I've run many, many miles, and outside of a few minor problems and an IP replacement at 90K, my truck has run almost flawlessly. Unfortunately, my good luck has finally come to an end. Lately, morning temps have been on the chilly side. Truck starts as she normally does (fires right off). For the first few minutes, and only while accelerating, the engine misses/hesitates. Certainly a noticeable hiccup, but by no means a lurch. No SES light. Don't have access to a Tech II so I don't know if I'm throwing any codes (unless the SES bulb is dead, a code will always set the SES light, correect?) Once the engine reaches operating temperature, she runs like a top and continues to run smoothly throughout the day.


Any ideas? Thanks.

i would have to lean toward the fuel system. how cold are your chilly mornings? the liftpump/ops system gives that "hiccup" problem, but mine wasnt when it was cold, but warmed up and at hard acceleration. jmho, im no expert on this.

How old are the injectors, original?

qm,


My injectors are the originals. Not sure I understand why this could be the problem. Engine warms up and everything is good as new. http://www.dieselplace.com/forum/smileys/Ermm.gif

Does it cough grey smoke a few times at start-up?

do a search in this forum for OPS and do the diagnostics to tell if its an ops, lift pump relay, or lift pump. sounds like you should eliminate these before throwing big money into it like injectors 'n such.

One word - glow plugs..........

qm,


I get my regular "puff" of smoke at start-up. Since it doesn't smoke a lot and that makes it difficult to really define the color (definately not white), I'd have to say that the color is leaning more to the black.


gmctd,


I changed the glow plugs before last winter. Three out of the eight were bad. Even still, I only had a hard start with white smoke with the three bad ones. Never any hesitation upon acceleration during those first few minutes. Nonetheless, I'll check them too.


lupey6.5,


I can hear the lift pump operating during the glow cycle. Would that eliminate the possibility that the relay is bad? I'm not sure, but if the OPS failed, wouldn't that prevent the lift pump from operating?

SD


SES light should illuminate with key in 'ON' position. Engine 'OFF'.


I don't believe a code will always set the SES light.


I have access to a TECH II. Coming to the Island anytime soon?





JD - Glow Plug. How many words?

if you can hear it during the glow cycle that does eliminate the relay and probably the lift pump itself. the OPS is still to be seen as after startup the ops is responsible for switching power to the lift pump. while its running open up the fuel drain petcock that is mounted to the thermostat housing with the end of the hose in something like a jar or bottle to catch the fuel. if fuel comes out and truck continues to run the ops is working, if it sucks air in and stalls within 30sec. the ops has crapped on you. if its working now check it again as soon as you can after it bucks on you. sometimes they flake out instead of just quitting

One word - glow plugs..........


au Thats 2 word there gmtd LOL http://www.dieselplace.com/forum/smileys/Big Smile.gif

Billy...any chance of you making it to the NE Diesel Get Together?


Guys...I'm not sure, or at least I don't yet understand, what would cause the hesitation to go away with the warm-up of the truck. I see that there's something, probably a temperature sensor, in the lower neck (passenger side) of the crossover. Could this be something that has crapped out? If so, is there a solid testing procedure for it and since the sensor is wired directly into a harness, how would you replace it?

Diesel's run best when they're up to operating tempatures.

qm,


This hesitation is a new thing. I don't know if it's coincidental that it started once the chilly nights arrived, but even during the summer the engine wasn't up to operating temperature when it was started, and no problems. Really then, the only difference is the cooler nighttime temps, but like I said, it could be a coincidence.


Do you think there is any danger of running the truck, towing or otherwise, while this thing is figured out?

Since we're on the subject, What temp does it go to when warm? how many miles of driving does it take to get there? thermastats are cheap insurance.


What happens when you open the air bleed on the filter while it's running?

I would LOVE to go. Especially to Lebanon Valley Dragway. That track has been good to me over the years. Even with the short shutdown area. Not a problem for you trucks though. Not unless your approaching 130-140mph. If that's the case, get on the brakes immediately after stripe.


Wife thinks I'm weird already for spending time on-line about these trucks. Way too much to do. I won't be able to make it.


Coolant Temp Sensor plays a part in the operation of the glow plugs. You can watch it with TECH II. I've read where people disconnect sensor to get extended glow cycle. If sensor is bad, might run better disconnected for testing purposes. As far as how it would affect operation of the pump, I don't know. Someone with more 'ECM in relation to Pump' experience needs to chime in.


I wouldn't think there is any danger in running/towing with truck. Monitor gauges.

The resistor (R) value of the CTS is part of the fuel/timing equation and unplugging the CTS will give the highest value and timing will advance too far/max fuel at start-up makes for a hard start. However, adding a variable resistor to this circuit seems like it would be a form of advance/fuel fooling and allow you to increase delivery/response.

Just checking to see if you guys back in the last two rows were awake......http://www.dieselplace.com/forum/smileys/Wink.gif


Sensor in the coolant crossover is the Engine Coolant Sensor - PCM uses it to give more glow when cold, among other things. Also advances cold timing........


Meaning - you may not be getting enough glow and advance for cold running, if PCM thinks engine is already at operating temps.


Wait To Start indicator should cycle more at cold start as climate cools.


Will give SES at catastrophic failure, but not if resistance has shifted but is still within range limits.


Could be oxidized connection.


The manual has resistance vs temperature chart if anyone can post it.


Remove harness connector, measure with dvm in ohms scale


SES indicator should illuminate at each IGN on, should blink once, then go off after engine is running.

If the engine is cold (air temperature, say 55* - 60*), the glow plugs will cycle maybe once after the engine has started and is running. I recall from last winter that the glow plugs will cycle maybe 2x...3x tops, during dead of winter after engine has fired off.


gmctd...I'll check engine coolant sensor for oxidation. Can this sensor go bad, and if so, how would you replace it since it is an integral to its harness?

Looked at your pic, but couldn't quite see the sensor -


Normally, you'd just unlatch the tab and pull the connector out.


Possibly yours has connection further up in the harness.


Sensor can short to ground DTC117, or become open circuit, with DTC118.


Or overall resistive value can increase or decrease, shifting temperature above or below actual, but not setting DTC


212deg is 177 ohms


104deg is 1459 ohms


59deg is 4450 ohms