Sorry to hear the news. The money part sucks, but I'm sure in the end you'll be happier with the new motor you plan to build.

Though 18psi is lower than what you should have at idle, one thing for everyone to keep in mind is that the factory gage will usually always read a slightly higher psi (unless the sending unit is going out) than a more accurate mechanical aftermarket gage.

 

That was the case. The stock gauge ran about 5 psi higher than the mechanical one.

 

So, is the sending unit in the factory gage itself? Or is it located outside of it? If it is outside, wouldn't that also void the other oil pressure gage?

I haven't had the car enough to look at the oil pressure after opening up the throttle. But I am going to be one un-happy camper if my new LS1 needs a new motor. A new sending unit won't be too bad, but I definatly can't afford a rebuild right now. Are sending units common to go bad?

 

Sending unit is behind the intake, separate from the gage.

Is your at-idle oil pressure always at 20-25 as soon as you hit operating temp? Or only after extended idling and/or other harsh conditions?

What is the oil pressure at 2k rpm? And 3k rpm?

 

Like I said, I haven't gotten a chance to drive it much since I bought it so I don't know much about the pressure at different RPM's just yet. I'll be driving it in the next few days, so I'll let everyone know then.

I do know that at cold start up, its just under 50, and then once its warmed up, it sits at 20-25 at idle. I also haven't had a chance to change the oil yet, or the oil filter. When I do, I'll be stepping up to a M1 oil filter which should help increse the pressure. I will see if the pressure increases with the throttle once warmed up.

 

and bada boom goes the motor at 20 psi

 

CALL911, I guess you have an lt1 correct? I'm not sure but I think they tend to idle with less pressure and have lower pressure across the board compared to the ls1. If you do have an lt1 the sensor is in the front near the trottle body (I think, don't qoute me on that).

RPM, at 2k the o/p is about 35-38 and 4.5-5k rpm the o/p is around 45 psi. The part that really makes me worry is that going down the higway at 2k rpm wit ht/c locked up, the pressure varies about 8 psi when I play with the gas peddle, NO CHANGE IN RPM

 

This is in reguards to my newly purchased 98 LS1 car.

I'll start to worry more when I have a good filter on it and after given some throttle it stays down there in that range.

If a good filter and an RPM increase brings it up to the 50 range, I won't be too concerned.

 

Let us know the pressure readings at higher rpms once you take note.

50ish at cold idle is fine. Most are 50-60 at that time.

If it's always at 20ish just as soon as you hit operating temp, even in the cool March weather, that might be cause for concern. But again, I'd first make sure that the sending unit wasn't the issue before getting concerned about the motor.

 

45ish is too low for 4.5-5k rpm. And an 8psi drop under thottle is not good at all.

 

How much are the sending units, and where can I get them?

 

gm dealership....60-80 bucks...youll need a pretty large socket also to fit over it

 

are sending units a common prob on 98s? i have a 98 Z, with the same sort of low psi, but never really gets below 30. the thing that strikes me odd is that the gauge is usually playing catch up to the revs when you gas it a little. the car never really goes more/less than 30-45 no matter what

 

Well, I was going to drive the car today to check it out further, but then after a few days of 70 degree wheather, it decided to dump 4 inches of snow mixed with freezing rain and ice . As soon as it clears up, I'll go check it out.

 

Not that I know of.

30-35 psi at hot idle (A4 idle speeds) is not a problem, IMO.

But, what concerns me is when you mentioned that it never goes past 45 at any rpm. Not even at WOT?

 

Give us some more details when you can.

 

ummmm, I would have to check, I only really realized how low it was getting today. The morons at a shop I had to take the Car to(for importing), idled it for I would say upwards of an hour, when I got the car back the low coolant light was on, and the car was really hot, probably almost at mid mark. Anyways I drove the car home after a decent sized battle with the service manager and the oil pressure was fairly low the entire time, it has been a lot lower than what Im used to in the TA. But I believe when up to 3k rpm it maybe got high 40s/50s. I will maybe give her a run tomorrow, but should I go WOT with that low pressure, like under 30 for idle?

 

30 is a bit on the low side for the stock M6 idle rpms (800 for M6, vs 550 in gear/650 in park for the A4). But after an hour of idle time, pressure will usually drop a bit lower than normal, especially if the oil is a brand on the thinner side of it's rated weight. Mine, with an A4 idle speed, is usually at about 35 once fully warm, unless I idle the car for a long period of time. Then it'll drop to 25-30, but recover to 35ish after driving around for a while.

If you're seeing 50ish psi at 3k rpm, I would not be too worried. Maybe do an oil change with an oil that does well in the LS1 (like GC 0W30 or M1 0W40) and see what the idle pressure is.

 

some 98s DID come with crappy pumps though....

 

Yes, a small amount of '98-'00 LS1s had factory pumps that failed, but those bad pumps usually resulted in a sudden and instant loss of all oil pressure with no real warning signs prior, then full pressure recovery after a restart, but the damage was already done. Or at least that's how it went for the one guy that I knew it happened to, and the few others that I've read about.

Not a common problem though.