Oil Pump???

Alright, I've researched the hell out of this oil pressure problem I'm having, and nothing is working.

I put in a non-Fram filter, I changed the oil pressure sending unit, I'm running Mobil 1 10w30 synthetic, and some SeaFoam additive... nothing. The guage is still reading zero pressure when I come to a stop.

I found one thread that hinted toward changing out the oil pump. However, wouldn't an oil pump just go bad, and not just kinda' work? When I excellarate the guage works (not well) enough to register some pressure. If an oil pump is suggested are there any tips for me? Thanks.

1997' XJ Sport

At some point in the 90's jeep started using aluminum oil pumps, have heard of a few owners having them self destruct. The Mobil-1 is probably whats saving your ass if it is weak. Put a mechanical gauge on it the engine, remove the stock sender and put SW or autometer on there so you get a real picture of whats happening. Never know, could be a wiring problem leading you down the wrong path...
I just replaced my engine with a jasper reman, came with a meling cast iron oil pump according to them..

From jaspers site
--Low oil pressure is an inherent problem with this engine. To
remedy that problem, JASPER is using new design cam bearings to
improve oil pressure. Along with that, a new Meling cast iron oil
pump is used. The original oil pumps were aluminum and the housing
would experience severe wear. This pump is more durable, providing
longer pump life.
--To reduce noise within the timing components, a silent chain is
installed.

What richp said. I wouldn't run/ drive with 0 oil pressure at idle. Period. Any engine noise? No oil pressure should cause lifters to make all sorts of racket--first sign your "out" of oil. Second sound would be rod bearings. Last sound, well, you don't want to go there! Put a mechanical gauge on it--screws right into where the oil pressure sender is mounted. 1/8-inch pipe, I think. Worn cam bearings will kill oil pressure--and then the engine!

Ok, I've read previous posts about the mechanical guage. Where can get one... regular autoparts store? Is this a universal tool, or Jeep specific? Thanks.

ps- there's no engine noise (just a very quiet ticking to be expected from 110,000 mi. engine)... I hope it's just the guage telling me lies.

Any parts place should carry generic mechanical oil gauges good for 60psi. By the cheapest one--no need to pay for fancy, back-light unit--just the basics.

Check auto parts houses that deal with a lot of area shops, or that share space with a machine shop, if you want a "diagnostic" gage.

SW (Stewart-Warner) or other high-end gages should be easy enough to order - but try dealing with a smaller shop, rather than a chain store.

The hole where the sender goes is 1/8" NPT, and that is the thread that is on most "diagnostic" gages - even though they come with adapters for those wonky metric threads that the Japanese like to use, and some English BSP (British Straight Pipe) threads as well. Make sure you have the engine OFF when you are removing/installing the sender (I probably don't need to tell you that, but I should put it out there anyhow!) so you don't blow all your oil out and kill your engine.

Once you have the gage in place, you can check the oil pressure directly at idle, and at speeds by manipulating the throttle by hand. If you have a helper you can trust and a tach, you can get a better picture of what's going on in there.

I've taken the idea one step further - since I do quarterly inspections anyhow, I've "T'd" in a shut-off style quick-connect, and screwed a mating fitting onto my standalone gage. I can connect and disconnect the gage with the engine running, and not have to dork around with pulling the sender.

The sender should be near the base of the distributor.

Expect to pay $30-40 for a quality diagnostic gage - I haven't priced kits for add-on gages recently. A diagnostic gage will come with a heavy-duty rubber hose about 2-3 feet long, so you can hook it up and have it out of the way when you start the engine. Lisle and K/D Tools make decent units - see if you can find those.

I don't know why anyone would want to make a pump housing out of aluminum - I think that's what happens when you get accountants involved in engineering decisions. Any engineer would know that the pump would wear out quickly! I'm not even an engineer yet, and even I know that...

5-90

Great info.... thank you. I did know about turning off the engine, but the more details the better... because there were 10 other things in your response that I did not know. So, thanks again... everybody. I will buy the gauge and check.

Is there anyone out there that knows what years they used the alluminum oil pumps?

97' XJ.

They didn't have a guage at Autozone, but I'll check Napa, and O'Reilly's tomorrow.

Just after start-up I have normal oil pressure (45-50psi)... then at normal temp and about 1,500 - 2,000rpm the pressure is about 13psi. After driving for about 10-15min. I will come to a stop and idle... 0psi.

I know the guage will help, but maybe these numbers sound familiar to someone.

:repair:

?!?

Idle spec for the AMC242 is something like 12-15psig at idle, the number usually given is 13. I'm inclined to think it should be around 35-40psig at 3000rpm, but I'd have to look that one up.

5-90

Oil Pressure may be lower than spec due to wear, if you have 10 PSI at idle with the motor/oil at full operating temp, you should be alright, although its not good. If you have less than spec oil pressure, start trying to identify the problem, hopefully a new oil pump may get it back up to spec, but the most likely cause of low oil pressure is wear all over the motor and a rebuild is in order.

I've heard figures of 7 PSI at idle, not sure if I agree that 7 PSI or better at idle is acceptable, but if you below 7 PSI at idle, time to give it up and rebuild the motor (Unless its just the oil pump and a new one get you back up to spec).

A compression check is a valuable tool. If you fail a compression check and you have less than spec oil pressure, thats a good indication that you have a badly worn motor.

:bawl: Alright, it's confirmed that my in dash gauge was correct. I ran the machanical gauge with the same result. At start-up = normal oil pressure.... then at normal operating tempature at idle it drops to zero. When I accelarate = almost normal, but still a bit' low.

I guess I will start with a new oil pump, but I will get a compression test to see if it's a lost cause, and I need a rebuild..... any other input?

97' XJ Sport, 110,000mi.

ODXJ97 said:

Just after start-up I have normal oil pressure (45-50psi)... then at normal temp and about 1,500 - 2,000rpm the pressure is about 13psi. After driving for about 10-15min. I will come to a stop and idle... 0psi.

Click to expand...

The oil pressure when the engine's cold is too good for the problem to be a worn oil pump or a stuck open pressure relief valve, especially with a lightweight synthetic oil.
The large drop in oil pressure to almost zero as the engine warms up is a classic sign of excessive bearing clearances i.e. worn bearings. Rod bearings usually fare the worst followed by the manins and the cam bearings.
Before you remove the oil pan and start replacing stuff, check the compression on all cylinders. It should be at least 120psi with all cylinders being within 10% of each other. If you're losing compression past worn rings, you'll be looking at a complete rebuild anyway (might be an opportunity to build a stroker).
If the compression checks out OK, remove the oil pan and replace the oil pump, rear main seal, and rod/main bearings.