RBP

I had the engine out, heads were rebuilt, cylinders cleaned and new rings were installed. When I started the engine it seems to be running very rich, was hunting and seems unstable. I did a compression test to see what I had and got 205# all around. Is this possible, anyone know what I should have. Maybe the 205# is correct considering the assy lube on the new rings and all. Anyone experience this?

I was thinking there is something wrong as people are telling me I should have say 170# PSI. If the specified compression ratio of 11.5:1 is true then say 15 x 11.5 is around 170. How can I have 205? Am I missing something here?

As far as the bad running I've double checked everything and all connections are correct. I ran my buddies Durametric OBDII scan tool to see what I can find out. It doesn't seem to want to save any running data so I have to write everything down by hand. I have no CEL or fault codes. It reported the injection time at 36.8 ms, throttle plate angle at 0. I have some other info but now have to try to determine what are good bench marks so I know what I should be read as opposed to what I am reading. I have something called a "load signal" at 4.0. Not sure what that is, maybe that's causing the injector time to be way to high.

IainM

What makes you thinks it's running rich?

205lbs is great

did you do the correct start process to set the rings?

are all the hoses on correctly and sealed?

what was the reason you rebuilt in the first place?

dint see a problem here yet

pp000830

+1
Andy

tstafford

Assuming the compression test numbers are close to the same across all the cylinders, I'd chalk that up as a red herring - and say they are great actually. At least you can stop worrying about that part.

RBP

Its running rich due to putting out black smoke, note the plugs that I took out to do the compression test. The Durametric OBDII reports injector time at idle 36.8 ms (very high) should be 2.5 to 5 ms! Not sure why its doing this. All hoses and connections are on right and tight. O2 sensors are new. The Durametric reports "load signal" at 4 not sure if that's good or bad. Throttle plate angle at idle is 0. Ignition timing seems to be bouncing 3 - 9, not sure if that's normal or not. Wasn't aware of a process for the new rings. They were installed with assy lube and seem fine.

Pulled engine to replace the clutch, flywheel and pressure plate. Thought I may as well get the heads done and replace the valve guides. Also the 2ndary air injection passages and valves were plugged so addressed that as well. Didn't like the cam drive sprocket setup so I changed that to the 964 setup, much more solid and secure.

Churchill

You can rebuild an engine but you've never heard of seating rings? Seriously? And did you really put assembly lube on the rings???

INTMD8

My thoughts/questions come from experience with other brands and not 993 specific fwiw.

I don't know what stock cranking compression is. If all components are stock, the only thing that would -increase- cranking compression by a measurable amount is advanced cam timing.

36+ ms at idle is insane and I wouldn't even think it would even run to be honest. What is key on engine off map reading, and idle maf output/map kpa,...coolant temp?

RBP

Here are the readings I got from the Durametric OBDII. Its the data when the engine is running. Unfortunately you can't download it, its gone as soon as you turn the engine off. I wrote this down when we had the engine running. There is no coolant, engine is air cooled.



Used a ring compressor and lube to slide the new rings and original piston back into the cylin

ders after cleaning everything.



Ignition Timing - Bouncing 3 - 9

Load Signal - 4.0
Voltage - 13
Cylinder Head Temperature - 110
IATS - 38
Spec Air Mass - 38
Spec Air Adaption - 0
Airr Mass - 55 - 60
Adaption Tank Vent FTA - .98
Range 1 Cylinder 1 - 3 TRA - 0
Range 1 Cylinder 4 - 6 TRA 2 - 0
Range 2 Cylinder 1 - 3 FRA - .96
Range 2 Cylinder 4- 6 FRA 2 - .96
O2 Sensing FR - .73
O2 Sensing FR 2 - .73
O2 Sensor Bank 1 Volt Before Cat - .91
O2 Sensor Bank 1 Volt After Cat - .89
O2 Sensor Bank 2 Volt Before Cat - ..91
O2 Sensor Bank 2 Volt Before Cat - .89
Hot Film MAF - 1.5
Ambient Pressure - 960 HPA
Injection Time - 36.8 ms
Throttle Plate Angle - 0

Churchill

I believe you, but that certainly isn't a picture of that procedure. That's three pistons hanging off the engine with no cylinders.

Seating rings is the same in every internal combustion engine, there's nothing about it specific to Porsche. I would do some googling. I hope it's possible on your engine even though you used assembly lube, which is the exact opposite (you either install the rings dry or with a very slight film of low-viscosity oil, like 20 weight). You want the rings and cylinder walls to wear into each other, which is how they "seat."

RBP

The picture is just my block, showing that I didn't split the case. I just cleaned the pistons off, made sure everything was extremely clean then installed the new rings on the existing pistons and then installed the cylinders back on the cylinders from which they came.

Catorce

First of all, STOP with the scan tool. Yes, I know 993s can use one, but the engine in question began life in 1965. There is something ELSE wrong with it, and no computer will help you diagnose it.

You glossed over a lot of details the assembly, and to be perfectly frank, using assembly lube on piston rings tells me that you aren't quite up to speed on how a Mezger motor gets built.

Here are the issues you need to make certain of:

1. Distributor reinstalled properly, not 180 degrees off.
2. Cam timing set per whatever spec your cams are. This in and of itself requires a bunch of special tools, do you own these? Tell us more about what you did here.
3. Both cams installed in proper phases. Yes, you can have one cam installed 180 degrees out and the motor will still run (badly) ask me how I know.
4. And this is a distant 4th....all intake manifolds and plenum installed without air leaks.

You 100% have a hardware issue here so you can kill the durametric for now. This is not a 2019 car and you will not be able to fix it with a laptop.

Steve Weiner-Rennsport Systems

Make sure the cylinder head temp sensor is connected and working properly.

JasonAndreas

Durametric is calculating the wrong display value for the injection time, or you misplaced a decimal point? It is more than likely 3.68ms and not 36.8ms. Your "spec air mass" (what it thinks air intake should be at idle) and "air mass" (what it measures at idle) should be the same and will eventually get there. Your TRA values (fuel correction @ idle) is 0 but you probably haven't run the engine long enough for the ECU to start paying attention to the O2 sensors? What RPM was the above snapshot taken at? 4% load during warmup is not unusual and it will eventually drop down to 1% @ idle. A CHT reading of 110C means you are only in part #2 of the 3 part warmup phase. And that will dump extra fuel into the intake. A snapshot of your o2 sensor values is meaningless. Are the readings pegged to one side or bouncing back and forth? After running for about 6 minutes it will run a plausibility test that will tell you if there is too much fuel going into the intake.

A distributor that is 180 degrees out of phase will usually backfire and pop the intake manifold so it is unlikely to be that. But timing the cams wrong would do it. How long did you run the engine? Are you certain the black smoke is not from oil? You did just replace the rings.

RBP

Distributor is in correct, #1 at TDC compression stroke and rotor lined up with notch on housing.

I set the cams using a Z block, solid rocker/lifter and gauge as follows.
Setup valve clearance at 1mm
Set Cyl #1 to TDC
Cyl #1 Intake valve should be set a 1.26mm lift
Same process for other side on cylinder 4.

Cylinder head temp is reading right, used an ohm meter to verify.

The Vario Ram intake was reinstalled with all new boots and fittings, everything is tight/snug. Injectors were sent out serviced, cleaned and tested with new O rings in place.