuel trim to adjust to richer than Jeff Bezos. Curiously, this did not throw a code.

I discovered this only after borrowing a defective fuel pressure tester from autozone (or maybe the operator was defective?) leading me down the low fuel pressure path and replacing the fuel filter, fuel pump, fuel pressure sensor, checking countless other sensors, electrical connectors and vacuum lines, hitting things with hammers, mass quantities of beer then hitting things with bigger hammers. Then crying myself to sleep. Trust me, this is the short version of the story.

So don't be like me, check your temp sensor or just replace the damn thing, it's only $30 or so at the zone. Maybe this will fix your troubles, maybe not but I hope it helps someone one out there.

-Cheers

 

[Mbrooks420]

Hello all. I registered just to throw this out there.

Last summer, i had a similar "crank but no start" situation with my 96 Explorer (4.0L SOHC V6). Short answer, coolant temp sensor. Not sure about the OP's engine, but on mine there are two temp sensors, one for the dash gauge and one for the ECU. They are relatively easy to access and check, simple resistance check should tell you what you need to know. As I recall my new sensor read about 25 Ohms, old part read something way off of that - and the longer I kept the meter attached the higher the value would climb.

My theory is that the bad sensor was sending gibberish to the ECU, and the ECU was interpreting that gibberish as "cold as hell". I believe I read somewhere on the forums at the time that in the absence of good temp data, the ecu will default to an assumed temp of -41°F causing the fuel trim to adjust to richer than Jeff Bezos. Curiously, this did not throw a code.

I discovered this only after borrowing a defective fuel pressure tester from autozone (or maybe the operator was defective?) leading me down the low fuel pressure path and replacing the fuel filter, fuel pump, fuel pressure sensor, checking countless other sensors, electrical connectors and vacuum lines, hitting things with hammers, mass quantities of beer then hitting things with bigger hammers. Then crying myself to sleep. Trust me, this is the short version of the story.

So don't be like me, check your temp sensor or just replace the damn thing, it's only $30 or so at the zone. Maybe this will fix your troubles, maybe not but I hope it helps someone one out there.

-Cheers

Almost always the Coolant Temp Sensor failure will only be an issue on a motor that is partially warm. A totally cold start is usually no problem, as well as an immediate restart.

 

[outlawz360]

Hey guys, wanted to let you all know that I got the fuel pump changed, it’s not stalling and such anymore however now I got a new problem. Got codes p0171 and 174, got to keep cranking it to start it and it’s running pretty rough. I tested the maf, tps, egr feedback sensor, checked vacuum lines as many as I could anyway, even replaced 2 that were cracked, I’m about ready to blow it up, any ideas would be appreciated. Also the codes started the day before I changed the pump

 

[fast_dave]

When was the last time the Upper Intake Manifold Rubber Gaskets were swapped out?

 

[outlawz360]

When was the last time the Upper Intake Manifold Rubber Gaskets were swapped out?

I honestly couldn’t say, Probly all original

 

[410Fortune]

po171 and 174 it is running lean on both banks

This means that air is entering the system that has not been accounted for, effecting both banks of the engine
The mas air flow sensor meters all incoming air
The 02 sensors tell the PCM how much air is left in the exhaust
The computer adjusts fuel as needed to use up the air
When the computer has dumped as much fuel as it can and still not account for the un metered air you end up with lean codes.
Un metered air usually comes through leaks in the intake
So check your intake tube from the airbox to the engine for loose clamps, missing hoses, or cracks.
Look around the base of your plastic intakes, see any build up of dirt and grime? This is where the engine is sucking un metered air past the failed intake gaskets

On a 99 explorer with a sohc engine and these codes you NEED INTAKE PLENUM GASKETS/O rings. On the 99 sohc engine there are two sets, upper and lower intake plenum O rings. Somebody familiar with this engine can do the intake gaskets in just a few hours, working clean and slow.
Over the years I have fixed p0171 and 174 about 50 times, all 4.0 engines with plastic upper intakes use rubber O rings to seal the intake to the metal engine. The O rings dry out, crack, shrink and can no longer seal. Ethenol in our fuel does not help.
The fix is to replace all your intake O rings.....
Good time to re seal your fuel injectors, new O rings and seats
Also a good time to do a tune up, new plugs, wires and thermostat. Consider a thermostat housing upgrade as well
Parts are cheap, labor is expensive, so while you are in there consider some extra parts as needed.

 

[koda2000]

As @410Fortune stated, on a '99 SOHC 4.0L it is very common to develop intake manifold air leaks on the upper and lower intake manifolds. The O-ring-style gaskets dry out, become stiff and shrink over time. This is likely the cause of your lean codes. It should also be noted that a clogged fuel filter (Ford recommends replacing your fuel filter every 30,000 miles) you can stretch this to 50K, but if the filter becomes clogged to the point where not enough fuel can pass through it to meet demand, lean codes can get set. If you haven't replaced your fuel filter is a long time, you may want to try that first as it's easier than replacing the intake gaskets, but ultimately the intake gaskets will likely need replacement. The best way to find air leaks is with a smoke test.

 

[fast_dave]

I honestly couldn’t say, Probly all original

@outlawz360

After 21 years, it's time to replace 'em...

$9.90 a set: VICTOR REINZ 111026801 (IMPROVED DESIGN over Stock)

5% Off Rock Auto Discount Code: 13432995153839345
Enter your discount code in the 'How Did You Hear About Us?' box

Rock Auto Link: 1999 FORD EXPLORER 4.0L V6 SOHC Intake Manifold Gasket | RockAuto

 

[outlawz360]

@outlawz360

After 21 years, it's time to replace 'em...

$9.90 a set: VICTOR REINZ 111026801 (IMPROVED DESIGN over Stock)

5% Off Rock Auto Discount Code: 13432995153839345
Enter your discount code in the 'How Did You Hear About Us?' box
View attachment 316713

Rock Auto Link: 1999 FORD EXPLORER 4.0L V6 SOHC Intake Manifold Gasket | RockAuto

View attachment 316714

Thank you!

 

[Mr. Squeaky]

This was meant to be I have a 98 with same issue That started 1 week ago. I do all the work myself and this time it was just too much for me. I have this exact issue to the T. I will replace fuel pump and reply back on this I really hope this fixes it. What pump brands can y'all suggest?

 

[Mr. Alligator]

Try Bosch!!!

Run away from cheap ones!

Good luck.

 

[koda2000]

This was meant to be I have a 98 with same issue That started 1 week ago. I do all the work myself and this time it was just too much for me. I have this exact issue to the T. I will replace fuel pump and reply back on this I really hope this fixes it. What pump brands can y'all suggest?

Why are you talking fuel pump replacement? This thread has been about lean codes. Best way to know if your fuel pump is weak/worn out is by testing the fuel pressure at the rail. A '98 should have around 35-37 PSI at the rail.

I've had excellent results with Bosch replacement pump kits. IDK which pump part number is recommended for a '98 though.

 

[outlawz360]

This was meant to be I have a 98 with same issue That started 1 week ago. I do all the work myself and this time it was just too much for me. I have this exact issue to the T. I will replace fuel pump and reply back on this I really hope this fixes it. What pump brands can y'all suggest?

Do the fuel filter also! And clean the tank the best you can before installing a new pump. I got a car quest complete fuel assembly for $204 so far so good. I think some nasty has made it to my injectors now though Blah

 

[Mr. Squeaky]

Hey guys, wanted to let you all know that I got the fuel pump changed, it’s not stalling and such anymore however now I got a new problem. Got codes p0171 and 174, got to keep cranking it to start it and it’s running pretty rough. I tested the maf, tps, egr feedback sensor, checked vacuum lines as many as I could anyway, even replaced 2 that were cracked, I’m about ready to blow it up, any ideas would be appreciated. Also the codes started the day before I changed the pump

So I read this and I recently watched a video which talked about a Ford throwing both codes and its due to the PCV elbows, because it shows through both codes which are for both banks of the engine.

Found it

 

[donalds]

My vote upper and lower intake gaskets classic

 

[Mbrooks420]

Historically you’re looking at the intake gaskets. Beyond common.

 

[410Fortune]

@koda2000 98 is returnless fuel, should have 65psi (+/-6 psi) at the rail (and one fuel line).

The PVC elbow does not really cause issues on these trucks
The P0171 and 174 codes are 99.5% of the time intake plenum gaskets on your truck

Seriously
This is Explorerforum
We have been building/repairing/fixing these trucks since 1991 around here. I have fixed the 171 and 174 code about 1000000000000000000000 times in the last 15 years, 99.9999999% of the time those codes + 4.0 V6 engine = LEAKY INTAKE O RINGS


AFTER you check fuel rail pressure, AFTER you check the intake tube connections and tubing for any cracks or leaks, THEN inspect the base of the intake plenums and see if there is a build up of soot

I feel like I type this same post every single day..........

ONLY use BOSCH BLUE TOP fuel pump for these 98-01 Explorers ONLY. Dont forget to order a new strainer AND make sure its a real bosch pump not a fake like you can find on Ebay and Amazon. I prefer Rockauto or Summittracing

 

[outlawz360]

Historically you’re looking at the intake gaskets. Beyond common.

The vacuum readings Seem to be where they should be, wouldn’t they be off if the gaskets were bad?

 

[410Fortune]

nope a smoke test, intake vacuum test, these tests do not always find these leaks. A flashlight will though...... or when you remove the plenums you will clearly see where the leaks were.

There is not ONE, not ONE 1999 4.0 V6 engine out there that does NOT NEED new intake gaskets..... they simply just do not last this long, especially with ethenol in our fuel!!!!!!

Listen removing the plastic intakes and replacing the O rings is one of the easiest and cheapest repairs that can be done to these trucks...... It takes me less then 2 hours to complete the whole job and anyone who knows me knows I work like a surgeon, clean clean clean clean is the name of the game....no rush. I can have both intakes off in about 20 minutes working SLOW
Gaskets are like $18

It takes even less time to hookup a fuel rail pressure tester
and it takes only seconds to inspect the intake and plumbing for leaks.....

 

[Mbrooks420]

It’s an easy job. They’re cheap. Just replace them.