Bmw e30 m20 cold start help
Moderator: martauto
Hi all I have a serious cold start problem on the e30 I have it’s a m20b20 and by the day it’s getting worse. I struggle starting the car from cold and usually have to hit the accelerator from cold and cranking it to start for I’d say 15-20 seconds only when cold. Since I’ve bought this car I’ve never seen the engine temperature on the instrument panel go more than a quarter over or even half. Was wondering could this cold start be a result of the blue engine temperature sensor or the brown one? Or anything else? All fuel lines and breathers have been replaced along with the valve timing etc.... on a warm start it starts as t shud with ease? Hope to hear from you guys soon
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Brianmoooore
- E30 Zone Team Member
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- Joined: Mon Jan 10, 2005 11:00 pm
The engine management system on the M20B20 varied from prehistoric to something recognisably similar to that on modern cars over its production life, so we need to know the age of the car.
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
That makes it the more modern incarnation of the management. It will be running on Motronic 1.3.
Correct running position on the temperature gauge for this engine is just past the 'quarter mark'.
Cold start enrichment is performed electronically on this engine by increasing the duration of the injector pulses when cold, as determined by the 'blue' coolant temperature sensor, and the engine should start on the first firing stroke of a cylinder, after the index notch on the crank pulley has passed the crank position sensor.
Three possibilities, going on the info. you have given.
1/ The ECU is receiving wrong information from the coolant sensor, and thinks the engine is already hot.
2/ At least one injector is leaking fuel into the inlet plenum when the engine is stopped, making the mixture too rich to ignite until it has evaporated and passed through the engine. There's a variation on this, where the fuel pressure regulator leaks fuel into its reference vacuum pipe, and hence into the inlet plenum.
3/ The fuel pressure in the fuel rail isn't being maintained when the engine is off, and has to be built up by the pump before the engine will start. This can be because of a simple leak, a faulty non return valve in the fuel pump, a faulty fuel pressure regulator, or leaking injectors.
1/ The blue temp. sensor is non too reliable, and it's signal passes through a seven pin round plug and socket under the inlet manifold, which also has known issues, BUT the normal effect of faults with either of these is for the car to start near normally, and then become undrivable as the engine warms up.
You can test for resistance of the sensor, with the engine stone cold, and then again at full working temperature, AT THE PLUG FOR THE ENGINE ECU.
2/ This seems the most likely cause. 2 and 3 are linked together, because a leaking injector will obviously cause the fuel pressure to drop, and to test for this you will need a cheap (£15 or so) ebay fuel pressure gauge kit, and a hose clamps, that squashes and seals rubber hoses. The gauge is connected up, using a tee piece and short piece of fuel hose, and the gauge noted after the engine is stopped, to see if the residual pressure drops off. If it is maintained, then all is well, but if it drops, then the clamp is used to seal the feed and return hose in turn, to see if that makes a difference. If not, then it must be leaking through an injector, or the FPR vacuum line.
The FPR can be checked for leaking into its vacuum hose by temporarily including a length of clear PVC hose in line with it, and watching for fuel passing along it.
Correct running position on the temperature gauge for this engine is just past the 'quarter mark'.
Cold start enrichment is performed electronically on this engine by increasing the duration of the injector pulses when cold, as determined by the 'blue' coolant temperature sensor, and the engine should start on the first firing stroke of a cylinder, after the index notch on the crank pulley has passed the crank position sensor.
Three possibilities, going on the info. you have given.
1/ The ECU is receiving wrong information from the coolant sensor, and thinks the engine is already hot.
2/ At least one injector is leaking fuel into the inlet plenum when the engine is stopped, making the mixture too rich to ignite until it has evaporated and passed through the engine. There's a variation on this, where the fuel pressure regulator leaks fuel into its reference vacuum pipe, and hence into the inlet plenum.
3/ The fuel pressure in the fuel rail isn't being maintained when the engine is off, and has to be built up by the pump before the engine will start. This can be because of a simple leak, a faulty non return valve in the fuel pump, a faulty fuel pressure regulator, or leaking injectors.
1/ The blue temp. sensor is non too reliable, and it's signal passes through a seven pin round plug and socket under the inlet manifold, which also has known issues, BUT the normal effect of faults with either of these is for the car to start near normally, and then become undrivable as the engine warms up.
You can test for resistance of the sensor, with the engine stone cold, and then again at full working temperature, AT THE PLUG FOR THE ENGINE ECU.
2/ This seems the most likely cause. 2 and 3 are linked together, because a leaking injector will obviously cause the fuel pressure to drop, and to test for this you will need a cheap (£15 or so) ebay fuel pressure gauge kit, and a hose clamps, that squashes and seals rubber hoses. The gauge is connected up, using a tee piece and short piece of fuel hose, and the gauge noted after the engine is stopped, to see if the residual pressure drops off. If it is maintained, then all is well, but if it drops, then the clamp is used to seal the feed and return hose in turn, to see if that makes a difference. If not, then it must be leaking through an injector, or the FPR vacuum line.
The FPR can be checked for leaking into its vacuum hose by temporarily including a length of clear PVC hose in line with it, and watching for fuel passing along it.
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
DO NOT EVEN THINK OF TOUCHING THE TEMP. SENSOR UNTIL YOU HAVE TESTED IT AT THE ECU!
Test first, and only then touch if tests faulty. Random part changing and generally disturbing things often introduces new faults, making the original fault almost impossible to cure.
Test first, and only then touch if tests faulty. Random part changing and generally disturbing things often introduces new faults, making the original fault almost impossible to cure.
Hi Brian I’ve been up to some investigation the blue temp sensor reads 1800-2000 ohms. At the sensor I’ve checked this at the ecu and it’s not reading this I’ve then checked from the sensor to the c191 joint and it’s dud. Only one point makes a connection the other is dead I’ve them checked the wire from the c191 joint to the ecu and once again only one point makes a connection this tells me both the c191 cable is buggered along with the loom that goes to the ecu is that correct? And seing the ohms for the sensor is only showing 1800-2000 ohms where it should significantly be 3500-4000 should I replace both the cables in the loom and the sensor too?? Including the c191 loom ?
Thank u soo much Brian for the fast responses buddy honestly your a great help hope to hear from you soon cheer
Thank u soo much Brian for the fast responses buddy honestly your a great help hope to hear from you soon cheer
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
The C191 was only fitted on post'87 M20 engines, presumably to make factory engine assembly easier.
The cheapest and most reliable way to deal with the problem is to eliminate it completely, and go back to the pre facelift arrangement, by cutting off the plug completely and soldering the wires together, insulating them with heat shrink tube. Unfortunately, the moisture is likely to have travelled back inside the wires, under the insulation, and you may have to cut back several inches to find bright copper that can be reliably soldered, so you will probably have to make two joints per wire, splicing in an appropriate length and gauge of new wire.
Stagger the joints, and bind the repaired loom up properly with the correct tape, and the repair will be visually undetectable.
The brown/white wire isn't used, so can be abandoned.
Your blue sensor's cold resistance appears to be out of spec., but don't forget it drops rapidly with increasing temperature, and your reading would be correct for just over 20 degrees. The only trustworthy way to test a blue sensor is to slowly warm the suspect one and a known good one together, comparing resistances with two meters.
I'd repair the loom first , and see what it's like then.
The cheapest and most reliable way to deal with the problem is to eliminate it completely, and go back to the pre facelift arrangement, by cutting off the plug completely and soldering the wires together, insulating them with heat shrink tube. Unfortunately, the moisture is likely to have travelled back inside the wires, under the insulation, and you may have to cut back several inches to find bright copper that can be reliably soldered, so you will probably have to make two joints per wire, splicing in an appropriate length and gauge of new wire.
Stagger the joints, and bind the repaired loom up properly with the correct tape, and the repair will be visually undetectable.
The brown/white wire isn't used, so can be abandoned.
Your blue sensor's cold resistance appears to be out of spec., but don't forget it drops rapidly with increasing temperature, and your reading would be correct for just over 20 degrees. The only trustworthy way to test a blue sensor is to slowly warm the suspect one and a known good one together, comparing resistances with two meters.
I'd repair the loom first , and see what it's like then.
Excellent buddy I’ve just done the test with the wiring and done a cold start today fired up right away beautifully so it was the wiring going to finish the wiring off properly now that’s a good job done thank u so much for the help buddy couldn’t have been done without your help thank u