7.3 idi weird problem

[9073]

hi im new to the forum and i have a question.

the truck is a 1990 f-250 5 speed 4x4 with a 7.3 diesel idi.

today i went to my feinds house about ten minutes away to pick up a ladder and it drove fine with no problems or symptoms of any problems.
on the way home the problem started happening

the problem is whenever i would step on the brake the oil pressure would drop and the engine light would go on then i would tap the accelorator and the oil pressure would jump back up to normal.
we let the truck sit for an hour and went to duplicate the problem and we couldnt get it to happen again
I think it is an electical problem
the truck supposedly has 100,000 miles on the engine
tommorrow i will go and get an analog oil pressure guage and install it

any suggestions would help

btw i checked the oil and it is fine


Matt

 

[82fordtruck]

before I got my fan clutch and new radiator put on, I had this problem, while slowing down on the interstate, especially when towing.

THe engine was running hot, and the fixes I mentioned cured it. Check the coolant temperature.

 

[highest_vision]

Welcome, Matt!
You are making a good step in getting an aftermarket gauge, the stock gauges on these are not the best and frequently leave much to be desired. Good to find out what is really happening in psi, not NORMAL
However, since you say it is dropping off (according to the gauge) at idle only, there still could be something wrong. Unlikely it would just happen like that, suddenly.
James

 

[9073]

the temperature was normal
i am also running regular rotella 15w-40 if that helps

 

[aaklingler]

it sounds electrical but put the gauge on to be safe, don't know where to point you for electrical problem though.

 

[Freight_Train]

the temperature was normal
i am also running regular rotella 15w-40 if that helps

The sending unit for the oil pressure is no more than a 3 stage switch.Zero pressure up to around 7PSI(I think but been a while since anyone was around to post it on this board) it is open showing Low pressure,7-something around 80psi it closes a set of contacts and the needle moves to a spacific point(doesn't move as long as the oil pressure is Anywhere between those points) if it gets over around 80psi it closes another set of contacts and pegs the needle.Basically,we call the stock gauges Idiot Lights with needles.They don't give you anything even remotely close to actual readings(and in the case of the Oil pressure doesn't give you any reading,a red,amber,and green light would give you the exact same effect.

 

[Magoo]

step on the brake the oil pressure would drop and the engine light would go on then i would tap the accelorator and the oil pressure would jump back up to normal.
we let the truck sit for an hour and went to duplicate the problem and we couldnt get it to happen again
I think it is an electical problem


Ok. If it is electrical (possible short in the wiring somewhere) than I would expect to see the whole dash light up, and the rest of the guages to go whacky. I think they all get their power supply from the same circuit. I could be wrong but that is my guess. If it were just the oil psi guage dropping and the check eng. light than I would suspect mechanical failure somewhere. Could be sending unit. Could be more serious. Will wait to see results of the oil psi test. Good luck. Hope its a simple fix.

 

[budtoh3zo]

Yup you should get a real gage, I had that same problem i unhooked it and never looked back

 

[Freight_Train]

The sending unit for the oil pressure is no more than a 3 stage switch.Zero pressure up to around 7PSI(I think but been a while since anyone was around to post it on this board) it is open showing Low pressure,7-something around 80psi it closes a set of contacts and the needle moves to a spacific point(doesn't move as long as the oil pressure is Anywhere between those points) if it gets over around 80psi it closes another set of contacts and pegs the needle.Basically,we call the stock gauges Idiot Lights with needles.They don't give you anything even remotely close to actual readings(and in the case of the Oil pressure doesn't give you any reading,a red,amber,and green light would give you the exact same effect.

OH Chit.I forgot what board I was on.My bad.Bouncing between here and the other place I had a temporary laps of insanity and thought I was still at The Dark Side.

 

[82fordtruck]

How do you know it wasn't hot? Where was the needle?

When mine did this, the needle was right in the middle of the guage. These trucks seem to run usually between the N and the O. Mine never goes above the N, Except towing heavy up long hills.

Basically, we are back to the stock guage thing. You don't really know what the engine temp was. Let me know where the guage rides though. That may tell us something.

 

[ramon f350]

my first guess would be the sending unit my old truck did that and when I replaced the sending unit it quit acting like that

 

[9073]

the guage was slightly past the o for temp

 

[holtzer1]

if you find it is an electrical problem...check the cluster, seen alot of shorts goin on back there.

 

[f-two-fiddy]

check your idle speed, should be 650 rpms@ idle. I bump mine up to 750 in the winter. Just to keep the alt turning fast enough to keep the heater fan running on high speed

 

[Agnem]

I was going to say... any chance your idle speed is dropping really low?