The Stumbling M20 Engine

[Quinthirty]

Glad to hear you sorted out one of your problems. Your other problem could be the cylinder head. Does you car smoke/steam out of the exhaust? It is common for bmw heads to crack from overheating. When you turn the car off, the water pressure will cause some water to enter the piston chamber. This could be the reason for a tough start. I had this issue, but mine was because of a bad gasket.
Goodluck!

No smoke, no overheating, no milkshake either in the water...and this baby sits in traffic much like the 405 daily. I think this a rebuild scenario you're talking about but I don't think this engine is close to getting there yet. Thanks.

[Quinthirty]

Car is idling well now. But I'm still stoked by the hard start sometimes. It took me three clicks yesterday after stopping for an hour. This morning's cold start also took 3 attempts.

I almost run the tank to empty last week because of bad traffic, and I think that my fuel pump sucked the dirt from the bottom of the tank. Anyone knows how to clean the pumps? I don't want to take it to a shop.

[jlevie]

Thanks for the tips, gents. I'll clean the CPS.

I did the injectors-and-chip combo. I have a spare 173 stock ECU though, and I'll probably replace it now that Jim mentioned that it can run with the stock DME. It'll save me some gas money too, as the chip requires higher octane fuel or it knocks like crazy.

I said that the DME can adjust to those injectors, not that it was a good idea. Nor is there any performance advantage to larger injectors unless some serious work has been done on engine internals to significantly increase mass flow through the engine (or FI). The stock injectors (if clean and working properly) are more than the engine needs as is.

I've also replaced the vacuum hose from FPR to manifold. That is one of the 1st ones I replaced when I got the car as I noticed that the hose was quite old. All other hoses i.e. to ICV, valve cover are all good. The only ones that are left are the "complicated hoses" on the throttle body, so if the rough idle doesn't go away after I replace the O2 sensor, that will have to be replaced too.

All hoses on an E30 (including the cooling system) should have been replaced twice by now (every 10yr/100k), but the odds are that none have been replaced. Best practice is to just replace all or the hoses. Then have a smoke test run to check for leaks elsewhere.

I'm not sure if the brake pressure is also related as I notice sometimes when I'm in a stop and my foot is resting on the brakes, the pedal goes all the way down. But when I step on it again, the brake pressure is back. I was told that to test which one has a leak, turn off the engine, and pump the brakes. If the pressure holds, its the hydro vacuum, or if it releases pressure, its the master cylinder. I'm not sure whether that's a good diagnostic test though.

The pedal sinking when you hold pressure on it is either a leak or a bad master cylinder. Get the car up in the air and check each caliper and all lines for leaks. If none are found, replace the master cylinder. When replacing the master cylinder, use a a bit of rag on a wire to check the booster for brake fluid that may have leaked from the master cylinder. If there is brake fluid in the booster it will need to be replaced also. Brake fluid will destroy the diaphragm in the booster pretty quickly.

[603Racing]

Hard cold start still... hmmm. Maybe the "check valve" isn't functioning. Assuming my memory is correct in that the fuel pump has a built in check valve or check valve type function to keep the fuel pressure on the rail when the car is off.

17lb injectors are close enough to the stock injectors that the DME can learn how much less fuel to inject for proper operation if the O2 sensor is good and there are no other engine management problems. That won't work with larger injectors because the available fuel trim is limited and the DME can't fully correct for the increased flow.

Noted... perhaps in my experiences I didn't give the DME enough time.

M20/30 engines aren't unique in the this respect. Any engine with electronic fuel injection is extremely sensitive to unmetered air. And modern engines have lots of places to leak.

True, and I wasn't trying to imply they are bad or worse than any other motor. I was just referring to the motors most often associated with vacuum leaks on R3V. In fact the '94 4 Runner I had had the worst air leak engine I've ever dealt with, lol. That thing seemed like it had enough vacuum lines to stretch from New York to LA!

[e30construction]

i also plan to clean the cps..do i disconnect the plug before taking it off or leave it on?

[jlevie]

A bad check valve in the fuel pump can mean that it will require an extra few turns to achieve normal pressure in the rail. But usually by the time that happens the fuel pump(s) are pretty worn out, extending the time to pressurize the rail. If the fuel pump(s) are good two to three turns of the engine are all it takes to get full rail pressure from a dry condition.

In most cases, cleaning the CPS is meaningless. The problem will be a loss of magnetism in the core of the CPS or a problem in the CPS cable. Just replace it with a new BMW part.

[e30construction]

i just wanted to take it out and clean it for no reason even tho it was pretty gunked up..i dont have any of the above problems i just wanted to know how hehe

[Quinthirty]

I said that the DME can adjust to those injectors, not that it was a good idea. Nor is there any performance advantage to larger injectors unless some serious work has been done on engine internals to significantly increase mass flow through the engine (or FI). The stock injectors (if clean and working properly) are more than the engine needs as is.

Noted, Jim. I still have the stock ones with me. I'm still looking for a place here where they can do ultrasonic and flow testing, and someday, I'll probably put them back.

All hoses on an E30 (including the cooling system) should have been replaced twice by now (every 10yr/100k), but the odds are that none have been replaced. Best practice is to just replace all or the hoses. Then have a smoke test run to check for leaks elsewhere.

Yes, the hoses in the cooling system are new. It was done by PO two years back, and she was a garage queen before I bought her.

The pedal sinking when you hold pressure on it is either a leak or a bad master cylinder. Get the car up in the air and check each caliper and all lines for leaks. If none are found, replace the master cylinder. When replacing the master cylinder, use a a bit of rag on a wire to check the booster for brake fluid that may have leaked from the master cylinder. If there is brake fluid in the booster it will need to be replaced also. Brake fluid will destroy the diaphragm in the booster pretty quickly.

I don't have any leaks on the lines nor the master cylinder, although I can feel that my brakes are a little weaker upfront compared to the back. So I might need to replace the master. I will check on the brake booster when I open the master cylinder.

Is it also possible that there is air escaping from the brake booster system and / or vacuum lines? Brake booster and master cylinder are dry. The brake fluid reservoir is surprisingly full, and the fluid is clear with no dust or dirt inside.

Thanks again, Jim.

[Quinthirty]

Hard cold start still... hmmm. Maybe the "check valve" isn't functioning. Assuming my memory is correct in that the fuel pump has a built in check valve or check valve type function to keep the fuel pressure on the rail when the car is off.

None of this hard start anymore for the past two days...but let's see.

[jlevie]

Noted, Jim. I still have the stock ones with me. I'm still looking for a place here where they can do ultrasonic and flow testing, and someday, I'll probably put them back.

I use RC Engineering for injector work.

Yes, the hoses in the cooling system are new. It was done by PO two years back, and she was a garage queen before I bought her.

That is good but what about the other parts in the cooling system?

I don't have any leaks on the lines nor the master cylinder, although I can feel that my brakes are a little weaker upfront compared to the back. So I might need to replace the master. I will check on the brake booster when I open the master cylinder.

No visible leaks doesn't mean that the master cylinder isn't leaking internally or into the booster.

Is it also possible that there is air escaping from the brake booster system and / or vacuum lines? Brake booster and master cylinder are dry. The brake fluid reservoir is surprisingly full, and the fluid is clear with no dust or dirt inside.

A vacuum leak in or to the booster results in a hard pedal. Not one that sinks.

[Quinthirty]

The water pump and seals were replaced at the same time as the timing belt and hoses 2 years back. I had the system flushed when I first got the car. I went to a shop where he had a pressure radiator wash that went through the whole system. I could see how dirty the water was in the tank that was initially filled with somekind of flushing detergent. We also took out the thermostat and cleaned it of residual gooey rust.

I still refill the system w/ distilled water and coolant though I don't know where the leak source(s) are as there are no visible leaks. On a very hot day, I could hear the water boiling in the reservoir though, so I don't know if that spills out the reservoir as overfill.

I'll check on the booster and master cylinder soon as I'm replacing the rotors.

Its also good to know that the brake system does not sound like it has a vacuum leak.

As always, thanks Jim.

[jlevie]

If the car is experiencing a loss of coolant and a pressure check does not find a leak, the coolant loss will be from the cooling system's pressure causing the cap to lift and dump coolant out of the overflow tube. That can be from a bad cap, but more often it will will be from a small head gasket leak that is pumping air into the cooling system. The venting of coolant may only occur when the car is at speed (and the engine at higher rpm) and will leave no evidence of where the coolant went.

[dnguyen1963]

The water pump and seals were replaced at the same time as the timing belt and hoses 2 years back. I had the system flushed when I first got the car. I went to a shop where he had a pressure radiator wash that went through the whole system. I could see how dirty the water was in the tank that was initially filled with somekind of flushing detergent. We also took out the thermostat and cleaned it of residual gooey rust.

I still refill the system w/ distilled water and coolant though I don't know where the leak source(s) are as there are no visible leaks. On a very hot day, I could hear the water boiling in the reservoir though, so I don't know if that spills out the reservoir as overfill.

I'll check on the booster and master cylinder soon as I'm replacing the rotors.

Its also good to know that the brake system does not sound like it has a vacuum leak.

As always, thanks Jim.

Not quite clear here...you said you have water/coolant in your car, but then "water boils" inside the reservoir on a very hot day. If you have 50:50 mix then it would have to be very very hot for it to boil. If you used 50:50 mix and you hear boiling sound then I suspect that air is being pumped into the coolant system (bad HG or warped head).

[Quinthirty]

Not quite clear here...you said you have water/coolant in your car, but then "water boils" inside the reservoir on a very hot day. If you have 50:50 mix then it would have to be very very hot for it to boil. If you used 50:50 mix and you hear boiling sound then I suspect that air is being pumped into the coolant system (bad HG or warped head).

Its not at 50:50 coolant-to-water ratio yet (yes, I didn't drain it) and maybe that's why it boils over. It used to be pure water and I've slowly introduced the coolant as its getting warmer. I drive in the tropical side of the world where the daily temp is in the 90s-100s, and the car's driving conditions are heavy traffic a la LA's 405 w/ A/C always on. Temp gauge doesn't go over 1/2. I'm unsure about the bad HG or a cracked head as there are no leaks or oil streaks in the water / coolant.

[Quinthirty]

If the car is experiencing a loss of coolant and a pressure check does not find a leak, the coolant loss will be from the cooling system's pressure causing the cap to lift and dump coolant out of the overflow tube. That can be from a bad cap, but more often it will will be from a small head gasket leak that is pumping air into the cooling system. The venting of coolant may only occur when the car is at speed (and the engine at higher rpm) and will leave no evidence of where the coolant went.

I'll have the system pressure checked then. I hope its just a cap issue. I've been wanting to replace the "re-used head bolts" the PO did anyway, so an HG leak will give me reason to remove the head, even rebuild it if necessary. I just hope that the head doesn't have a huge warp.