Hard start when hot

[ninetyfive]

If I get to temperature and park the car, after 15 minutes it starts right up, but after 30-40 minutes it takes it a good seven seconds of cranking. Starts up right away when cold. Fuel regulator was replaced last year.

Any ideas?

 

[Steve-Indy]

Recurrent leakdown ?

 

[Viper Specialty]

If I get to temperature and park the car, after 15 minutes it starts right up, but after 30-40 minutes it takes it a good seven seconds of cranking. Starts up right away when cold. Fuel regulator was replaced last year.

Any ideas?

Check fuel pressure drop-off and boil-out with a gauge. If it tests OK, what you describe is also a symptom of an impending PCM failure. They start to become erratic when the module gets warm.

If signs point to that, DO NOT TAKE LIGHTLY. G1 modules fail catastrophically in most cases, and the cost different between a partial reman and a total reman + invalid core is thousands different.

 

[DickDavis]

Who does the remans?

 

[Goggles Pizano]

Who does the remans?

He does.

 

[MoparMap]

Check fuel pressure drop-off and boil-out with a gauge. If it tests OK, what you describe is also a symptom of an impending PCM failure. They start to become erratic when the module gets warm.

If signs point to that, DO NOT TAKE LIGHTLY. G1 modules fail catastrophically in most cases, and the cost different between a partial reman and a total reman + invalid core is thousands different.

Is this the same for later gens? My gen 3 has some pretty inconsistent starting characteristics, but I haven't had a chance to get a gauge to hook to the fuel rail yet. Not always a hot start issue either, every once in a while it does it on the first start of the morning, but not nearly as noticeable as after some heat soak. It's not necessarily that it doesn't "start" either, more just like it starts really weakly. By that I mean you hear it catch and fire so you let go of the button and sometimes it just barely keeps itself going at what could only be a few hundred rpm at most before coming up to idle. It's almost like a hit and miss engine where you think it's dead and it just rolls over enough to hit the next cylinder. Giving it some throttle during cranking when it doesn't fire right away seems to pretty reliably start it well though, so thinking it's something else.

 

[Viper Specialty]

Is this the same for later gens? My gen 3 has some pretty inconsistent starting characteristics, but I haven't had a chance to get a gauge to hook to the fuel rail yet. Not always a hot start issue either, every once in a while it does it on the first start of the morning, but not nearly as noticeable as after some heat soak. It's not necessarily that it doesn't "start" either, more just like it starts really weakly. By that I mean you hear it catch and fire so you let go of the button and sometimes it just barely keeps itself going at what could only be a few hundred rpm at most before coming up to idle. It's almost like a hit and miss engine where you think it's dead and it just rolls over enough to hit the next cylinder. Giving it some throttle during cranking when it doesn't fire right away seems to pretty reliably start it well though, so thinking it's something else.

While I have seen it on Gen-2+, its not nearly as prevalent or obvious as with Gen-1 cars. What you describe is far more likely a fuel pressure regulator in the module bleeding off too rapidly and allowing boil-out, and taking time to refill the rails completely.

 

[MoparMap]

While I have seen it on Gen-2+, its not nearly as prevalent or obvious as with Gen-1 cars. What you describe is far more likely a fuel pressure regulator in the module bleeding off too rapidly and allowing boil-out, and taking time to refill the rails completely.

So funny story (or not depending on your point of view), I think a PCM failure is exactly what just happened to me this morning. Went to start it (dead cold start, hasn't run for a few days) and it did its typical "crank a little longer than I was used to", but I let off the button too quick before it could catch itself. Went to try it again and it's completely dead. Zero response from the start button and the whole car is just a bit funny. Pulled the battery cable to try to give everything a hard reset and check voltage just in case it was weak, but battery tested a good 12.4V with my multimeter and cables seemed tight (re-seated them regardless). Got back in the car and I've got nothing. Plugged in my DRB III and the PCM isn't even showing up on a scan, so I think it left the building. Tried to unplug and reseat all the PCM connectors as well and still no life, so I think I'm in the market for a new one or a repair if that's possible.

 

[daveg]

Are you getting voltage to the PDU?

 

[MoparMap]

I'll have to do a little more digging today. Haven't had a lot of time as it was a bit of a morning trying to figure out if I was going to make it to work or not. When the Viper gave up I tried my Dart, but I had just loaded a new tune into it over the weekend and hadn't had a chance to test it yet. Turns out it wasn't very happy with that either, and my wife needed her car for stuff today, so was a lot of running around trying stuff in the moment and less time doing real diagnosis. The gauges don't even do their normal test sweep on key on and the DRB reports no PCM present initially, but if I hit the start button I get a strange report on the DRB of something like "PCM not recognized" instead of just "not connected", but not sure what that means or if it's just coincidence. Will have to check fuses and stuff now as well, though based on the way it's been having trouble starting for a while now, I suspect it's a bigger issue. At least it did it to me in the comfort of my own garage and not in the parking lot at my office.

 

[MoparMap]

Well, that might have just saved me several hundred dollars, though it raises a bigger question as well. ASD fuse was blown, which is PCM power among many other things if I'm reading the diagrams correctly. Looks like it powers some O2 sensors, injectors, and the cooling module as well. So now the question is why did it blow? Replacing a fuse is easy enough, but 9 times out of 10 doesn't fix the real problem. Guess I can try to ohm out all my injectors and other stuff on the circuit and see if anything stands out. I guess it's possible it could have just been weak for a while now, which could have limited injector power and caused my hard starts and it finally just gave up the ghost, but still a bit odd.

 

[GTS Dean]

Is this on your GTS? Let me know if you need a JTEC.

 

[Viper Specialty]

This is G3 correct? Downstream O2 sensor wires in the sill on an aftermarket exhaust, 99% of the time. Dead short on heater supply line.

 

[MoparMap]

Yeah, sorry to hijack original thread. My issue was G3 based. A new fuse appears to have gotten the PCM back online, but wanting to make sure I track down the original cause to make sure it doesn't happen again. I'll have a look at the O2s. I was pretty sure mine were still well covered in the braided loom and not chafing when I put the exhaust in, but easy enough to recheck them all to be sure. Thanks for the tip!

 

[MoparMap]

If I'm reading the manual correctly, the heater circuit has quite the range. It says as low as 100 ohms and as high as 4.5 megaohm. Mine are both testing at 4.5 ohms, so definitely on the low side, but not a dead short. Would kind of explain the fuse going over time vs blowing the second I turn the key on, but still sort of odd to diagnose. I also haven't seen any codes pop up regarding them for what it's worth.

 

[Viper Specialty]

If I'm reading the manual correctly, the heater circuit has quite the range. It says as low as 100 ohms and as high as 4.5 megaohm. Mine are both testing at 4.5 ohms, so definitely on the low side, but not a dead short. Would kind of explain the fuse going over time vs blowing the second I turn the key on, but still sort of odd to diagnose. I also haven't seen any codes pop up regarding them for what it's worth.

You dont see any codes. Downstream heaters are indirectly tested by function- short circuit will not be seen.

Trust me... its your problem. 4.5 ohms is basically a dead short. Thats 20x specification. They dont short to the battery terminal, or even the frame. They short to the sill heat shield, and traveling through heat shields, sills, screws, frame, and everything else adds impedance.

 

[MoparMap]

Fair enough. I'll get another set coming. Thanks!

 

[Goggles Pizano]

I would check the harness.

 

[MoparMap]

I'll do a little more digging when I get the new sensors in. The engine side of the harness should all still be in the original location and tied off, but with 135,000+ miles on the car it's always possible something has moved around or chafed over the years. I did trim the heat shields and put them back over my headers to try to keep things reasonably well protected as well, but they don't cover everything or fit quite as nicely as stock. I'm also not sure if I've ever replaced the rear O2s since I've had the car, so based on just lifespan alone it probably wouldn't hurt to swap them out. The fronts I know I've done before, but figured I'd also take a closer look at their wiring and specs while I'm in there.

Once I get the old ones out I'll have to look them over closer as well. Based on what I could see under the car, the wiring is still in pretty good shape and has the braided loom still intact the full length on the sensors. No obvious rub marks or anything like that and I didn't see anything for them to rub on either the way they are installed, but the resistance values speak for themselves, so something must be up with them. I'll test the new ones fresh out of the box as well for a sanity check. I know I've probably had them uninstalled several times over the years as I was messing with my exhaust, so entirely possible I just damaged them at some point. My sensor bungs in the header turnouts are actually just anti-foulers welded into the pipe to start with, so not sure if that could make any difference on the longevity of the sensor or not.