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Low pressure at idle after rebuild

Hi pelican people,

I am rebuilding, by myself, my 3.6l engine from my 1990 c2. This is my first rebuild. I am running into a pressure problem that puzzling me and direct me into splitting the case again, which is the last thing I want to do. I used mobile 1 15w50 al the time.

The problem is I have low pressure at idle , around 0.75 bar on the dash gauge, but soon i am give higher rpm the pressure goes up roughly 1 bar / 1000 rpm. Before tearing the engine apart everthing was normal, i had to open the engine because two head studs bolts had undo.

Things I have performed and changed:

-I followed Wayne's book method of assembly.
-Case was hot bath clean, clean by me afterward until you can heat on/in it.
-All parts were cleaned using varsol and brake cleaner when possible.
-During dessambly everthing, I mean everthing, was pictured, put in bag and labeled in order to help me during assembly.
-I measured, crankshaft, connecting rods, case, rocker arms, rocker arm's shaft and everthing was in specs. ( i am a machinist, therefore know how to use properly measuring tool).
-Installed new crankshaft, connetcing rod, intermidate shaft bearing that a compared with old one before installed and were all similar within a 0.001" ( accuracy of my vernier)
-Used vector reinz gasket set with green pump seal and blue case thru bold o-ring.
-Everthing was torque using porsche factory manual.
-New nut was used on the case perimeter and used 574 to seal the case.
-The pump was remove from the case, empty from the oil by gravity, placed in a box until reassembly.
-New 102 mm J/E piston with Mahle cylinder, new matching Gotzie ring.
-Reground cam shaft to 993 supersport specification.
-993 H/E with rerouted scavenging line in A/N 16 and a Setrab ( m22 to #16 A/N) fitting in the case.
-Complete head work done by a locale porsche experimented shop.
- RS fan hub.
- Supertec head stub hardware, ARP connecting rod bolt.
- New custom Steve Wong chip.

This is where I think things can be wrong:
- Pressure sender deffective, which I eliminate because reading are similar using the old one.
- Oil pressure relief pistons in the case, I took them out in everthing was according to manual.
- RS hub, which make the alternator run slower, combined with a worn alternator could not generate enough voltage at idle.this is my next thing to do, I will check the pressure with a manual gauge from the case directly to eliminate this one.
- Setrab fitting or A/N line causing problem.
- Pump sealing ring wrong or pinched during installed.

I need some advices or comments to make this work. Thanks in advance.

Here a few pictures to help, sorry for the order:
Also note that number on piston does not match firing order was for weight measurement only.











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Last edited by pat_thonon; 03-29-2013 at 02:02 AM..
Old 03-29-2013, 01:55 AM
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KISS.....Verify the reading !
2 -if all clearances are correct..it has to be in the pressure management section
Old 03-29-2013, 03:20 AM
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I had similar problem, years ago, and pulled it back apart and o-ring for the oil pump had slipped out during case assembly.
Old 03-29-2013, 04:33 AM
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Sounds like you've considered a lot of the potential sources already. Only thing I can add is recently a guy on the forums had a similar problem. Turns out the paper towel he used to plug the pump inlet while working on the engine was still in there! Yikes. Disaster averted.

Prime oil on rebuilt engine
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Old 03-29-2013, 09:22 AM
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I just went through a similar problem with my rebuild.

When you put the rod bearings in did you check for proper clearance?

When you installed the tensioners in the chain housings did you confirm the oil hole is pointing toward the cap on both sides (i.e., away from the chain). You can confirm this by removing the cap. Also, confirm you put the right tensioner on the right side, left on left side as they are different (both of these errors are common during rebuilds, ask me how I know). Check your pictures, maybe you have a shot of these after install.

Be careful as to how long you run the engine. I am assuming you have not done the break-in procedure (2000 to 2500 RPM for 20 minutes). If you run the engine at idle for too long it can potentially screw up the camshaft/rocker break-in. Run the engine as little as possible before you solve this.

Check the oil pressure with a manual dial gauge. While it is unlikely that BOTH of your senders are bad, it is possible.

When you removed the rockers did you clean out the oil holes? Sometimes these can get blocked.

This can be discouraging. Keep at and you will eventually find the problem. Good luck.

Last edited by Green993; 03-29-2013 at 12:00 PM..
Old 03-29-2013, 11:42 AM
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A - Left-hand chain tensioner. Oil supply hole hole points up.

B - Right-hand chain tensioner. Oil supply hole hole points down.

Note

The spring retainers are additionally marked with „oben" (top) and „unten links" (bottom left) or „unten rechts" (bottom right).
Old 03-29-2013, 11:47 AM
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Here is a diagram of the oil system. Solid lines represent oil under pressure. I found this helpful in understanding how the oil system works.

Old 03-29-2013, 11:54 AM
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A couple more things:

1. Check the 2 oil hoses that go to/from the engine to the oil tank. Sometimes these can get crushed or maybe a rag was left in there, both of which would cause pressure problems. This is a tough one - perhaps do this last because you will have to drain the oil. But if you get to the point of tearing it down again, you'll have to do this anyway. Hopefully not.

2. Did you do anything with the lines to the oil cooler. If so, check for blockages after doing 1, above.

3. Confirm the oil hoses from the oil tank are going to the correct spots as per the diagram above. Check to make sure connections are tight.

4. Check the vacuum hoses - all tight?
Old 03-29-2013, 12:13 PM
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Guys,

Thanks for the good hints. The diagram is really helpfull to understand potential problem.

- First, yes I have done the initial break in, where pressure was at a solid 2.5 bar at 2000 Rpm. Keep this for 10 min. Then shot the engine and let it cold for a day. Change the oil. Then start the engine when notice the low pressure at idle.
- I am almost 100 % sure chain tensioner piston were install correctly, with the hole pointing toward the cap, however will double check.
- the hoses are in correct location
- cooler line was left untouched.
- rocker arm holes and tube where clean extensively, varsol, breakckeaner, air, etc.
- vaccum hose are all tigth.
- rod bearing clearance was check using platigauge and was within spec.

Based on everyone comment i will check the pressure with a manual gauge. Then if pressure still low will look if I forgot something in the pump inlet. If problem remain, will tear the engine...

Thanks to all, help is really appreciated.

Pat
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Old 03-29-2013, 12:38 PM
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Let us know what you find!
Old 03-29-2013, 12:58 PM
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Quote:
- I am almost 100 % sure chain tensioner piston were install correctly, with the hole pointing toward the cap, however will double check.
So was I. That is, until I went in there and looked. Sure enough, I had it in there upside-down!
Old 03-29-2013, 01:04 PM
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1 bar / 1000 rpm is what I have always heard. At idle .75 bar would be pretty close to 1 bar /1000rpm.

Is that .75 when the engine is cold or after it warms up?
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Old 03-29-2013, 02:49 PM
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Every 993 engine I've ever seen idles at 3Bar and hits 5 bar almost immediately at like 2000 RPM. 1bar/1000 RPM should be the min for an early engine oil pump IMO.

I'd verify with a mechanical gauge or known good setup first. You don't want to be chasing a ghost.
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Old 03-29-2013, 06:27 PM
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Guys,

First tanks again for you help and support this is really helpfull to diagnose this problem.

I did check the oil pressure reading with a manual gauge and reading from car ( oil sender) and manual are same.
I did also look in the pump inlet: everything is clear.
Lines are also all clear.
Only the chain tensioner remain left to check, but I run out of time...family was back and I had to stop for the night.

I notice two things however, nut at the front of the engine ( flywheel) is oily and the oil color was unusual which is weird for oil with not even 1 hrs of running. ( like if foaming).

Unfortunately I did not took pictures this time.

Peppy:
The 0.75 bar is at warm temp. I got 1 bar when cold. Before the rebuild I had solid 2.5 bar at idle warm.

Green993:
You are right, in situation like this everything can be questioned, therefore my next step, is to check the chain tensioner.
Then if they are good, the next step is the tear the engine apart. Something is telling me that one if the O-ring in the case as not seated properly. Something I did not mentionned, is that the breather cap gasket was leaking after the initial startup, which after thougth, could be related to pressure in the case.

Again many thanks,

Pat
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Last edited by pat_thonon; 03-29-2013 at 07:58 PM..
Old 03-29-2013, 07:48 PM
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Guys,

I did check the chain tensionner an they were installed properly.
However did find the problem, teared oumpm seal ring:



Most likely badly seated when joining the cases half; lesson learned here. I will investigated a bit further just un case something else append. On the positive side engine did not suffer from low oil pressure, everything is good.

Pat
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Old 04-02-2013, 12:44 PM
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Well glad you found the problem. Sorry to see you had to open the case but obviously that's what was needed.

On the oil pump, i'd recommend changing out the mounting nuts to an all-metal locknut instead of the nylock type. Nylon is not too good when submerged in oil. Or you could use the locking tab plates.
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Old 04-02-2013, 01:42 PM
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OHHH Uhh where is the rest of it ?
Old 04-02-2013, 02:39 PM
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I need to trace the pieces. I kept the oil filters, most likely in there. However, i need to make sure no holes are blocked, the came tower appeared to be free of debris, but i need to triple check this.

KTL:

The mounting nut for the pump are the all metal lock nut. I personally don't like to use nylon lock when oil or heat is involve.


Pat
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Last edited by pat_thonon; 04-02-2013 at 03:43 PM.. Reason: Answer a comment
Old 04-02-2013, 03:12 PM
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The good news is No Damage , right ?
If i remember right i put some silicone grease around the pump sealing rings to hold them in place.....and prayed while I dropped the other case 1/2 on......
Old 04-02-2013, 03:19 PM
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Well, you identified the problem very quickly. It looks like you are good to go with a new seal and finding the debris. I will be doing this soon (case mating). There's got to be a better way than prayer. Maybe using a boroscope right up until the last 1/4 inch to ensure the seal?

When you closed it up do you remember how you did it. I think we can all learn from this lesson. Thank you.
Old 04-02-2013, 08:50 PM
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