87 325e power loss

[Thunderzol]

Hoping someone has a pointer based on my issues.
Car has most ancillary components replaced in the engine (gaskets, sensors, TPS, hoses, seals, water pump, belts, injectors, plugs, fluids). Has been slowly losing coolant but the oil is clean and free of coolant. Most hoses seem to be overpressurized and show coolant seepage (despite tight clamps).
Head gasket is believed to be weak on its last leg but not blown.
Valve cover gasket is new BMW brand but leaks a bit oil even with proper torquing. Not detectable with vacuum test.
Idle is around 900 but not very stable. ( it’s been that way)
Fuel consumption is good at 28 mpg.
No smoke from tail pipe and no vacuum leak based on a smoke test.
Prior to this last weekend car ran fine but on the way home lost a spark plug. Immediately pulled over and plugged it back (mangled) and now replaced with new.
Now the car runs smooth but it accelerates poor and tops out at 80mph @3000 rpm.
What could be my problem?
Any help appreciated.

[tomstin]

Please define "lost a spark plug"? Blew out? Fouled with oil?

I would start with a compression test
.
What do the spark plugs look like?

How about the Mass Air Flow (MAF) sensor. You can check that with a multi meter.

O2 sensor could be sending false readings to the ECU.

I have also seen a blocked exhaust pipe restrict things to the point where the car couldn't accelerate.

[Thunderzol]

The plug just blew out (probably not torqued properly).
I’m not great with low voltage not sure how to check MAF.
o2 sensor is new, so that could be part of the issue - I’ll check.
exhaust is making a funny sound at certain rpm, so that might be the problem too.
Thanks for all the tips!

[MrBurgundy]

It could be many things..

Start with the basics; check your compression, then do some fuel pressure tests and check the ignition system.

[Thunderzol]

I will check compression. And report back. Thanks for both of the comments!

[Thunderzol]

Compression results: -165, 2-165, 3-160, 4-160, 5-168, 6-170.
When I buttoned it up, now the engine misfires where as it was smooth before the compression test :( I tightened all spark plugs, checked cables, and plugged in the fuel relay. This is the case of “from bad to worse”. Should I replace the ignition cables next? (Distributor rotor new, fuel pump and pressure regulator new, injectors refurbished)
Can I rent a fuel pressure test kit at Autozone?

[tomstin]

First, I would verify all your spark plug wires are going to the correct plug. And it's hard to check your own work as you tend to overlook things (as I have many times). If all that checks out, spark plug wires are a good preventive measure. But, if you have a pair of insulated pliers, pull one plug wire at a time and see if its one cylinder that is giving you trouble.

The compression test looks good.

How were the spark plugs? Gaps correct? All similar color and condition?

I hate throwing parts at it, but maybe the coil is flaky?

Verify the engine grounds are good, clean and tight. One on the valve cover and one under the alternator that goes from the frame to the oil pan. That one tends to corrode.

Once all this is verified AGAIN, call your local parts stores and see who can rent you a fuel pressure gauge.

Sorry, no easy, quick answer.

[Thunderzol]

tomstin thanks for all the input. Sure enough I had the ignition cable switched on cyl 5&6. :)) as for the power loss, it seems ok but I’ll report back in a 100+ miles. Plugs seemed good color and consistent but many were barely hand tight. Gap/color was good. Oil around the threads.
ground straps are new. I may replace the ignition cables and coil next. And will follow up with the fuel pressure test.
thanks again!!

[Thunderzol]

Fuel pressure test completed with mixed results:
According to Bentley the system pressure should be around
36psi with the engine off + fuel pump running (jumped fuel pump relay). CHECK!
And should be 33psi-39psi with engine running - FAIL! I am getting 28psi instead. When I pinch the fuel return line near the regulator the pressure goes up as it should. When I disconnect the vacuum line from the regulator, the pressure spikes up to 36-37psi, which should be the normal pressure (not when disconnected).
The system pressure holds pretty steady several minutes after I shut everything off.

In short, the running pressure is low but goes to normal range when the regulator vacuum line is disconnected. Can my regulator be at fault? Or should I look elsewhere?

Thank you in advance!!