P0410 cause hard cold start? Topic is solved

shegarty · Post by **shegarty** » 23 Jan 2019, 18:28

Hi all, I have been chasing a hard cold start issue for quite some time now. At first it appeared to be related to low fuel pressure and a possible leakdown issue. After ruling out leaking injectors (leak test under pressure) and replacing the fuel pump I also replaced the fuel pressure regulator. This appeared to help the issue with it only reoccurring when the temps were really low (below -15ºC).

Recently though the hard cold start issue has reappeared and now seems to be independent of fuel pressure leakdown over time (that issue should have been solved with the new fuel pump if it was the integrated check valve). The cold start consists of extended cranking time (5-10 secs) with a stutter start and what sounds/feels like misfires. Today the temps were warmer (+2ºC) and the car had not been started in two days, it cranked for about 5 secs and then ran very rough with a definite misfire (flashing lamba light) especially under load. This continued for about 10 mins of run time and then cleared up. I am now thinking that I am chasing an electrical issue as it was raining and misty today.

However, I am also wondering if the P0410 (SAS) code that it has been throwing could have any impact on start up or the rough running issue. I have noticed more recently that the headlights and interior lights will dim repeatedly (6-8 times) after cold starting like there is some electrical load being activated and the the CEL will come on and will show the P0410 code. This has been happening on almost every cold start now. My understanding is that this is part of the emissions system but could it be causing an air/fuel issue on startup?

I have some time and a garage available to me tomorrow and I plan on checking cap/wires/plugs and replacing as necessary. I have a spare coil as well and someone to help me test for a good spark. I'll also go over vacuum lines and the wiring for the injectors as I know from experience that these can get brittle over time. BTW the battery is new also. Any thoughts, ideas???

WhatAmIDoing · Post by **WhatAmIDoing** » 23 Jan 2019, 21:57

P0410 Should not cause starting issues, but you can try unplugging the air pump. It's the big gray connector in front of the battery tray. I would have your "new" battery tested, as well as the alternator just to make sure nothing fowl is there. Use a mutimeter to check voltage drop from B+ cable to main fuse box. Lastly, did you every replace the fuel pump relay? They like to fail in the cold and will give symptoms of a bad fuel pump, as well as bad spark.

shegarty · Post by **shegarty** » 24 Jan 2019, 04:45

I will try unplugging the air pump today and check for voltage drop. I have already tested the alternator which appears to be fine. I should have mentioned that I have also replaced the fuel pump relay.

Post by **jreed** » 24 Jan 2019, 05:17

There are multiple potential causes. I can offer up that the two times I've experienced poor start up on my '97 855 were due to worn spark plugs and a failed engine coolant temperature sensor.

The spark plugs had worn to a much wider gap than specified. This caused a rough idle. Regapping the spark plugs fixed it.

The engine coolant temperature sensor had corroded, causing it to read higher resistance, which was interpreted by the computer as colder temperature, causing the computer to supply excess fuel to the engine. This caused a rough idle with lots of black smoke in the exhaust. Replacing the ECT fixed it.

Good luck!

shegarty · Post by **shegarty** » 24 Jan 2019, 05:42

Yep, I plan to check the spark plugs as well. ECT was replaced a while ago while chasing this problem previously. I am leaning hard towards some sort of electrical short that dries out or closes as the engine warms. Hopefully I can find it today

shegarty · Post by **shegarty** » 25 Jan 2019, 10:46

Update ... changed the spark plugs and found small cracks in the insulation around two of the fuel injector connections. I repaired the cracks with some hi temp silicone sealant as they were very close to the connector. Startup this morning was markedly better but it also wasn't very cold (only -5ºC). It is supposed to get cold again this weekend so I might get a chance for a real test.

shegarty · Post by **shegarty** » 31 Jan 2019, 05:24

Solved ... looks like it was either the plugs or the fuel injector wiring harness. Starts up like a champ now even in -20C weather.