97 Explorer Cold start issues and diagnostic

First post here. I try and do as much homework as I can and after scanning the 3600 threads in this forum, I still have some questions. I have limited experience working with vehicles but am willing to try most anything. So forgive my ignorance on some issues and I won't be insulted if you talk down to me and hold my hand through this.

My 97 Exploder, 4.0L SOHC, 148k, has been sitting in the drive all winter because I can't get it started. I knew this was coming as last year, I had issues but was always able to get the thing fired up.

Last year, when I tried to start it, I would turn on the lights and put the key in and to the ON position. I wait for the instrument lights to turn off, turn the lights off, then add some pressure to the gas pedal. I'll engage the starter and it will crank, crank, crank. Sometimes it will spudder a touch. If I let off the starter, there's no hope of getting it going. But if I remain on the starter (I know, I'm frying it) I will get another spudder and it will eventually catch and fire up. Now, I have to keep my foot on the gas a bit and hold the RPMs up or else it will die out. Depending on how cold it is, it would take from 5-60 seconds, then there would be a spike of +500-1000 RPMs and I could let my foot off the gas without it stalling. This year, I'm not even getting an initial spudder.

My mechanic said it is probably the fuel pump and way more money than I have to replace it. I'm on an extremely limited budget to get this running so the more testing I can do before parts swapping, the better. From what I've read, some people had luck replacing the idle air control valve while other swapped some sensors. I'm not sure where to start, so any advise is super welcome.

Thanks for taking the time to help this parasite,
Skora

Welcome to the forum! There's no need to skim the 3600 individual threads, there is a very handy "Search this forum" tool from the Explorer main page. Enter a keyword or two and it will reduce the number of threads you need to skim.

Probably the most productive next step for you would be to get a hold of a fuel pressure gauge. Some of the parts stores offer a "Loan a Tool" program and may have a fuel pressure gauge you can borrow at no cost (as long as you return the tool). You need to find out what the fuel rail pressure is with the key on and engine off (KOEO) and also Key On Engine Running (KOER) if you could get to that point. Also, watch how quickly the fuel pressure drops after turning the key on. I'm not at home so I don't have the fuel pressure specs in front of me, but you could probably find the fuel pressure specs by searching for it.

The need to hold the throttle open sounds like it would either be the IAC or a vacuum leak. The 4.0L, they have had intake manifold gaskets that cause large vacuum leaks.

-Rod

Depending on how far you depress the accelerator, you're actually shutting off the injectors and not getting fuel, as this is intended for flood clearing. :2cents:

As suggested, you need to get a hold of a fuel pressure gauge. Was the check engine light on when the problem started to occur?

Depending on how far you depress the accelerator, you're actually shutting off the injectors and not getting fuel, as this is intended for flood clearing. :2cents:

As suggested, you need to get a hold of a fuel pressure gauge. Was the check engine light on when the problem started to occur?

A few years back, I bought one of those at-home auto repair courses. Waste of money since I didn't have a vehicle to tinker with and I wasn't about to take apart my only working vehicle for education purposes. But, with the class came a few tools, one of which is a fuel/vac tester.

****There's no adapters so I could use some help with how to look for one. How do I look up the type of fitting I need to thread onto the fuel rail (size of the schrader valve?) and what would the other end of the fitting be since its just a hose that it has to plug into?

As for the check engine light, it's always been on. The one time I had it scanned, it listed an exhaust issue. Changed the muffler later and it went off for a week. Then has been on since. I never had it rescanned. :banghead:

It might be easier to borrow a fuel pressure gauge from a chain parts store as they typically come with the Ford adapter. Just don't over tighten the fittings as that will destroy the rubber seals.

-Rod

Rod,

The gauge he's talking about is the old school Vac/fuel for mechincal pumps/carbureted applications and there is no "adapter" for this as it only reads up 15-20 lbs of pressure standardly.

skora,
That said what you need is a EFI fuel pressure gauge (reads in excess of 70lbs). There are different fittings between manufacturers. If you look on your fuel rail (where all the injectors are plugged into above the intake) at one of the ends you will find a scrader valve that the gauge threads on to. A typical EFI system should run from 45-55 lbs of pressure. I'm not sure of the exact spec for you at the time.

Another thought too based on the 'exhaust' issue is a clogged catalytic converter could be the culpret, but check the fuel pressure out first.

Rod,

The gauge he's talking about is the old school Vac/fuel for mechincal pumps/carbureted applications and there is no "adapter" for this as it only reads up 15-20 lbs of pressure standardly.

skora,
That said what you need is a EFI fuel pressure gauge (reads in excess of 70lbs). There are different fittings between manufacturers. If you look on your fuel rail (where all the injectors are plugged into above the intake) at one of the ends you will find a scrader valve that the gauge threads on to. A typical EFI system should run from 45-55 lbs of pressure. I'm not sure of the exact spec for you at the time.

First off, Rod and Wrightz28, thanks a ton for helping me out. I truely do appreciate you taking time to help a complete stranger. And yes, I am stranger than most. :screwy:

Reading you're post before I headed out this afternoon saved me lots of asprain from the headache I would have gotten looking for items that don't exsist or work. The autozone websited didn't list fuel pressure testers as one of the loan a tool programs but I did find el cheapo fuel test kit at Harbor Frieght for $15. Acceptable cost, but I doubt I'll get more than a handful of uses out of it. But this is what I found. At Idle, 32 psi on the fuel line. Haynes says 30-45. The ambiant temp though is in the 50s and when I went out to try it, absolutly no problesm starting up even after having sat for a month since it was last started. I'm guessing the fuel pump is fine. But we are going to have some cold mornings again at the end of next week and I'll try the test again.

While I had my Haynes out, I ran through the test they had for the IAC. The voltage from the PCM in the harness was 11.92v. Spec is 10.5-12.5. Resistance across the terminals of the IAC was 9-10 ohms. Spec is 6-13. But when I went to check the resistance between either of the terminals of the IAC and the housing, I didn't get a blip. Spec is greater than 10k. I tried 2 different meters and neither of them registared anything. Is this significant or did I screw up the test?

Not getting a reading is essentially an open circuit as far as your meter is concerned. That would be greater than 10k ohms, so I don't think you have a problem there or with your method for making the measurement.

Does the Haynes manual give a spec for the fuel pressure at Key On, Engine Off (KOEO)? You should take that reading as well, then turn the key off and make sure the pressure doesn't drop in a matter of a few seconds.

-Rod

Alright, after a spell of cold weather and then some warm weather to do some more testing, I have more info to continue this game. But, not to make anything too easy, I've lost either the battery or starter on the truck also. When it rains it poors. So first, lets get it running in warm weather.

Symptom is a fast clicking when holding over the key. I tried jumping the explorer with my regal (alone so the buick was at idle) and that didn't start it either. So I put the volt meter on the battery and it read 11.5v I think. Tried starting it and it was under 6v with the load. Is this normal or do I take the battery in for testing. It was bought from Costco maybe 3 years ago and really hasn't had a ton of use. The battery terminals are not corroded as they were greased when the battery was installed.

Back to the real issue:
Fuel pressure is good in cold and warm temps. 40+ psi with KOEO. Spec is 30-45. Hold pressure after 5 minutes spec'd at 30-40. That also was upper 30s. Test were done when ambiant was mid 20s and also in the 50s. Same results. Is this enough to validate the fuel pump as functioning properly?

Some other test I've run as recommended in my Haynes was sensor resistances and harness voltages. Here's what I've found with specs in the paranthesis.

Intake Air Control Valve - IAC
Resistance - greater than 10k (10K+)
harness voltage - 5.02v (5.0 +/-.1)

Throttle position - KOEO test
Harness ground + reference 5.02v (5.0 +/-.1)
I don't know how to probe the connection to test the ground and signal voltages with the sensor and harness plugged in. If anyone has a suggestion for that, I'd appreciate it.

Mass Airflow Sensor
Sensor resistance - closed circuit (open circuit means failed sensor)
Harness - KOEO 4.52v (10+volts) see IAT also
Also, I couldn't check the voltage being sent back on the signal line since it is the same issue for the throttle position test.

Intake Air Temp
Sensor resistance - 57 degrees = 54k ohms (this checks out on the chart for that temp) I couldn't take a second reading to see if the resistance went down at a higher temp because this is when I found the engine wouldn't start. To bad I didn't do the test the day before when it did start.
Harness- 4.5v (5.0 +/-.1) I believe this harness and the MAF are bundles together which leads me to believe they share the same power feed.

So to sum up my questions from this post:
1. Battery or Starter or a different test?
2. Is the low voltage on the IAT and MAF harness a resonable explaination of why I have the cold weather problems I do? If so, how do I test the harness and the power source that feeds the harness?

The unfortune part of my available time and the weather is I'm not expecting any more cold snaps that will facilate more testing in the problem conditions or see if an attempted solution is the correct one.

Again, thanks for all the advise,
Skora

Your battery is definately a problem. Anything under 12.2V is generally not enough to power the starter. Further more a voltage drop to less than 9.6 when cranking would indicate either a power hungry starter or weak battery. I would say safe bet it's the battery there.

Oh, on the other issues, your fuel system sounds fine, glad you checked it before just assuming? :lol2: Like I tell everyone, if you want to do your own work now a days, a f/p gauge is a MUST HAVE along with a scanner.

As for the TPS, you must backprobe the wiring. You could buy inductive test leads that pierce a teeny hole in the wire casing to read them. When done, put a small amount of tape over the area pierced to prevent future corrosion from this. OR, you could use your standard leads and CAREFULLY assert them into the connector and tap the pins, but I personally recommend going the first route, much easier.

As to whick 2 wires to probe, I'll let one of the other handle as I'm not overly familiar, however there should 3, ground (normally black), 5V power supply and the reference signal which I'm accustomed to GM which would read around .05 closed and swing to 4.5V at wide open throttle, however it is my undersstanding Ford is the reverse opposite and begins at your listed 5V +/- then reduces to .05V.

As to whick 2 wires to probe, I'll let one of the other handle as I'm not overly familiar, however there should 3, ground (normally black), 5V power supply and the reference signal which I'm accustomed to GM which would read around .05 closed and swing to 4.5V at wide open throttle, however it is my undersstanding Ford is the reverse opposite and begins at your listed 5V +/- then reduces to .05V. I believe the three wire colors will be primarily greeen, orange and black. I think the orange is the Reference wire (+5V) and the black is the signal Ground wire. The Green wire I think is the signal wire. Assuming the above is accurate, if you probe between the green and the black wire, you will see a low voltage with the throttle closed and the key in the Run position. As you smoothly and steadily open the throttle, you should see a linear rising voltage on the meter. If you see any points where the voltage doesn't change with changing throttle, or it jumps up or down, then back to a linear reading, you have a fault in the TPS.

If you happen to measure between the signal wire and the reference voltage, then you will see a steadily decreasing voltage as you open the throttle.

Your readings could increase or decrease, it all depends on what you pick as the meter's ground reference. Fords expect to see a low voltage when the throttle is closed and a high voltage at Wide Open Throttle (WOT).

-Rod

I think just shy of a year, an update is due just to close this out if someone else stumbles across this with the same problem. I'd also like to throw a shout out to Rod and Wright, your help and knowledge has been truly appreciated. If you ever need computer help, look me up on tomshardware.com forums. I'll take care of you! :)

Before I bailed on the explorer, I decided it deserved at least my mechanic looking at it. On a warm (mid 30s) Jan Sun, got it started and left it at the shop. It was warm still on Mon and he pulled it into the garage and gave it a look over. Nothing obvious so outside it went. I promised him it was a 100% reproducible condition and it made me out to be a giant liar :nono:. It started every single morning for a month in a good range of temps for him. The only thing he can attribute the miracle to is they did a wiggle test on all the sensor connections. So one of the sensors I wasn't playing with must have been seated just right that the colder it got, the more it contracted and broke contact. If it was close enough, maybe it would arc enough to get running until it warmed up enough to expand and then run properly.

Lesson learned, when nothing else seems to fit, unplug and replug all the connections, might be something that simple. Hope this can help someone else that has issues and they don't lose months of time on the vehicle.

Thanks again, this forum rocks :cool:

Great, thank you for the follow-up post! Hopefully it continues to give you as much service as you want from it.

-Rod

lol, poltergiest fix. :lol: