I haven't posted in a while, but I have been trying to troubleshoot an issue with my truck that has been causing it to run poorly intermittently. I purchased new O2 sensors and a new crankshaft position sensor, but couldn't get my old O2 sensors out and haven't had time to mess with the CPS, so I've just been dealing with it for a while. Some days, the truck will drive great...other days, it seems like I'm driving a 6,000 pound 4-banger.

Well, today when leaving work to head home, the truck suddenly lost all power from the engine while accelerating slowly from a stop light. As the truck shifted into 2nd gear (I think..might have been 3rd), suddenly the transmission either started slipping or shifted into neutral on its own, so I quickly let off the gas and coasted a bit, thinking my transmission had just bit the dust. Soon thereafter, the engine completely died, so I pulled over on the side of the road. I had no idea what had just happened, but I popped the hood to look things over. Everything looked normal (no smoke, no dripping fluids, no shredded belts), so I hopped back in the cab and cranked the engine, and after sputtering a bit, it started up and idled normally. I used my OBDII reader to check for pending or logged codes, but none were present.

I let it idle for 20-30 seconds and it seemed to be running OK, and the transmission shifted into drive and reverse and the vehicle moved with no slippage. So, I decided I was going to try to limp to the nearest mechanic that I trust, which was less than 2 miles away. Well, I made it about 1/4 mile when the same exact thing happened again, only this time, the truck was dead for good. I could not get it to even think about starting again. The starter turns over fine and the engine seems to crank freely...but it won't run. Again, there were no pending or logged codes. So, I called a tow truck and had it taken to the mechanic. In hindsight, I wish I would have had it towed home in case it turns out to be something I can handle like a fuel pump or CPS...but whatever, what's done is done.

So, I'm hoping this really is something simple like a bad fuel pump. That may actually explain the intermittent performance issues I've been experiencing. I just thought this past weekend that I should really do a fuel pressure test, but ran out of time and never got to it.

Would loss of fuel pressure cause the transmission to drop into neutral like that? Or could this be something else relatively simple like a bad CPS?

I'm hoping it's not something major like a bad computer, or some bizarre electrical gremlin that will take dozens of hours of troubleshooting, as I probably can't justify sinking a ton of money into this truck since I have a perfectly good 2008 Ram with low miles on it sitting in my driveway. I just don't want to have to put this 2nd gen out to pasture yet, so hopefully this turns out to be something fairly minor.

I'll probably hear something from the mechanic tomorrow and will report back, but I welcome any feedback as I sit here and ponder the worst case scenario....

Thanks in advance.

 

Could be any number of things. The PCM takes its cues from the engine... so, if the engine is being funky, everything else will be as well. At this point, you are going to have to wait and see what the mechanic finds....... could be something simple, at which point, you can just have it towed home, and fix it yourself, just pay for the diags, and the additional tow..... (still and all, might be cheaper just to let him fix it....)

From the symptoms, could be as easy as a bad O2 sensor, all the way to a failing PCM. Wait and see what the mech says, take it from there.

 

As always, I REALLY appreciate your advice. I may run by on my way to work tomorrow and do a quick fuel pressure test and swap in an old (but working) coil just for the heck of it. I can handle a fuel pump replacement if that's all that is going on. But, if it's not an obvious issue, I'm probably in over my head. Plus, like you said, at this point it may be cheaper to just let the mechanic make the repair since the truck is already at his shop.

Can you tell me what the fuel pressure should be with ignition on/engine off, and with the engine running (in case it actually comes to life)?

I'll report back with a diagnosis in case anyone else ever has these symptoms.

Thanks again!

 

Fuel pressure should be around 50 psi. If the problem doesn't show itself when the mechanic looks at you may have to try replacing a few things. Cam crank and ignition coils have been known for intermittent issues that don't trigger a fault code.

 

I'm with you....I'm suspicious of a bad coil. If the shop doesn't get to it today, I'm going to ride by after work and do some quick diagnosis. Before I left my house this morning, I grabbed my fuel pressure gauge and an old coil that was working when I replaced it. I'll see if either of those may be the cause. If it's a bad fuel pump, I may try to replace it right there in the lot over the weekend...the shop isn't open Sat/Sun, so I might be able to get away with it. Haha...we'll see.

Can you test a ignition coil's function with a multimeter?

Thanks again for the input. I'll be sure to post the findings.

 

...but I just swapped in an old coil that had been working when it was removed, and the engine still won't start. I just purchased a new coil from the dealer in case the old coil I swapped in brought it to life, but since that didn't work, I don't want to put in the new coil just to find out that the truck still won't run and then not be able to return the $70 new coil. The shop says their next step is to install a new coil. I have a bad feeling that their approach is to start throwing parts at this rather than doing some real diagnosis. So if I let them do it, I'm out $70 for the coil and $50 for labor....for 5 minutes' worth of work.

So now I'm torn about what to do. Any advice?

 

...and aside from being mad at myself for having the truck towed to a shop instead of my house, I'm really thinking this is either a bad crankshaft position sensor, or a bad PCM (hopefully the former).

I really doubt this is a coil issue since my secondhand coil didn't do anything. The fact that the shop insists on replacing the coil, when I'd bet money they didn't check to see if there is voltage at the coil, really irritates me. In fact, when they called with the initial diagnosis, I told them them I had a spare coil that they could try briefly to see if it solved the problem before I paid them for a brand new one. They said, "well our research says that used or aftermarket coils could damage the PCM." So I asked if they were going to install an OEM brand coil, to which the guy said, "Oh, no we would put in the Carquest brand." So I told him to call the dealer and get a price quote on the OEM coil and get back to me. Meanwhile, I drove to the dealer on my lunch break and purchased a coil, just in case we ended up needing it.

Anyway, I'm going to go do some troubleshooting tomorrow. The shop wasn't really happy that I had swapped coils in their parking lot, but whatever. I'm not getting my money's worth for the $109 I've paid for diagnostic work so far, since I'm pretty sure the diagnostic consisted of checking an online repair database and deciding that a bad coil sounds like the most likely culprit based on repair notes from other trucks, as opposed to simply checking a few simple things on MY TRUCK.

So, my plan of attack is:

1) Check for voltage at coil; if no voltage at coil, check ASD. If ASD relay is good, then start suspecting a bad crankshaft position sensor or bad PCM?
2) If voltage is present at the coil, then check for spark on distributor side of coil; if no spark then check resistance of coil
3) If existing coil checks out bad, then install new OEM coil
4) If coil is good and there is good spark but engine still won't start, then check fuel pressure
5) If I find good spark and fuel pressure, I guess it's time to start looking at possible timing chain failure?

I can't think of any other straightforward causes...am I missing something? My fear is some sort of bizarre electrical/wiring issue that even the most seasoned tech would struggle to find. Or, would it be possible for a catastrophic transmission failure to shut down the engine and prevent it from restarting but not throw a code?

Sorry for my rambling. This just helps me organize my own thoughts. Feel free to chime in if I'm headed down the wrong track...

 

with cold truck key it a couple of times only to run , listen for the fuel pump then depress the shredder valve on the fuel rail it should **** out some fuel if the pump has pressurized the line. when mine died the truck stumbled and it was like some through it in neutral then the motor quit not to restart. it can also be check by giving a healthy blast of quick start directly into the throttle body it should at least pop and attempt to start if it is only the fuel pump. if it is the pump it is in the tank ,witch means a a tank drop or bed removal. don't use a airtec or other cheap one you will be doing it over in a year, ask me i know

 

If the shop just wants to throw parts at it, and are handing you lines about aftermarket coils damaging the PCM, tell them to leave it alone, and have it towed home. I suspect even with the tow bill, it will save you money in the end.

I don't think there is any point in testing the coil itself, considering a used-to-be working coil made no difference.

So, lets start with the basics. Are you getting spark from the coil? Do you have good fuel pressure?

 

Yeah, I totally agree with you. I am going to try to get away with working on it some in their parking lot tomorrow. If I find that there is no voltage at the coil, I'm going to talk to the service manager Monday and tell him I don't think I should pay for the diagnostic fee since all his tech did was essentially browse the internet and then suggest I replace a part without testing to see if that part had power to it. The truck was never even pushed into a service bay. Really irritating.

While I'm sitting here getting my game plan together, it dawned on me that my wife's cousin had the exact same thing happen to him with his Jeep Grand Cherokee this past Thanksgiving day. I had to help him replace his cam and crank sensors the next day. I just texted him to pick his brain, and he confirmed what i remembered - that his transmission went out first, and then the vehicle lost power and would not restart....identical to my symptoms.

So, I'm almost positive that I'll discover tomorrow that there is no voltage at the coil, and that this is most likely caused by a bad crank sensor. I found this in the service manual tonight:

The ASD relay will be shut–down, meaning the
12–volt power supply to the ASD relay will be de-activated
by the PCM if:
˛ the ignition key is left in the ON position. This
is if the engine has not been running for approximately
1.8 seconds.
˛ there is a crankshaft position sensor signal to
the PCM that is lower than pre-determined values.

If I understand that correctly, then a bad crank sensor that will not communicate with the PCM will cause the PCM to shut off the ASD, meaning there will be no ignition.

Am I on the right track?

Thanks again for your input!