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BMW Check Valve...

M

mrtosh

NAXJA Forum User
Location
Woodbury, MN
I'm having problems w/my '94 starting after it's warm and sitting for about 20mins. When it's cold it fires right up. if you let it sit for about 10 mins., it'll fire right up. 20 mins- an hour it'll crank forever, sputter a lil like it wants to start, then finally start after about 10-15 secs of cranking. Does anybody think that putting in an inline checkvalve would help. I could understand it losing pressure after about an hour and causing lil hard start, but why would it start up the next day when it's cold??? I'm pretty lost

Thanks in advance..

Sean
 
It doesn't sound like the usual pressure loss problem. But next time you're doing a hot start, try the procedure that usually works for pressure loss on cold starts. Turn key on without starting, leave on for about 5 seconds, off and immediately on again for about 5 seconds, off then start. If the problem really is from leaking down, it should start pretty quickly then.

I suppose I should add the question of whether or not you've checked your fuel filter, and also whether or not there's a problem with your evaporative emissions setup - a clogged charcoal canister, for example, can cause odd problems when things get hot. Before trying a hot start, check the gas cap. If you get a big whoosh when you crack it open, there's something wrong.

It might also be worth checking for spark when you're having the problem. Your crank position sensor could be getting balky when it's hot.
 
Had a similar problem on my 96 XJ 4.0. I would start it cold, drive it for 2 miles, go shopping for 10 minutes, it would not start unless you told it that it was flooded. I had to push the gas pedal to the floor and it started. Turned out that the mechanic that changed my T-stat put in a 160 degree and that was the problem.
 
Matthew Currie said:
It doesn't sound like the usual pressure loss problem. But next time you're doing a hot start, try the procedure that usually works for pressure loss on cold starts. Turn key on without starting, leave on for about 5 seconds, off and immediately on again for about 5 seconds, off then start. If the problem really is from leaking down, it should start pretty quickly then.

I suppose I should add the question of whether or not you've checked your fuel filter, and also whether or not there's a problem with your evaporative emissions setup - a clogged charcoal canister, for example, can cause odd problems when things get hot. Before trying a hot start, check the gas cap. If you get a big whoosh when you crack it open, there's something wrong.

It might also be worth checking for spark when you're having the problem. Your crank position sensor could be getting balky when it's hot.
Click to expand...

I've changed the fuel filter, cap, rotor, plugs, wires, coolant sensor. The guy i bought the jeep from said he replaced the CPS a while ago. My temp does constantly cycle from 175-210 back and forth. I'm wondering if that's playing with the computer throwing it off some....?? I've bled the system a couple of times now. New thermostat, water pump... I'm at a loss right now..
 
I had a bad wire going from the temp sensor, it had rubbed raw right where it leans against the firewall.I fixed it, and put an electric tape sleeve on it to prevent further abrasion. It works fine now.
 
I swapped in a new superstant thermostat and the fluctuating temp is solved. It does however, still start hard when warm. I've ordered a check valve through BMW. I wouldn't think it would be the CPS seeing as how when it does start it sputters a bit like it's not getting any fuel. But that doesn't quite explain why it starts perfect when cold...
 
mrtosh said:
I could understand it losing pressure after about an hour and causing lil hard start, but why would it start up the next day when it's cold??? I'm pretty lost

Thanks in advance..

Sean
Click to expand...
Leaky injector(s)?

tom96xj said:
I had to push the gas pedal to the floor and it started.
Click to expand...
I'm thinking that would fit your timeline. You have a Pressure gauge?
 
what would be a tell tale sign of a leaky injector? There isn't any gas in the oil... Couldn't that also be a sign of a bad check valve?
 
When my fuel pump (check valve) was going out, it was hard to start cold as well.
Another possibility would be a sensor or control out of range when the engine is at operating temp.


Here is a link to my big fuel adventure: http://www.naxja.org/forum/showthread.php?t=96729

I never did find the BMW check valve.
 
Last edited:
xjbubba said:
The FSM for my '88 4.0 says record pressure at idle, shut down engine, let set for 30 minutes and recheck pressure (engine still off). Pressure should be 19 to 39psi. Excessive drop indicates bad check valve.
Click to expand...
Problem #1?
Gotta remember it's 13 years old, there could be more than one thing going on. Follow up on the fuel diagnostic from my old thread. The 20 minutes thing has me thinking there is more to the hard start condition. Mine was a real bear first start-up of the day. Cycling the key helped; first clue to line pressure.

If there were drivability problems at temp I'd be thinking vacuum leak as well: Not the case or you would definitely mention it.
 
mrtosh said:
just checked my schrader valve and after it was sitting for about a hour. No fuel came out at all..... Soo.????
Click to expand...

So the fuel is going somewhere. Now you have to find out, if you can, whether it's going back to the tank or leaking out of an injector that hasn't closed properly.

Does it smoke when it restarts?
 
Hypoid said:
Problem #1?
Gotta remember it's 13 years old, there could be more than one thing going on. Follow up on the fuel diagnostic from my old thread. The 20 minutes thing has me thinking there is more to the hard start condition. Mine was a real bear first start-up of the day. Cycling the key helped; first clue to line pressure.

If there were drivability problems at temp I'd be thinking vacuum leak as well: Not the case or you would definitely mention it.
Click to expand...

I did however, today @ work let it run and then turned it off. Waited 30 mins and just a lil dribble of fuel came out. You'd think w/even 10-15 psi it would squirt pretty good. Nope just a lil dribble... Picking up the check valve from BMW Friday, hopefully that's the problem. Don't think it's a bad injector(no fuel in the oil, no smokey starts, or raw fuel smell), might be a bad FPR, but if it has little to no pressure after a 1/2 hour then that leads me to believe the check valve is bad... What do you guys think?
 
Matthew Currie said:
It doesn't sound like the usual pressure loss problem. But next time you're doing a hot start, try the procedure that usually works for pressure loss on cold starts. Turn key on without starting, leave on for about 5 seconds, off and immediately on again for about 5 seconds, off then start. If the problem really is from leaking down, it should start pretty quickly then.
Click to expand...
Tried this yet?

The pump on our other car went about the same way last summer; after some run time and shutting down, there wasn't enough pressure to restart. We had to wait for the pump to cool. That lasted only a few weeks before the problem became obvious. :doh:
 
When attempting to diagnose problems with engines equipped with electronic fuel injection, the FIRST thing you do is check fuel pressure. And I don't mean by estimating pressure using the schrader valve "squirt" test. You need a real pressure gauge capable of accurately measuring the pressure. The ECM assumes pressure is correct. It has no way of knowing it's not; therefore, all injector on- times/pulse widths assume the pressure is right. If it isn't, it's only speculation on what affects you may encounter.
So get a gauge and check the pressure and the pressure regulator according to the procedure specified in the FSM. A leaking diapragm in the pressure regulator can cause a rich mixture while running and a loss of pressure while sitting. A leaking regulator could cause loss of pressure while running and sitting. You need to know the actual status of the fuel supply system, and it takes a fuel pressure gauge to determine it.
 
Soo, I put in a BMW check valve and yet no results. Still takes a long time to start when warm. I'm thinking it's either the Fuel Pressure Regulator or the CPS. The only reason I'm not automatically assuming it's the CPS is because once started it acts like it's starving for fuel, then kicks right up to where it should be. If you were to shut it off, then get back to it within 10 mins, it fires right up. You would think that if the CPS was getting balky when warm, it would take the same amount of time to fire it up the second time?
 
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