Surging/ Slight Cutout under load

[seth_95]

My 6.5 started cutting out today. I was heading up a hill. pretty step one and it started sounding and feeling like it was cutting out. Also I have noticed that there was alot of black smoke also. I have just replaced the fuel filter about 2 weeks ago and I have gone about 250 miles on this tank of fuel. It seems to do it under heavy acceleration and it has done it once under normal driving. There is only 40k on the IP and 200 miles on a new PMD.

[More Power]

Lift pump generating fuel pressure? ;)

Jim

[Turbo Al]

Oil pressure switch sending signal to Lift pump?

[seth_95]

well my oil pressure guage shows oil pressure. I can hear the lift pumpo operate. How to I check the lift pump pressure?

[moondoggie]

Good Day!

"I can hear the lift pumpo operate." This tells you one thing & one thing only: your lift pump makes noise. It in no way tells you if it's working or not.

Your LP is powered by two circuits: relay during cranking, & the OPS during running. Boy, are you blessed. It's REAL easy to check the cranking circuit on this truck; too bad this only works on 95's (I asked some time ago, it really only works on 95's).


Crack the fuel filter nut (black plastic round thingy on top of the fuel filter housing) a little. Connect a piece of tubing to the port on the top of this nut; drop this in a container.

Set the parking brake or block the wheels. (Maybe better to not use the parking brake on a vehicle you don't know - maybe it never releases, eh? ;))

Put the tranny in any gear EXCEPT park or neutral.

Turn the key to the crank position - the LP will run, but the engine will NOT crank.

Wait for a solid stream of fuel to be pumped out of your piece of tubing. If not, LP system isn't working.

Checking the OPS is a little different: While idling in the driveway, slightly loosen the black plastic nut at the top of your fuel filter. If it squirts fuel, your LP is at least working; if the engine almost immediately dies, it's not. (You're almost certain to have a REAL hard time getting it started again if the second condition exists. The fuel just ran backwards down the fuel line towards the tank, & unless you fix the LP system B4 running this truck again, your IP is going to have to pull the fuel from the tank.)

Let us know &...

Blessings!

[DaveNY]

Maybe a little burp in the vacuum solinoid causing temp loss of boost and resulting loss power and excess smoke? Any codes or light?
Dave

[seth_95]

the check engine light has been comming on for about 5 seconds then shutting off. It doesnt matter if its idleing or going down the road. The dealership wants to charge $50 to check the codes! Does schucks check codes? I just bought a new wastegate solenoid today, well see if this fixes it.

[JohnC]

You can check the codes yourself. Look here (http://www.thedieselpage.com/members/trblcode.htm) if you're a DP member...

[oneton]

Seth, it's funny that you posted this problem, I was just going to post a similar problem until I read yours. Mine is slightly different but may shed some light that'll help us both out. So here's my situation;


After leaving the truck sit for a couple of weeks the truck will fire up just as it should but die shortly afterward, about 8 sec. later. It'll take some cranking but it'll fire up again and run normal. This doesn't happen when I get in the truck every day. Only when the truck sits for extended periods of time. But even though she starts up fine I still have the little burps while driving down the road like she's getting ready to cut out. It'll also happen under hard acceleration but not all the time. I just pulled a hill today ( no load ) boost was fantastic, around 10# spike and leveled out at around 8lbs, and didn't hesitate at all. That's the good news but during normal driving power seems a little flat. I don't know if that's just from driving the D-max for the last 4 and half years though. But I seem to recall a little more snap in the motor before I parked it all those years ago.


I hope this will shed a little light on both our problems that sound pretty close.

On edit, I should also say I'm not getting any smoke ( not even a hint ) or SES light.


David

[seth_95]

Well I read the codes and I have a code 16. Which is the vehicle speed sensor fault, which I knew that one already because my abs light is on because my chains rubbed through the wire. I bought a new wastegate solenoid today $41.00. Try putting it on tomorrow if its not snowing. Tested the lift pump by cracking the bleeder valve and turning the key while truck was in drive and it squirts plenty of fuel out at a good constant rate.

[seth_95]

The problem I am describing is more like a fish bite type of cutout. It happens more under a load or medium throttle and at times WOT. I have heard this can be caused from the optical sensor filter harness that was prone to fail with OEM harness. Could this cause this to do it? If so where do I get something like this?

[JohnC]

Do the fuel pump test while the engine is running to get the full effect. Testing it with the key to start skips the oil pressure switch.

The optical filter can be removed for testing. It's plugged in line with the optical sensor. The truck will run fine without it.

[moondoggie]

Good Day!

"Tested the lift pump by cracking the bleeder valve and turning the key while truck was in drive and it squirts plenty of fuel out at a good constant rate." As stated, this only tests the LP system during cranking. It's valuable - at least you know your LP works - but it doesn't tell you if it's getting power thru the OPS during normal operation.

If your problem feels almost exactly like a gasser with an ignition miss, far & away the most likely problem is LP system, which in your case would be OPS and/or assoc. circuitry. But why guess? Test it, or at least figure out a way to provide power directly to the LP, effectively bypassing the OPS, & take 'er for a drive. (I'm WAY too cheap to buy parts that are this easy to test.)

"The optical filter can be removed for testing. It's plugged in line with the optical sensor. The truck will run fine without it." 10-4. You can even temporarily disconnect the IP optical sensor & drive the truck - it will run in a default mode. If the problem doesn't change much, likely your IP optical sensor & assoc. circuitry is OK.

Blessings!
(signature in previous post)

[rjwest]

You sure could use an in dash mounted fuel pressure gage,
makes trouble shooting much easier

[seth_95]

Well I tested the vehivle today while the engine was running. I hooked a preesure guage to the top of the air bleeder valve and opened it up while the engine was running and it read zero. The truck didnt take long for it to die.

[sailun]

I had the smoke, low power and code a bit earlier this year, also. Since I had seen this before at about 80k, I disconnected and re-connected the plug to the solenoid, and shook it around a bit. No more smoke, so I re-set the code.

I have read other posts which also refer to an intermittant solenoid problem.
Hope yours is fixed.

[DmaxMaverick]

Well I tested the vehivle today while the engine was running. I hooked a preesure guage to the top of the air bleeder valve and opened it up while the engine was running and it read zero. The truck didnt take long for it to die.
If the lift pump operates and builds pressure with the "engine off/key on/out of P-N procedure", I suspect you have an OPS problem. This can/will cause most of the issues you have been fighting. Put a volt meter on the LP wires (still connected to LP) and monitor the voltage during a normal start cycle. If you see voltage during cranking, then none after the engine is running, your OPS or OPS harness has failed. Either the switch itself, or wires/connectors. No or low oil pressure will also cause this, but you'd have other problems, too.

[moondoggie]

Good Day!

When the OPS quit in my daughter's 89 (see signature), it was partially open: it was providing ~ 8 or 9V to the LP, which wasn't enough. As stated, OPS failures are common, at least common enough that we're aware of them here on the Page.

Blessings!
(signature in previous post)

[seth_95]

How hard is it to repair? Could this be why it is also hard to start all the time. Doesnt matter if its warm or cold? After it died when I did the last test, I had to prime the filter and it has started the best it has ever had.

[moondoggie]

Good Day!

"How hard is it to repair?" A bit of a pain, I guess. It's at the back of the engine, almost against the firewall, if memory serves. I think I had a deep socket that fit, but can't remember for sure.

"Could this be why it is also hard to start all the time. After it died when I did the last test, I had to prime the filter and it has started the best it has ever had." As described above, your LP is powered through a relay during cranking; you have tested & found this works properly, That doesn't mean, however, that the LP not working during run isn't having some effect on the subsequent start-up.

"Doesnt matter if its warm or cold?" I don't think so.

Blessings!
(signature in previous post)

[seth_95]

Well I replaced the oil pressure switch this evening. My guage now reads about 40 ad idleing and then moves to about 60 while driving. Seems fairly high to me. I checked my fuel pressure and it now reads about 4psi. The fish bite is now gone! Thanks for the help. I am glad to have this problem gone because I was getting nervous about driving it lond distances.

[JohnC]

Just FYI, the oil pressure sensor performs 2 separate and disinct functions. One is to drive the gauge and the other is to power the lift pump. Performance or failure of one function usually has no effect on the other.