1998 explorer died, won't start

Hello, I am new to the forum so I hope I'm posting this properly. Anyhow, I've got a dead 1998 explorer which I desperately need to get up and running. Heres the problem. Started having low power problems the truck would lose speed while driving up decent sized hills, started stalling at stop signs and some hesitation while taking off. So I changed the fuel filter after work one night then left to go home, got on expressway and it would not go over 50mph, started slowing more until I pulled off into rest area, pulled into park spot where it died and would not re-start. Tried several times and finally got it to start one more time, but as soon as you put it in gear to try and move it died again. Ended up running the battery down, had a friend come and trailer it back to his garage. The following day I began the troubleshooting process. Replaced fuel pump, charged up the battery- still same results. Thats when I found this site and read about several things to check, including the crank position sensor, which I checked and noticed that it appeared to have been rubbing the toothed gear, so I tried smacking it to see if that would make any difference, and when I tapped it the fuel pump relay started clicking, and another relay or something also clicked and there was a buzzing sound on top of the engine that sounded similar to fuel pump. Anyhow, everytime I barely tap the CKP sensor, it trips the relays, and whatever it is on top of engine. I replaced the CKP sensor and the new one does the same thing, and still it won't start. Has anyone ever heard of this? (thats if my post makes any sense) I'm going back in tommorow morning to try and figure it out. Thanks for your time, sorry for such a long post. cb75

Forgot to mention its a 1998 Ford Explorer 4.0 V6 SOHC 4wd 4dr with around 112,000 miles. And I was able to scan for codes which turned up a "input speed sensor malfuntion" message.

Engine stalled - no restart.

cb75 said:

Hello, I am new to the forum so I hope I'm posting this properly. Anyhow, I've got a dead 1998 explorer which I desperately need to get up and running. Heres the problem. Started having low power problems the truck would lose speed while driving up decent sized hills, started stalling at stop signs and some hesitation while taking off. So I changed the fuel filter after work one night then left to go home, got on expressway and it would not go over 50mph, started slowing more until I pulled off into rest area, pulled into park spot where it died and would not re-start. Tried several times and finally got it to start one more time, but as soon as you put it in gear to try and move it died again. Ended up running the battery down, had a friend come and trailer it back to his garage. The following day I began the troubleshooting process. Replaced fuel pump, charged up the battery- still same results. Thats when I found this site and read about several things to check, including the crank position sensor, which I checked and noticed that it appeared to have been rubbing the toothed gear, so I tried smacking it to see if that would make any difference, and when I tapped it the fuel pump relay started clicking, and another relay or something also clicked and there was a buzzing sound on top of the engine that sounded similar to fuel pump. Anyhow, everytime I barely tap the CKP sensor, it trips the relays, and whatever it is on top of engine. I replaced the CKP sensor and the new one does the same thing, and still it won't start. Has anyone ever heard of this? (thats if my post makes any sense) I'm going back in tommorow morning to try and figure it out. Thanks for your time, sorry for such a long post. cb75

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G'day cb75 - can't say I've got an answer for you - but my '98 XLT did the same thing this morning on the way home from a 12 hour night shift to add insult to injury.

Was way down on power, had to kick it hard to get it up to speed - then when I came off the power to go through a round-a-bout the engine stalled and would not restart......so I had it towed and I'll make some calls next week.

A little history - about 3 weeks back it started running rough - at 60km/h (35mph) it felt like it was "surging" and the engine rpm didn't seem to drop back to idle when coming to a stop - it would hang around 1200-1500 then drop back to idle a second or so after I came to a full stop.

Took it to a local mechanic - had it for a few days - suggested that it may be an inlet manifold problem and suggested I take it to the local ford dealer. Took it to the Ford dealership - had it 2 days (I also requested that they carry out the 160000km service whilst they had it in the shop) best they could come up with was replace the PVC valve.

Marginally better, but still down in power and 10 days later my Explorer stalls and will not restart.

Carried out some roadside troubleshooting whilst waiting for the tow - all fueses good, removed and reseated relays in power distribution block, fuel pump pumping and plenty of pressure at the bleed - about the only test I couldn't do was to check spark.

I'm really annoyed when the mechanics can't diagnose the problem - best they could suggest was a trip to another Dealer 80 miles away!

Hopefully someone will recognise this problem and throw some light on it for us?

Cheers from Oz!

P0320?

cb75 said:

Forgot to mention its a 1998 Ford Explorer 4.0 V6 SOHC 4wd 4dr with around 112,000 miles. And I was able to scan for codes which turned up a "input speed sensor malfuntion" message.

Click to expand...

Was the code P0320? If not, what was it?

P0320 Ignition/Distributor Engine Speed Input Circuit Malfunction

The following is from the 1998 Ford OBD System Operation Summary:

"The ignition system is checked by monitoring three ignition signals during normal vehicle operation:
Profile Ignition Pickup (CKP, commonly known as PIP), the timing reference signal derived from the
crankshaft 36-tooth wheel and processed by the EDIS chip. PIP is a 50% duty cycle, square wave signal
that has a rising edge at 10 deg BTDC.
Camshaft IDentification (CMP, commonly known at CID), a signal derived from the camshaft to identify the
#1 cylinder
Ignition Diagnostic Monitor (IDM), a signal that indicates that the primary side of the coil has fired. This
signal is received as a digital pulse width signal from the EDIS chip. The EDIS chip determines if the
current flow to the ignition coil reaches the required current (typically 5.5 Amps for COP, 3.0 to 4.0 Amps
for DIS) within a specified time period (typically > 200 microseconds for both COP and DIS). The EDIS
chip also outputs status information when the engine is not running.
First, the relationship between successive PIP events is evaluated to determine whether the PIP signal is rational.
Too large a change in 3 successive PIP indicates a missing or noisy PIP signal (P0320). Next, the CMP edge
count is compared to the PIP edge count. If the proper ratio of CMP events to PIP events is not being maintained
(for example, 1 CMP edge for every 8 PIP edges for an 8-cylinder engine), it indicates a missing or noisy CMP
signal (P0340). Finally, the relationship between IDM edges and PIP edges is evaluated. If there is not an IDM
edge (coil firing) for every PIP edge (commanded spark event), the PCM will look for a pattern of failed IDM events
to determine which ignition coil has failed. If the ignition coil cannot be identified or if the engine is running and
there are no IDM edges, the IDM circuit is malfunctioning (P1351)."

Other members have had a lot of difficulty identifying a faulty CKP or CMP sensor strictly from symptoms. Your symptoms are similar to those for a bad CKP sensor. However, you have already replaced the sensor. Assuming that P0320 is the code that you had, I suggest that you check the connection to the CMP sensor. On the SOHC the sensor is located on the driver side valve cover about a fourth of the length aft from the front.

Not sure what the code number was, I'll have to check with the guy who scanned it.

I checked the connection to the CMP sensor and it was OK, removed the sensor from valve cover and the tip was covered with engine sludge. Cleaned off and re-installed sensor then I decided to check for voltage @ connector as described in my manual (Haynes manual says there should be 1.5 volts) Well, There was no voltage going to CMP ?? Also, could the IAC valve be causing my no start problem? With key on you can lightly tap the CKP and it activates the IAC for a couple seconds. I removed IAC from intake and observed the plunger as I tapped CKP and it appears to be stuck.

don't measure to ground

According to my 2000 wiring diagram all of the sensor returns are tied to a common point that returns to the PCM but not to ground. The Haynes' manual should tell you to read the voltage between the two wires at the connector.

When the ignition key is first turned to On, the PCM activates the fuel pump for a few seconds. According to Haynes during cranking the PCM grounds the fuel pump relay as long as the camshaft position sensor (CMP) sends its position signal.

If your IAC valve is faulty, it could prevent your engine from starting if you have never adjusted your idle from stock. Try placing a 1/8 inch thick spacer between the throttle closed stop and the adjusting screw to open the throttle plate slightly. Reinstall your IAC valve and try to start the engine. However, a bad IAC valve does not explain your loss of power.

the 4.0 is known to have problems with the IAC going bad. In most cases you can spray some carb cleaner in it and work the plunger back and forth to break free the carbon and free up the plunger. But like street rod said that doesnt explain your problem with losing power above 1500 rpm.

New CKP wear tabs?

You said that you replaced the CKP sensor. Did the new one come with wear tabs? If so, did you position the sensor so the wear tabs were in contact with the damper to obtain the proper spacing? Did you check for voltage between the two wires to the CKP sensor? It should be about the same as the voltage to the CMP sensor.

Check the TPS output

After thinking about your symptoms more and ignoring your reported DTCs I suggest that you test the TPS output. The PCM relies on the TPS to determine closed throttle for idle and all other throttle positions for acceleration or deceleration. Testing the TPS is easy and costs nothing. With the electrical connector connected to the TPS backprobe the wiper contact (gray/white wire) and the return (gray/red wire). Connect the positive lead of the voltmeter to the wiper probe and the negative lead to the return. Switch the ignition On but do not start the engine. The voltage should be approximately 1.0 volts with the throttle closed. Slowly rotate the throttle plate to WOT while watching the voltage reading. It should increase smoothly (with no dropouts or jumps) to at least 4.0 volts at WOT.

The CKP sensor I bought at auto zone has no wear tabs on it, its just a flat surface as apposed to the old one which had a slight curved edge. I also re-checked power at the CMP connector wires and had only 2mV with the key on. I have not yet tested the TPS, had to quit on it for the night. Also tried gapping the throttle plate 1/8" as you mentioned and still no start. If I remove the fuel pump relay and crank several times it will start for a few seconds. Seems like with the relay in (fuel pump running) it is flooding. I'm planning on going back tommorow for more fun, and I'll check TPS first. Thanks so much for taking the time to read my posts, responding and offering help and advice, it is greatly appreciated!!!

CMP connected for reading?

When you read 2 mv was that at the connector when it was disconnected from the CMP or connected to the CMP? Was the voltmeter on AC or DC? To check the voltage to the CMP the meter should be on DC and I believe the CMP should be disconnected. To test the CMP functionality the meter should be on AC. The CMP is a device similar to what was used in the pointless distributors. The CMP generates a voltage pulse which can only be measured with the meter on AC but the CMP requires a DC supply voltage.

The fact that it runs at all even for just a few seconds is encouraging. If the TPS test passes try disconnecting the MAF sensor and try to start the engine. The PCM will read the wrong voltage (none) coming from the MAF sensor and revert to a stored value. A functional engine will start and idle OK without the MAF sensor but will not run decent under load. If it starts and idles then clean the MAF sensor with MAF sensor cleaner.

The CMP 2mV was checked on DC with the sensor unplugged, across the 2 wires. I also checked funtionality of the CMP using AC as the manual suggests. The TPS checked out OK, and engine still will not start with the MAF unplugged. I disconnected the CKP and found 1.5v DC @ one wire using frame as ground. Now, this is whats confusing me- Not knowing how the CKP circuit is wired, I tried checking for continuity between the other wire (opposite of the wire w/ the 1.5v) and frame ground, and when I grounded the meter lead to frame, The fuel pump relay, and IAC valve clicked/ activated. Plugged CKP back in and if I lightly tap it with my finger, Same thing happens????? I don't understand why tapping the CKP makes this happen, Could I have a bad connection in the connector? I know there are 2 wires going to the CKP, one supplies voltage, the other would have to be a signal wire for the AC pulses right? or is it a ground that could be a bad connection causing my problem?

CKP part of ignition system

Ford considers the CKP sensor part of the ignition system. The dark blue wire goes to pin 21 of the PCM. The gray wire goes to pin 22 of the PCM. The black wire grounds the shield around the other two wires. My wiring diagram doesn't show which is the source and which is the return but I suspect the gray wire is the return. I believe a small current is supposed to flow continuously thru the sensor. When the missing tooth on the damper comes around it creates a pulse in the flow. If there is a loose connection then tapping it might look like a pulse to the PCM. The sensor is in a vulnerable location for weather exposure.

I'm concerned about the 2mv reading on your CMP sensor. The dark blue/orange wire goes to PCM pin 85 which my wiring diagram labels as the input. The gray/red wire goes to a common for the output shaft speed sensor, the ECT sensor, the TPS, the DPFE sensor and returns to PCM pin 91 labeled as signal return. Try measuring the voltage between the CMP gray/red wire and the TPS gray/red wire. It should be 0 volts. If it is, then turn the ignition Off and measure the resistance which should be less than a few ohms. I suspect that the gray/red wire path from the CMP sensor to the common point is open. The common is located near the wiring harness take out to fuel injector #6.

I'll try that in the morning. Where could I get a good copy of a wiring diagram? My haynes manual doesn't have a specific diagram for the 98 4.0 SOHC.

wiring diagram

I found a used one for my 2000 on eBay for about $10. The ones is the Haynes Manual are very incomplete.

Ok, I checked voltage between CMP and TPS gray/red wire, it was 0 volts, Checked resistence between same and it was below 1 ohm. Re-checked voltage @ CMP and it was around 28mv, also had 28mv @ TPS, DPFE etc. Traced wire (gray/ red) back to the PCM and backprobed it there and it too was @ 28mv. Now, if I remove the fuel pump relay and crank the engine, it will start, put the relay back in and it will remain running, however it runs bad and very rich. I'm assuming that since I don't have proper voltage @ CMP, it is not running in time the way it should. Do I have a PCM problem causing it to not put out proper juice to the sensors?

Can't be right

The gray/red wire that's connected to the CMP sensor, the TPS, DPFE and the PCM pin 91 is the common sensor return. You said you read 28 mv at the TPS and DPFE. But you also said you tested the TPS and it was OK? What are you connecting the probes to (besides the gray/red wire) for the 28 mv reading? If it's ground then the 28 mv reading is probably OK. You said you only read 2 mv between the gray/red wire and the dark blue/orange wire with the CMP sensor disconnected and the ignition On. Please check that one more time.

In the original post you stated that you could hear a buzzing sound on top of the engine when you tapped the CKP sensor. Now you've found that you can start the engine by removing the fuel pump relay and once started the engine will continue to run if you put the relay back. Have you tested your fuel pressure? I'm beginning to think that your fuel pressure regulator is bad and is overpressurizing the injectors. When you remove the fuel pump relay it disables the fuel pump allowing the pressure to drop. The buzzing sound could be the regulator. It is located under the upper intake manifold, near the firewall, toward the driver side. It has a vacuum line attached to it. If you go to Post #7 of the following link, the third photo shows the engine with the upper intake manifold removed. The fuel pressure regulator is just visible behind the ignition pack.
Starting my 00M12 Installation
Place the end of a piece of hose in that area and listen for the buzzing. Also check the vacuum hose and connection to the fuel pressure regulator. With no vacuum, the regulator allows the maximum pressure in the fuel rails.
It would also be helpful if you borrowed a code reader, read and note the existing codes, clear all of the codes, start the engine and read any new codes.

Im just going to through this in here, i didnt read all of the threads but i just had one at my shop with this problem and it was the idle air vavle, also i had one with this problem and it was a plugged cat. Im not by any means diagnosing your vehicles just giving you some infor to consider.

When checking the gray/ red wire at the various sensors, I backprobed the gray/ red wire and attached the other probe to ground (negative battery post). I should not have listed the TPS as being @ 28mv, It was the Intake air sensor that I checked- my mistake. The buzzing sound turned out to be the IAC valve which I removed and inspected and to me it appears to be stuck. I have not checked the fuel pressure yet but I have located a fuel pressure test kit that I will have access to in the morning, So I guess that will be my next step. Thanks again for your help, and I apologize if my posts are confusing, a lot of this is somewhat new and confusing to me!