Random Stalling/Stumbling

[albi1cnobi1]

Hey guys. My 99 mounty(SOHC V6) recently started having an interesting problem. At random times it will stumble when accelerating, sometimes stalling sometimes picking back up and running normal. When it does stall it will start right back up immediately and run fine. I have not been able to re-create the issue, the truck will idle all day long never stumbling once. It just happens when driving. I've checked the TPS and it seems to check out and I've also cleaned the IAC valve. Not throwing any codes so I thought I would throw it out there and see if anyone had any ideas. Thanks in advance for any help.

 

[BlueHell]

Maybe the fuel filter?

 

[albi1cnobi1]

Fuel filter was replaced about a year ago. I guess it's not out of the question that it may be clogged or fouled by bad fuel.

 

[2000StreetRod]

crankshaft position sensor, fuel pump?

You might try cleaning the crankshaft position sensor connector and checking the fuel pressure.

 

[albi1cnobi1]

You might try cleaning the crankshaft position sensor connector and checking the fuel pressure.

Thanks for the info... is there a way to check the fuel pressure while driving? I'm wondering if the FP is dropping off here and there. Like I said in the OP it will idle all day long. I'm still going to check it though. Anyone know the FP range for a 99 SOHC?

EDIT: Nevermind, I found the fuel pressure range. Thanks.

 

[albi1cnobi1]

O.K. here's an update. I cleaned the CPS connector, it looked fine but cleaned it any way. I checked the fuel pressure. When I turn on the key(without starting) the pressure comes up to about 20 psi. Once the truck starts the pressure comes up to 62 psi. When I run the truck thru the RPM range the pressure only varies about 1-2 psi if at all. Does this sound about right? I'm trying to figure out a way to monitor the pressure while driving to see what it looks like when the issue happens. I'll update with any findings. Anyone have any other ideas on what to check for? I've heard people mention cleaning the EGR valve and checking the DPFE sensor. Sound like a way to go? Thanks again.

 

[2000StreetRod]

cycle the ignition switch

. . . I checked the fuel pressure. When I turn on the key(without starting) the pressure comes up to about 20 psi. Once the truck starts the pressure comes up to 62 psi. When I run the truck thru the RPM range the pressure only varies about 1-2 psi if at all. Does this sound about right?

When you switch on the ignition the fuel pump only runs for a second or two. That's probably why the pressure was only 20 psi. Cycle the ignition switch a couple times. By the third cycle the pressure should have increased to 60 psi. 62 psi is the same as mine when it was stock.

I'm trying to figure out a way to monitor the pressure while driving to see what it looks like when the issue happens. I'll update with any findings. Anyone have any other ideas on what to check for? I've heard people mention cleaning the EGR valve and checking the DPFE sensor. Sound like a way to go? Thanks again.

I suspect that your fuel pump may be going bad but suggest other tests before replacing it. The fuel cools the pump. When the tank is warm and the pump is weak it is more apt to have a problem. The PCM disables the EGR at idle and heavy engine loading. If the EGR valve was sticking open you should notice that when dropping the engine speed to idle. When you tested the TPS did the resistance increase and decrease uniformly with no drop outs: Ford Explorer - Ranger TPS Test Procedure

Have you cleaned the MAF sensor with MAF sensor cleaner?

How old and what type and gap are the spark plugs?

How long since you've added a bottle of fuel injector cleaner to the fuel tank? I use only Techron fuel injector cleaner.

 

[albi1cnobi1]

I suspect that your fuel pump may be going bad but suggest other tests before replacing it. The fuel cools the pump. When the tank is warm and the pump is weak it is more apt to have a problem. The PCM disables the EGR at idle and heavy engine loading. If the EGR valve was sticking open you should notice that when dropping the engine speed to idle. When you tested the TPS did the resistance increase and decrease uniformly with no drop outs: Ford Explorer - Ranger TPS Test Procedure

Yeah, when I tested the TPS it was smooth all the way with no dead spots.

Have you cleaned the MAF sensor with MAF sensor cleaner?

No, I haven't tried that yet. I'll grab some today and give it a shot.

How old and what type and gap are the spark plugs?

Spark plugs are only about a month old. They are stock plugs gapped at .055. Just had a thought. I have a Screamin' Demon coil pack and they recommend gapping the plugs at .065 for the stronger spark. When I changed the plugs and wires I forgot and gapped them at .055. Do you think this could be an issue?

How long since you've added a bottle of fuel injector cleaner to the fuel tank? I use only Techron fuel injector cleaner.

It's been a very long time.

 

[2000StreetRod]

coilpacks

According to my past research:

OEM Coilpack
Spark gap - 0.052 to 0.056 inches (Owner's Guide)
Primary resistance: 0.3 to 1.0 ohms (Haynes Manual)
0.5 ohms measured
Secondary resistance: 6.5 to 11.5 Kohms (Haynes Manual)
13.0 Kohms measured

Davis Unified Ignition/Performance Distributors Screamin Demon 31738
Spark gap - 0.060 to 0.065 inches
Max secondary voltage: 45,000 volts

The Screamin Demon has a higher secondary voltage than the OEM coilpack. This is usually achieved with a different transformer winding ratio. The PCM controls ignition timing by interrupting the flow of current in the primary winding of the transformer (coilpack) causing the electromagnetic field to collapse. I suppose that using the stock gap with a high voltage coil could result in early firing of the plugs reducing power. If that were the case I'm surprised the PCM would not detect that and report misfire associated DTCs. However, it might be best to regap the plugs to the Screamin Demon specification. Does "stock plugs" mean Motorcraft?

 

[albi1cnobi1]

Thanks for that info on the coil packs. Yes they are Motorcraft plugs, not sure of the number off the top of my head but they are the stock replacements.

 

[albi1cnobi1]

O.K., Update:

I rechecked the TPS and again smooth from idle to WOT. 1.03 at idle and 4.65 at WOT. I also cleaned the MAF with MAF cleaner and the IAC valve with TB cleaner while I was at it. I'm heading down to fuel up shortly and will add a bottle of fuel injector cleaner at that time. Tomorrow when I get done work I will pull and re-gap the plugs to .060. I'll drive it for a bit, see how she acts and report back. Thanks for the help 2000streetrod, I'll let you know how it goes.


P.S. I took your advice on the 20 psi thing and tried cycling the key. 1st time 20 psi, 2nd 40 psi and 3rd 60 psi just like you suggested.

 

[albi1cnobi1]

UPDATE :


O.k. so I cleaned the MAF, IAC, and the throttle body. I've checked and set my idle voltage to 1.03vdc, and it just barely idles with the IAC valve disconnected. Before I did this it would just stall as soon as the IAC was unplugged. I dumped a bottle of fuel injector cleaner(techron) in when I refueled and I'm at about 1/4 tank again. I'm hesitant to claim victory yet, but after 3 days and about 150 miles(over 6-8 trips all city driving) the problem has not come back. It would happen pretty much at least once per trip before but has been good since performing all of the above mentioned maintenance. I'm crossing my fingers and hoping for the best. Thanks for all of your help 2000streetrod.

 

[lilredex97]

I thought the fuel pressure should go to about 65 on the first turn of the key?

 

[albi1cnobi1]

As did I. But apparently it just primes the system. The pump only runs for a couple of seconds when you turn the key to avoid dry cranking the engine. The pump circuit is designed to only run when the engine is running. The fuel system primes so that there is enough pressure to start the engine once cranking starts and the pump can take over full time.

 

[2000StreetRod]

fuel pressure specs

My 2000 Explorer/Mountaineer Workshop Manual states that the fuel pressure for the returnless system should be 65 psi +/- 8 psi. It doesn't mention how fast the pressure should build after pump activation nor how long the pressure should remain after pump deactivation. On my vehicle the check valve doesn't leak and the pressure only drops from 62 psi to about 20 psi overnight. Anytime the PCM senses rotation of the crankshaft via the crankshaft position sensor it will energize the fuel pump unless the inertia shut off is activated. I suspect that 20 psi is adequate for the engine to start and idle. My Volvo 850 Turbowagon started with only 0.5 psi fuel pressure but would just barely idle. Since installing a Stealth 340 lph fuel pump in my Sport the fuel pressure rises faster than it did with the stock pump.

 

[albi1cnobi1]

My 2000 Explorer/Mountaineer Workshop Manual states that the fuel pressure for the returnless system should be 65 psi +/- 8 psi. It doesn't mention how fast the pressure should build after pump activation nor how long the pressure should remain after pump deactivation. On my vehicle the check valve doesn't leak and the pressure only drops from 62 psi to about 20 psi overnight. Anytime the PCM senses rotation of the crankshaft via the crankshaft position sensor it will energize the fuel pump unless the inertia shut off is activated. I suspect that 20 psi is adequate for the engine to start and idle. My Volvo 850 Turbowagon started with only 0.5 psi fuel pressure but would just barely idle. Since installing a Stealth 340 lph fuel pump in my Sport the fuel pressure rises faster than it did with the stock pump.

What he said. lol!

Still running great, so far so good. Got my fingers crossed, Thanks 2000 street rod.