96 850T5 Hard restart after engine is hot in hot weather.

[redbeak1]

Hi redbeak1,
I am having similar issues, and I think I may have had a break-though with it today.

My problem seemed very temperature related, but I had switched out the ECT sensor and they persisted. Today I pulled apart the female connector that the ECT plugs into and found that the sheath around the female barrel connectors had started to break down. I cut it away at the base and found a whole lot of corrosion that I cleaned out. Corrosion will increase resistance and make your car think that it is colder than it is. Cold starts, no problem. Hot starts, problem.

Here is my thread, I have a couple of links to pictures of the connector:

viewtopic.php?f=1&t=93975&start=20#p543693

That's a good point. Corrosion on this connector is very common on 850s, it's definitely worth a careful look.

Anytime I have a connection apart, I've been using ACF 50 spray for everything. My brother flies small aircraft, and they use this stuff on just about everything to prevent corrosion. I also spray the bottom of my Volvo and motorcycle to prevent the salt from rusting. It's safe to use on electrical connections, solenoids etc...

[93ForMe]

Anytime I have a connection apart, I've been using ACF 50 spray for everything. My brother flies small aircraft, and they use this stuff on just about everything to prevent corrosion. I also spray the bottom of my Volvo and motorcycle to prevent the salt from rusting. It's safe to use on electrical connections, solenoids etc...

The thing that I found out about the corrosion on the wiring harness side of the ECT sensor is that just spraying it when the connectors are apart can not reach the corrosion because of the translucent rubbery sheath that surrounds the female barrels. You have to pull apart the plastic housing, pull out the barrels, then cut away at the rubbery sheath to expose where the copper stranded wires are connected to the brass barrels. Only then can you reach the corrosion. I had sprayed the heck out of it on both sides before I did the full disassembly and it didn't change a thing. After I had it all apart and stripped down I was able to remove all corrosion so that the resistance readings from the ECT sensor were able to reach the computer without being substantially elevated by corrosion.

[redbeak1]

96 ForMe, Your situation is different since the entire connection has deteriorated. I meant to say to use the ACF50 as a preventative in the future. I did take apart my ECT connection based on your findings, unfortunately my connection was very intact. Misha has given me a new direction regarding the purge valve. Since you repaired your ECT connection, have you been able to test the car? Please let us know if you solve this.

[93ForMe]

The connector did not appear to be deteriorated until I took it apart. The far end of the barrel sheath was only beginning to crack a little. Only when I cut it away did I reveal the corrosion underneath.

Now that I have cleaned away the corrosion, my hot start issue is gone. I tried replacing just about everything else, but the problem persisted until I cleaned this corrosion.

Here is a photo of the connector partially dissembled, you can see where I started cutting away at the sheathing:

https://photos.app.goo.gl/7v2FAHGLmyguqeRKA

once the barrels are out, it is easy to cut away to reveal the wire. Note the green corrosion:

https://photos.app.goo.gl/o4eN3VZRgLik1LQD6

If you do go this route, just be aware that once you cut away the sheath, the barrels will need something to offer resistance where the sheathing once was in order to not be pushed out the back end of the plastic connector once you reconnect the female to the male connector. That is why I only stripped the sheath back only enough to reveal the bare wire. I then used electrical tape to bulk up the area that I had cut away.

When I think about it it makes sense. Why will the car start fine cold, but not warm? The ETC reads high resistance when cold, and low resistance when warm. The corrosion increases resistance, making the car think that the engine is colder than it is. Because it thinks it is cold, it dumps too much fuel, which in turn prevents combustion in the warm engine. Only waiting until the engine is actually cooler will allow you to start it.

[redbeak1]

Wow!! not an easy problem to find. Awesome troubleshooting. Without the help of this forum, I doubt I can keep my car running this long. Some of these guys, can tell you what's wrong with your car standing 20 feet away from it!!
So your problem is solved. When I find my issue, I'll post it also.

[abscate]

Wow!! not an easy problem to find. Awesome troubleshooting. Without the help of this forum, I doubt I can keep my car running this long. Some of these guys, can tell you what's wrong with your car standing 20 feet away from it!!
So your problem is solved. When I find my issue, I'll post it also.

There is some real talent, wisdom, and experience here. Kally once told me where to find a rare M7 intake manifold bolt I dropped, down to which recess in the engine it would be located.

[bmdubya1198]

When you work on these as often as a lot of us do, you get to a point where you recognize every piece of hardware, and every recess in the engine. And (sometimes) you can diagnose problems with the most vague descriptions.

[93ForMe]

Wow!! not an easy problem to find. Awesome troubleshooting. Without the help of this forum, I doubt I can keep my car running this long. Some of these guys, can tell you what's wrong with your car standing 20 feet away from it!!
So your problem is solved. When I find my issue, I'll post it also.

Good luck with your restart problem, I am eager to hear how it turns out!

[redbeak1]

Just checked mine.....closed in both directions when engine is not running.

Your's could be failing....since it's closed in just one direction.

Here you can see that a good evap valve is closed in both directions:
https://volvo850wagon.wordpress.com/tag/evap/

Replaced Evap purge valve, but problem still persists. There is a check valve on the canister side of the purge valve in the hose. Could this be an issue? Do you think that 38 psi(at the rail) is enough to push through fuel vapors. Manual states 43 psi .Not sure if engine is on or off.

[bmdubya1198]

Try blowing through the check valve to test it. They do occasionally fail, I've had them fail before.