99 b4000 - random, intermittent total power loss

[LacquerHead]

Howdy all, just had this issue appear on my 1999 b4000 4x4 manual trans with 140k miles. About 150 miles into a trip at highway speeds, the truck seemed to lose all engine power for about 2-3 seconds, then it would magically (as is someone flipped a switch) all come back. All my lights and gauges would still operate fine, just had absolutely NO engine power, and would begin engine breaking. Would do this every 15 seconds or so, so I pulled off the interstate to check my vitals. Everything looked good, so I let it sit for a few minutes and started her back up. Ran fine for a few miles then started doing it again, all the way home. Sitting at idle, it seemed to drop down below 500rpm for a few seconds and then come back up, and occasionally would stall completely, requiring a restart.

This morning, I decided to take it for a drive, and it seemed fine. I am assuming the issue will only show itself after the truck is warmed up. Seems like it must be either a fuel or spark issue. I don't want to start throwing parts at it, but not sure where to start troubleshooting. I am getting no engine codes at all. Seems like more than just a misfire, as I lose all engine power (not just some cylinders) momentarily.

I have compiled a list of things to check and am looking for any feedback or advice: Fuel filter, fuel pump, fuel pump relay, coil pack, and possibly computer. If I could determine whether it is a fuel or spark issue, that would help greatly. I am not thinking its the fuel pump because it ran great this morning even at 60+ mph. Not sure how to go about troubleshooting this as the problem is intermittent, and truck always seems to restart fine. I have a good amount of DIY ability but limited funds, so am trying to guess right the first time.

I greatly appreciate any and all advice and am hoping the issue is something stupid and easy. Thanks everybody.

 

[RonD]

Welcome to TRS

Yes fuel filter, cheap and needs to be changed every 5 years or so


In the cab, passenger side under glove box or behind kick panel you will find the inertia switch, this switch cuts power to Fuel pump in the event of a sudden stop or rollover, i.e. accident
Point of finding this switch is to hook up a test light to it, Ground the test light and then hook up other side to either terminal on inertia switch
While engine is running this light should be ON, if it goes off then power is being cut by Fuel Pump Relay or Computer is cutting Ground to fuel pump relay

You should get a Check engine light(CEL) if fuel pump relay is the problem, but not if its the computer.


Electric motors, like the fuel pump, can become intermittent, it isn't common but not unheard of either, there would be no CEL if pump motor is at fault

If spark was being turned off you should also get a CEL

 

[Spott]

Such an abrupt transition between running and not-running sounds like a spark issue, and certainly not a fuel issue (although it's still a good idea to change your fuel filter).

I'm sure you know what running out of gas feels like, with a gradual loss of power and then sputtering and finally a full stall. If you had a fuel system failure, whether it was a pump shutting off or a blocked line or whatever, your engine would exhibit the same symptoms. Therefore, these are not the symptoms of a fuel system failure. It must be spark.

In my '88 2.9, the PO had replaced the coil with some cheap aftermarket unit that lacked the retaining clips to engage the distributor cable. The connector gradually worked its way loose, and the resultant behavior of my engine was much like yours. It would run just fine when it would run, but it would abruptly stop firing intermittently, and resume running just as abruptly. "Like flipping a switch." It was clearly related to vibration and bumps in the road. That weekend I got under the hood and the problem was quickly identified.

Obviously, the 4.0 doesn't have an actual coil or a distributor, but the same abruptness points rather decidedly towards the ignition system. I'd start by inspecting cables and connectors in the ignition system, making sure everything is clean and tight and not shorting to anything else. Also, pull the codes from the computer and see if there are any hints there.

 

[chewy012]

My vote is the fuel pump relay. Sounds odd, but this sounds like a similar problem I had that was cured by fuel pump relay. I changed everything I could think of, last thing I changed was the relay, haven't had the problem since.

Sent from my XT1254 using Tapatalk