Two weeks ago my 95 blazer was haveing a misfire an low power issue. Later that day I noticed my oil pressure broke the gauge. I found out one my spark plug wire poped off an fixing that resolved the misfire. However the oil pressure when starting cold will read 40 an with a lil acceleration jump past 80 the max number. Once she warms up it tends to read normal setting at about 5 for idle an 40 when about 2500 rpm, if you gun it about 3500 then go past 80 again. I been trying to troubleshoot so I can determine what could cause this. The truck runs fine starts fine although I noticed last night the engine remained hot for several hours when my friend trucks were cool. However coolant sensor doesn't seem to show overheating... Anyways I'm confused. I think it could be a oil sending unit but they tend to read 0 when they go bad not go over 80 so I herd. Got 231k miles starting last night lol. If any one has any thought please let me know. Thank you.

 

 

Could be a few things:

Faulty oil pressure sending unit, wiring, connectors, dash gauge
Malfunctioning oil pressure relief valve
Blocked internal oil passages
Wrong oil viscosity (not likely since its jumping around)

Best would be to verify with a known good mechanical pressure gauge to determine if its really high pressure or the gauge circuit.

George

 

Thanks for the response. I'm not a expert DIY guy but I been learning more an more. But like most trucks to test the oil pressure you thread the pressure tester were the sending unit is threaded in, but to do that don't you kinda have to get the distributor out of the way? I hate sounding lazy but in Florida with the heat an trying to get back there is a big pain. I mean I'll get around to it but I'm just trying gather much info as possible before I drive into something.

 

I've been dealing with this exact problem for the last year. I'd just replaced the sender a year or so ago with a NAPA unit, so thought something was plugged, or my bypass in the pump was stuck. Couldn't have been the sender.

Anyway, went to change the worn out distributor, so was able to order an A/C Delco sender, and changed it out too. Pressure reads great now.

I had your symptoms. From engine start, it pegged, then a few miles down the road at stop lights it would be normal. But any acceleration and it would peg.

Now it's 70 on start, creeps up to 75 on acceleration. Then drops to 60 on warm up and 50 or so at stop lights.

Good luck

dviles

 

Thank you for the feed back. Just ordered a sending unit seeing as how I need to mess with it regardless. We shall see how it works when that time comes. But ya good luck indeed lol. Thank you again.

 

If you are reluctant to remove the distributor to access the sending unit then about the only thing you can do is access the contacts on the back of the sender and measure the resistance values and see if the output really pegs. You would only isolate the problem as either the sender/actual engine oil pressure vs the wiring, connectors and dash gauge. I don't know the resistance values across the functional range on this sender, maybe someone can help with that. Another option might be to tee into an oil line somewhere with a fitting and a second access point but I have not looked around to see if there is a spot that could work. That would be as much work as the distr I would think. The last option would be to use the adaptor that screws in to the oil filter threads and allows attachment of a second gauge. Something like this:



If you really do have engine oil pressure problems this needs to be addressed because severe engine damage could result. The proper way to do this is the mechanical gauge route to verify.

Maybe someone else has other ideas that I have not thought of.

George

 

​​​​​question about moveing the distributor I'm assuming you would undo the sparkplug an coil wires to get better access to removing the distributor. Once I do that an once I get a oil pressure gauge I undo the oil sending unit hook that up then I would have to put the wires back on the distributor to start the engine an then check the oil pressure?

 

Sure sounds like a faulty oil pressure sender to me.....actually a common failure. And yeah getting to it is a PITA.. Has to be on a cold engine. I am not sure the sender can be changed with the distributor in place or not....have never tried on the Blazer. Usually the sender internal oil seal fails, oil gets inside and shorts out....pegs the needle....then the oil drains out with the engine off, start engine again, sender works for a few minutes and then fills with oil...cycle repeats.

Good luck with it.

 

You can either go for a replacement sender as Lanny suggests or hook up a mechanical gauge first to confirm. This guy gets to the sender without removing the distributor:


George