Hello,
I have an 88 BMW 735i with the m30 engine and it runs perfectly, but lately I have been having some issues starting it. When the engine is cold, if I try to start it, it seems I have to turn the key twice before it finally catches and runs (turn ignition on, wait a few seconds then crank engine over, turn off and repeat). When I first turn the key the engine will spin quite a few times and sometimes the engine sounds like it was going to start but then doesn't and continues turning over, then I have to turn the key off then back on again and crank the engine over a few more times and it will finally start, it will rev up and down for a few seconds then stabilize at 750rpm and it runs just fine after. If the engine is still warm when I try to start it it starts up right away.
Less than a year ago I could turn the ignition on, let it sit for a few seconds then crank the engine and it would fire up immediately. I haven't noticed any change in how the engine runs once it starts, it idles perfectly and drives just fine, there are also no engine codes showing up either. The only thing I have changed is a few months back I added a one way check valve as I thought the one attached to the fuel pump was going since I had to let it sit with the ignition on a few seconds before starting it for it to start right away, but I'm not sure if that would be related to this issue. My battery is good and I also check the coolant temp sensor and its resistance values are within spec.
If anyone has any ideas as to what the issue could be or what I should check let me know as I'm not really sure where to start, especially because it runs fine once it starts up.
Thanks,
Timothy
Could be many causes, start to check:
Spark plugs, plug wires, distributor+ rotor, ignition coil - Clean and inspect. Especially the center pin in the distributor cap often breaks when the distributor is old
crankshaft position sensor must be 540 ohm +/- 10%
Using digital multimeter, check resistance between terminals 1 and 2 in crankshaft position/rpm sensor connector.
Crankshaft Position/rpm Sensor Specifications • Coil resistance (approx.) @ 20°C . . . . . . 540 ± 10% Ω • Air gap (sensor distance from toothed wheel) . . . . . . . 1.0 ± 0.3 mm (0.04 ± 0.01 in.)
https://wiki.bentleypublishers.com/d...=1306522675840
When did you last time change the fuel filter?
Vacuum hose to fuel pressure regulator – might be cracked/worn http://www.nmia.com/~dgnrg/hose_map.jpg
Rubber hose between Airflow Meter and throttle – cracked?
Air filter – replace if dirty, check seals
Distributor cap – if eroded and worn - changed to new one
Check fuel pressure - Replace the Fuel Pressure Regulator. Might need to replace Fuel Pump and fuel filter
Check and Adjust valves - throttle valves, PCV valve behind intake runner, Idle Control Valve (ICV)
ICV Idle Control Valve. Remove and clean it with brake parts cleaner. This regulates the air coming in to your intake manifold when the throttle body is closed and it tends to get dirty, sticky and the motor inside could not turn the valve properly
Idle control valve sometime sticks open – causes issues when in Idle
Throttle Body - Clean it out
Check all Vacuum lines.
Check throttle position switch on the throttle body.
Check for intake manifold gasket leak
Last edited by shogun; 10-31-2018 at 05:23 AM.
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Mine did this. It was the crank position sensor. Hard starting and uneven idle. I'd check the resistance for the sensor. It's fairly simple. You just unplug it from the harness at the front of the engine and poke the plug at terminals 1 and 2 with a multimeter. There are only 3 terminals if I recall properly, so you'll find it. Proper resistance is 540 ohms.
Also, if I'm right and you have to change the CPS, make sure you loop the wire behind the coolant hoses. Otherwise the pulley will wear it down, and the symptoms will re-appear.
Last edited by nm735; 10-31-2018 at 12:00 PM.
I checked the crankshaft position sensor and it measure 494ohms at 11 Celsius which should be within the 10% tolerance. Spark Plugs, and airfilter were new this year, fuel filter was replaced last year. The vacuum line going to the fuel pressure regulator looked ok but I could only see what was above the intake, I did notice that the fuel line that goes to the regulator was cracked so I replaced it, will find out tomorrow if it helped or not.
Will also check the other items you listed there when I get a chance to, thanks for the help.
Here is a pic from Jeff showing the vacuum connections under the intake of the M30 https://www.bimmerforums.com/forum/s...ntake+manifold
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As you are having to crank twice - and are then successful, it still sounds like you have reduced fuel-rail pressure on a cold-start. You fitted a one-way valve near the pump so that should take care of that end, however it is possible that the new one-way valve is not perfect! At the other end you have the FPR which acts like a one-way valve at pressures below 3 Bar.
The best move forward is to actually check the fuel-rail pressure using a cheap gauge and a 'T' piece - this can be measured anywhere between the FPR and your new one-way valve. What you should see is a quick drop from 3 Bar to 2.5 Bar when the engine is stopped. The pressure should remain at 2.5 Bar for weeks - if it drops then there is your problem!
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Will definitely check the fuel pressure when I get the chance to, as that is one thing I haven't checked as well as the vacuum lines since I doubt they have been replaced anytime recently.
It's been raining for days now, so haven't had much time to look at it since I have to work on it outside, will update on what I discover when I look at it.
Still haven't had a chance to check the fuel pressure, as I don't have the tool yet. But I have noticed that when the vehicle has sat for a while (few hours or overnight) if I try and crank the engine immediately after turning the ignition it almost tries to run but stutters, whereas if I let it sit for a few seconds then try starting it cranks forever before starting and you can smell gas shortly after it starts. Because of this I'm wondering if it might one of the injectors leaking does this sound at all like a possibility given the symptoms?
Also, is the best way to test for a leaking injector, besides a fuel pressure test, removing the spark plugs after it has sat for awhile and smell for gas in the cylinders?
Just thinking in backyard hack mechanics out loud:
-1- If you are wondering if you have a real leaking injector pull the fuel rail, extend the hoses and run the pump for a couple of seconds. If you have a really leaky one it will get wet.
-2- If its just one bad injector pull them one by one until the fuel smell goes.
-3- A rough check for the fuel pressure regulators is to unplug the fuel pressure regulator vacuum hose. Without the vacuum at idle I think it should run richer and you should notice a change in running and if fuel comes from the vacuum connection on the regulator, it's definitely shot
Note: when you pull the rail, you most probably have to replace the o-rings at the bottom + top of the fuel injectors, as they become hard and break.
O-ring 7,52 x 3,53 mm 13641730767 http://www.realoem.com/bmw/enUS/show...diagId=13_1378 available online, no need to buy from BMW
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Try pulling the plugs. I ended up pulling apart half my engine, and when I got it back together there was a misfire at high RPM. I tried everything, and while I was checking the compression I realized there was a build up on cylinder #2. A set of Gen III Ford injectors from an old Explorer cleared it right up.
I finally bought myself a pressure tester, and I measured 42psi while running. It appears to drop quickly though after being shutoff, it dropped to 38 once ignition was off and in about 30 min was below 30psi. Will check in the morning to see what it's at, but it would appear to me that its not holding as much pressure as it should.
42 psi = 2.89 bar. The operating system for the M30 is
Nominal data: The M30 fuel pump is originally Bosch, operating pressure is 3 bar, conveying capcity at 12 V 1.9 liter/minute, conveying capacity against counterpressure 875 ccm/30 seconds, Power consumption is 5A
Usually the fuel pump makes much more than 3 bar and the fuel pressure regulator controls the operating pressure, sends the excess fuel back to the tank. Read this about fuel pressure testing the M30 and also pressure in idle https://www.bimmerforums.com/forum/s...e-test-results
Ever changed the fuel filter?
So either the fuel pump or the fuel filter is the problem, I assume
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I replaced the fuel filter about the middle of last year, but it was just a cheaper one and I have no clue when the one I replaced was last changed so it maybe time to replace it again if there was lots of debris in the tank.
I checked the pressure this morning and it was down to 0 PSI after sitting overnight, I did install a one way fuel check valve a few months ago, so unless its defective it makes me think it would be either an issue with the FPR or an injector.
Also, when I disconnect the vacuum line from the FPR while the engine is running the fuel pressure does climb to 47 PSI. If the fuel pressure that I'm getting is still too low, if its not the fuel filter causing it, could it be possible that the fuel check valve I installed is restricting the flow?
I do not know what kind of check valve you installed, usually there is a spec. for the fuel check valve in throughput liters/minute or so. But in General they should all work when the diameter of the connector fits. And the check valve has outside an arrow which shows the flow direction, it must point towards the engine bay.
in brief:
within 20 - 30 minutes the pressure drop should be max. 0,5 Bar
With a pressure gauge, you can quickly find the cause:
1. Mount the pressure gauge in the supply line in front of the injection rail
2. Start the engine and switch it off after a few seconds.
3. Bend the fuel hose or compress it so that it is tight.
4. Read and note the pressure.
5. Wait 20 - 30 minutes
If the pressure has dropped by more than 0.5 bar, the pressure regulator is broken.
If the pressure remains stable, it is probably the check valve in the pump, or the pressure is leaking somewhere.
In similar way you can also check the fuel pump check valve, start the engine for a moment, switch off, bend the fuel hose between tank and engine bay or compress it so that it is tight and no return flow to the tank can happen. In case the pressure still goes down quickly, the problem is in the engine bay and not the check valve of the fuel tank.
You can do other tests like closing the fuel pressure return line, if the pressure is then o.k., it might be the fuel pressure regulator. So with each test you can eliminate one by one. check valve, fuel pressure regulator, fuel injectors.
So basically make 3 tests: start engine that there is fuel pressure, turn off engine, use a fuel line clamp hose, and close the line back to the tank. Check after 30 minutes. Next test, clamp the fuel return line after the FPR, wait, test, then to fuel injectors, test and see.
Last edited by shogun; 12-08-2018 at 11:05 PM.
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Thanks, again for the advice, will try this out next time I get a chance, hopefully within the next couple days if weather cooperates.
I tried what you had suggested and figured out it was likely an injector that was leaking, and this was confirmed when I tore the intake apart to look at the injectors, and the first injector, nearest front of engine was leaking.
Also, figured out part of what caused my hard starting issue... it was my spark plugs. Took them out and discovered they were all black with carbon, I should have checked them first but didn't since I only had 10,000km on them and my last set that I replaced before these were normal looking after more than that. After installing clean spark plugs, it fired right up even with 0 residual pressure left in the lines.
Sadly that sounds like I have another problem with something causing it to run rich... Looking on the internet it sounds like it could be either the AFM or 02 Sensor causing that?
Anyways, time to look for new injectors, any recommendations as to what works best, I read that a lot of people are using 19# injectors from a mustang?
you could sent the injectors to a service for rebuild, probably one in your area, google shows me this one, probably you know a shop in your area http://fuelinjectorprecision.com/fue...-cleaning.html
or check the internet for a set of refurbished ones.
Before you throw more parts in, I would try to find a shop which can read out the codes, the code reader will tell you what is wrong. Or get a code reader and DIY.
O2 sensor you can also test DIY: oxy sensor testing at the DME/MOTRONIC in E-box http://www.bimmerboard.com/forums/posts/622383/
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I use 19ib injectors from an Explorer. I think this was the proper part number: 0-280-155-710
These were used in a variety of applications, most of which are readily available in North American junkyards. They work well enough, It starts consistently and I have no errors on the dashboard. These are the ones to use if you want to save money.
Pulled the injectors and fuel rail and reconnected them outside the engine and when pressurized it appears that all but one or two leak to some extent so it seems my best bet is to replace them.
I'm thinking that the reason I didn't notice the leaking injectors before was because fuel check valve on the pump wasn't working allowing the fuel to go back to the tank before it would leak through the injectors, and now with the inline check valve installed I notice the injector leak.
On Ebay they offer them reman for less than $20/piece, search for Bosch 0280155700 Central Port Fuel Injector
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So I've just had a thought. On my engine, I had one leaking fuel injector. It was missing a metal point at the tip of the injector that the others had. Are your leaking injectors also missing this metal point?
My injectors were leaking right at the metal tips, not dripping, but enough that I could see the fuel bubbling.
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I ended up buying refurbished injectors off ebay and installed them two days ago. Haven't driven it too much yet so it's hard to be sure in the long term, but it appears to be running alot better now and also starts without issue, both hot and cold starts. Also seems to hold fuel pressure alot better/longer now.
Thanks again to everyone for the help with this issue.
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