93 850 the dreaded warm start problems, cranks but no start Topic is solved

[misha]

...I purchased a working coil from a salvaged ( due to accident ) 1998 S70 on ebay for a very good price. I did match the part number with compatibility and from what I can find, it is compatible with a 1993 850. I will put it in as soon as it arrives and report back my findings.

Thank you again!

According to jreed's specs...your coil is withing specs.

[misha]

...I checked both ends of the positive cable on the battery and the starter and they are both tight and corrosion free.

How did you checked them...visually?

They all look fine visually,the problem is that they are not usable(electrically).

The only way to check them is a voltage drop test on both...positive and negative side...BUT only after about 30min of driving and WITHOUT turning the engine off.

Alternator charging output should be checked also on both...battery terminals and alternator directly.Voltage differences should be within 0.2v.

[93ForMe]

According to jreed's specs...your coil is withing specs.

Hmmmm.
According to jreed:

For pre-1994 B5252S engines, the primary resistance is "not specified" and the secondary should be between 6000 and 7000 Ohms.

I have a 1993 850, so if I am reading this correctly 7000 Ohms should be the max resistance and my coil was reading 8900 Ohms. This 8900 Ohms reading would be in spec for any 850 but my 93. Please let me know if you see a mistake here.

[93ForMe]

...I checked both ends of the positive cable on the battery and the starter and they are both tight and corrosion free.

How did you checked them...visually?

They all look fine visually,the problem is that they are not usable(electrically).

The only way to check them is a voltage drop test on both...positive and negative side...BUT only after about 30min of driving and WITHOUT turning the engine off.

Alternator charging output should be checked also on both...battery terminals and alternator directly.Voltage differences should be within 0.2v.

I am thinking that it is not a starter problem because it starts just fine any time except after driving it for 2-4 miles for the first time I that drive it every day. The engine starts lurching and runs a little rough during this time. Turning the car off at this point will make it crank and not start. If I wait 25 minutes it starts just fine the first try and then it starts just fine the rest of the day.
If I tap the gas pedal during this rough period I can get it to stall out. The engine chugs and rumbles, then quits, and it will then crank, but not start.

I could be wrong though! I am pretty new to all of this.

[misha]

Is your 850 10v or 20v car?
10v cars were not imported in U.S.
B5252 is 10v car.
Is CEL on?
Read the codes from A2 and A6.
'93 non turbo have two separate ecu(s) for engine(A2) and ignition(A6).
You have built-in diagnostic ports under the hood on ecu box.

[93ForMe]

Is your 850 10v or 20v car?
10v cars were not imported in U.S.
B5252 is 10v car.

My engine is a B5254S. You are correct, that makes it a 20V, if I am looking it up correctly.

Is CEL on?

The CEL is not currently on. It does work, it turned on when I disconnected my MAF

Read the codes from A2 and A6.

Both A2 and A6 are reading 1-1-1

[misha]

Then your coil is ok.
B5254S also have 20v designation on valve/spark plug cover...while 10v cars have DOHC instead of 20v.

[93ForMe]

Then your coil is ok.
B5254S also have 20v designation on valve/spark plug cover...while 10v cars have DOHC instead of 20v.

Thanks for that! I am learning new things.

If it is not the coil, do you have any idea what else it could be? The ECU? I have tried almost everything else that I can think of.

[misha]

Perform a voltage drop test in order to see are main b+ cable and ground ok.

TDC sensor(on flywheel) should also be checked.
ECT sensor's connector from ECT side and wiring loom side should be checked for corrosion.

[93ForMe]

Perform a voltage drop test in order to see are main b+ cable and ground ok.

I think that I just complicated things a little bit on my end. I have not done a voltage drop test before, so I watched a few videos on how to do one properly before getting started. I also impulsively decided to quickly pull the two ECMs to check for corrosion. I found none on the units, so I put them back in. I then went to start the car to let it heat up properly for the drop down test. For the first time it was hard to start on the first try. It took two cranks and rumbled to a start.

I let it run about ten minutes and it started running quite rough, and then it stalled out and would not restart. I then decided to check the coil again, since the car had warmed up longer than when I had taken the measurements this morning. This time the resistance was 9,300 Ohms. I don't think that the engine was up to full operating temp at this point.

Could re-seating the ECM cause the car to act differently then it did before?

So it looks like the Coil is a problem, but it might not be the only one.

Or perhaps the ECM is a red herring and it is just the coil getting worse.

ECT sensor's connector from ECT side and wiring loom side should be checked for corrosion.

I think that I will wait until the replacement Coil arrives and install it and see what happens in order to better attempt to isolate my issues. I will then do the voltage drop test and inspect the wiring harness/ECM side of the ECT connections.

I haven't been doing car repairs for very long, so I get nervous opening up too many potential problems at once.

Thank you for all of your help! I will get back to it as soon as the part arrives.