Engine/Transmission (1994 - 1998) Help: Oil pressure drop off at idle

[JGK]

Suddenly, in the last few days, my oil pressure gauge drops to 0 and the check engine light comes on and chime rings while sitting at idle. This happens only after the engine is fully warm.



I did a search here and I'm aware of the TSB that reflashes the PCM to change the parameters of the gauge so that it fools it to thinking it is reading a bit higher pressure. But I don't really want to fix the symptoms.



I also found a few owners had success by changing the sender, but several said it didn't help or last long.



I intend to change the oil & filter (oil level is fine, BTW) since its due, and change the sender to see if that will fix it.



However, my question is, has anyone who has experienced this found another reason for it and a solution that actually fixed it? My only other thought is the oil pressure relieve valve, which may be allowing oil to get past. I believe that is found in the oil heat exchanger cover (the assembly on the side of the engine where the filter screws in to).



TIA,

-Jay

 

[gtwitch]

just bought a 96 and has low pressure at idle was going to post this we will hope someone has some suggestions!



gtwitch in Wyoming

 

[Vaughn MacKenzie]

Jay, it might be good to check the pressure with a mechanical gauge there at the filter head just to be sure. . .

 

[JFaughn]

Test , test , many things can cause this , after testing them figure how to fix .

 

[Eric_B]

I had been going thru the same thing with my 96 and likewise only when warmed up ,at idle,in gear,light on and gauge at zero. My idle speed was also ok, about 800 rpm in gear. Checked with a mechanical gauge cold and hot for a couple of weeks , everything was fine pressure wise even on a way overdue oil change. Never went below 32lb. I recently had a new oil sender installed that I bought from the dealer and all is well again. The gauge still does not respond or have range of motion like a true mechanical gauge but I don't expect it to being PCM controlled.

 

[JGK]

I ended up replacing the sender. That fixed it. I checked the pressure at the filter with a mechanical gauge and that showed good pressure, so I figured it had to be the sender or dash gauge.



A friend with a '98 auto started having the same problem about a week after I did. A new sender also fixed his problem.



I feel fortunate that mine's not a 24 valve. The sender on those is like $250 form the dealer! Wheeeeeee!



-Jay

 

[gtwitch]

oil pressure problem

Thanks for the suggestions, I thought that this might be the problem and I will try and get the guys to let me have the truck in the shop sometime next week and I will replace the sender and change the oil and filter. I willpost the results. Thanks to all and to TDR for this forum.



gtwitch in Wyoming

 

[JSimoneaux]

I've recently started having the exact same issue with my 98 12 valve. Anyone have the part number for the sending unit?

 

[Bobcat698]

Its probably a sender. . I have a electronic oil pressure gauges on both my 96 & 98 and both show that there is good oil pressure, even when the 98 drops down to nothing.

The 96 truck shows much higher pressure on an electronic gauge than the dash gauge. 45PSI on the dash is usually 60+ on the electric gauge.
I was actually concerned with the "low reading" on the dash when I first bought the truck. . Not anymore since I put the real gauge on.

 

[FrostG]

I assume that the TSB that JGK is referring to is #08-22-99. I got the impression that rather than change the whole calibration curve that his change was to reduce the pressure point at which they chose to show no pressure rather than the actual pressure. I have been planning to find some dealer that will perform that upgrade for a fair price since my factory gauge drops to zero at a point just below 30 PSI by a mechanical gauge. My nearest dealer wants to charge me $100 to do the TSB which seems a little out of line but the next nearest dealer hasn't even returned my calls. If I am out of touch about the cost for the program upgrade please let me know.



FrostG

 

[JGK]

Follow up...



Since the temps have gotten hot here lately (mid 90's the last few weeks, 102 to 107 the next few days), the problem is still ocurring now and then, more often since getting hot. Usually it happens when I do a very easy take off from a stop where I virtually let out the clutch from idle. So I'm still wondering if there isn't another issue.



A friend has a '98 12 valve auto and his started doing it. He replaced the sender the other day and its still doing it, almost worse in his opinion.



So we broke out the service manual and looked at the oil system. There is a bypass valve in the oil filter mounting assembly (I mentioned that in my original post) and we're wondering if that is experiencing fatigue much like the fuel bypass valve on the side of the inj. pump. I think you can remove it by simply unscrewing it from the mount. It appears to be just forward of the oil filter near the top of the filter - a big hex-head plug. If either of us take it out and do anything with it I'll post with the results.



If the TSB in fact simply alters the point where the gauge chooses to drop to zero and the chime goes off, that may be an effective solution since it appears there is no oil pressure problems once off idle. But if replacing or fiddling with the bypass valve will raise the idle pressure slightly, I'd prefer that approach.



-Jay



P. S. Just notice the thread by JGheen regarding this bypass valve. As expected, it appears this valve will only affect max oil pressure, not necessarily idle pressure. May have to look closer at the TSB, but I don't really want to spend another $100 to have the dealer do it!

 

[JSimoneaux]

Follow up...

Since the temps have gotten hot here lately (mid 90's the last few weeks, 102 to 107 the next few days), the problem is still ocurring now and then, more often since getting hot. Usually it happens when I do a very easy take off from a stop where I virtually let out the clutch from idle. So I'm still wondering if there isn't another issue.

A friend has a '98 12 valve auto and his started doing it. He replaced the sender the other day and its still doing it, almost worse in his opinion.

So we broke out the service manual and looked at the oil system. There is a bypass valve in the oil filter mounting assembly (I mentioned that in my original post) and we're wondering if that is experiencing fatigue much like the fuel bypass valve on the side of the inj. pump. I think you can remove it by simply unscrewing it from the mount. It appears to be just forward of the oil filter near the top of the filter - a big hex-head plug. If either of us take it out and do anything with it I'll post with the results.

If the TSB in fact simply alters the point where the gauge chooses to drop to zero and the chime goes off, that may be an effective solution since it appears there is no oil pressure problems once off idle. But if replacing or fiddling with the bypass valve will raise the idle pressure slightly, I'd prefer that approach.

-Jay

P. S. Just notice the thread by JGheen regarding this bypass valve. As expected, it appears this valve will only affect max oil pressure, not necessarily idle pressure. May have to look closer at the TSB, but I don't really want to spend another $100 to have the dealer do it!

Jay I just took my 98 12 valve in on Tuesday to have the flash done and they wanted $100 even after it didn't fix the problem. The service jerk had the nerve to tell me "you really should let us diagnose the issues with your truck and stop reading the internet trying to fix it yourself". I was livid and I spoke to the service manager who eventually gave me my keys and told me to take my truck. I took it home and put in the 3rd sending unit in a month and it seems to be working great. I did install a mechanical gauge on the filter housing so I can see what's really going on.

All of the sending units came from the parts. department of that dealership except for the last one which I bought from NAPA. My next step is Cummins if this one doesn't work.

 

[JGK]

I tried to get one through Cummins but they don't carry it. Since it has to work with the Dodge electronics, its a dealer (or aftermarket) only item.



Thanks for the info on the reflash. We have some pretty reasonable dealerships around here (my personal experience) so maybe I'll get lucky. And we'll really take to heart his advice about avoiding the internet Yeah, right.



-Jay

 

[JSimoneaux]

I tried to get one through Cummins but they don't carry it. Since it has to work with the Dodge electronics, its a dealer (or aftermarket) only item.



Thanks for the info on the reflash. We have some pretty reasonable dealerships around here (my personal experience) so maybe I'll get lucky. And we'll really take to heart his advice about avoiding the internet Yeah, right.



-Jay

The sending unit I have in it now is made by BorgWarner, seems to be working well.

 

[Coalsmoke]

Guys, maybe I'm missing something, but these sending units you guys keep buying can't be cheap. If the factory ones are this problematic, then what about just putting a proper oil pressure gauge in the cab of the truck and calling it done? A decent quality one can be had for $50-75 plus a bit for hardware. I guess the only problem might be figuring out a way to wire it up to a chime.

 

[Coalsmoke]

I'm not sure what this unit costs, but it has a built in alarm and wiring provisions for an ignition.

CruzPro OP60 Digital Oil Pressure Gauge and Alarm

 

[JSimoneaux]

Guys, maybe I'm missing something, but these sending units you guys keep buying can't be cheap. If the factory ones are this problematic, then what about just putting a proper oil pressure gauge in the cab of the truck and calling it done? A decent quality one can be had for $50-75 plus a bit for hardware. I guess the only problem might be figuring out a way to wire it up to a chime.

The sending unit that I have in there now was $30. I already have a mechanical oil pressure gauge that I'm thinking about moving to the cab but if you don't fix this problem your stock gauge will stay at zero, the truck's chime will sound and the red "check gauge" light on the dash will stay on. With it already on you don't get that alarm if something else like temp were to set it off.

 

[MFalkinham]

I had the TSB done just to get rid of the annoying chime at every stop sign. I also have a mechanical gauge and it always showed good pressure even when the factory gauge would drop to zero. Putting in a new sender doesn't solve the problem (I tried it). I think it's a computer software glitch rather than a mechanical problem, and the TSB is their band-aid to stop the chime. Good enough for me since I have the mechanical gauge to verify. If I remember correctly I was charged about $90 for the TSB.

 

[fest3er]

I tried to get one through Cummins but they don't carry it. Since it has to work with the Dodge electronics, its a dealer (or aftermarket) only item. ...

Nope. The Cummins part for my CPL is 3932300. I recently bought one, and he told me that's the second they ever sold. They sold other one in 2001. To me. That it lasted six years and 140K miles says something about it.



It cost about $33, plus $15 for overnight shipping from the factory.



Get the engine number off the plate (left/outside side of the timing cover). Cummins will use that to look up the correct part for your engine. But I'll bet they're all the same: 3932300.



N

 

[JGK]

fest3er,



You are entirely correct! I noted the part number and called my local Cummins Northwest shop. My regular contact guy there looked up the number and confirmed it was an oil sending unit for my engine. Apparently the day stopped I in to try to get one, the guy I talked to (not my regular counter guy) didn't know they may be available for some motors (like mine).



So, yes, using the serial number or CPL number on your engine, your Cummins dealer may be able to come up with a sending unit.



By the way, my local shop quoted a price only a few dollars different than the dealer.



Thanks,

-Jay