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93 850 the dreaded warm start problems, cranks but no start

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

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Jaydiesel
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Re: 93 850 the dreaded warm start problems, cranks but no start

Post by Jaydiesel » Sat May 23, 2020 3:21 pm

Have you resolved your issue yet?

93ForMe
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Re: 93 850 the dreaded warm start problems, cranks but no start

Post by 93ForMe » Sat May 23, 2020 3:46 pm

Jaydiesel wrote:
Sat May 23, 2020 3:21 pm
Have you resolved your issue yet?
Maybe. I should know tomorrow if it is good. Since I pulled the Engine Computer and put it back in, my 850 has been running and starting very rough all the time. The intermittent problem went away, now it is bad all the time! The coil arrived yesterday and I just put it in. Still really hard to start and stalled out just idling. The coil tested within spec, so I think that I can rule that out as the problem.

I then pulled both computers, pulled apart the entire computer compartment and got down to all the wiring. Some of the wires were coated with an oily substance that seemed to be leaking from the back of the computer bay. I soaked all the connections with electronics cleaner, let it dry, then blew it all out with compressed air and put it back together. After that the volvo started right up and ran very smooth. I turned it off and restarted it five times. Each time it started right up without any hesitation.

When the car reached operating temperature I did the voltage drop test between the positive battery cable and the starter motor and got a reading of 0.03V which, from what I am reading, is within spec.

So if tomorrow I can start it up, drive it two miles, turn it off and it starts again, my weird problem may be solved!

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Jaydiesel
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Re: 93 850 the dreaded warm start problems, cranks but no start

Post by Jaydiesel » Sat May 23, 2020 4:46 pm

Sounds like your getting super close. keep us posted. Interested because all the different warm start issues everyone has over the years.

93ForMe
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Re: 93 850 the dreaded warm start problems, cranks but no start

Post by 93ForMe » Sun May 24, 2020 2:37 pm

I just took it out for a test drive. It has been about 24 hours since I last started it after I cleaned the wiring in the computer bay.

It started right up first crank. No hesitation from the starter, no hard starting from the engine at all. I took it on the two mile loop in my neighborhood that I have found can cause the problem symptoms 100% of the time. My 850 accelerated so smoothly, no choppiness at all. It was also idling beautifully, very smooth. I reached the end of the loop back at my home just as the temp gauge reached center. I turned it off and waited three minutes before attempting to start.

Crank-crank-crank Catch, Chug, stop. Then just crank-crank-crank

I went inside for 30 minutes, came back out, went to start it, and it started just fine, first crank. I waited for it to warm back up to the needle at center, turned it off, waited three minutes. Starts right up, first crank, no hesitation.

I still have my problem!

I really don't think that it could be the starter at this point. It operates flawlessly and the car starts easily every time except for when I drive 2-4 miles the first time each day.

It does seem temperature related, albeit in a very narrow range. I cleaned the wiring on both the ECT side and the computer side. Perhaps somewhere along the way resistance is increasing and the car thinks it is colder than it is. Would this cause it to dump too much fuel into the warming engine which would keep it from starting?

Or maybe it is computer related?

I found en exact match for both the Engine and Ignition computer online for less than $30 combined, so since I have tried almost everything else I will try this avenue while I also look to find a wiring diagram for the ECT to see if there are more connections to spray out...

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Ocelot
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Re: 93 850 the dreaded warm start problems, cranks but no start

Post by Ocelot » Wed May 27, 2020 2:42 am

Okay, I might have a suggestion, don't know if it will work for you. I had a similar problem with a friends Ford Sierra. He replaced pretty much all parts you mentioned. But the car wouldn't start with a warm engine. We got so desperate we went to our old teacher (from the mechanics school) for help. He said to look if there's not too big a gap between the crankshaft sensor and the flywheel. When the gap is too big (and it was) the ECU doesn't get any signal. Another suggestion he gave us was to look if the camshaftsensor wasn't drowned in oil due to a faulty oil seal. We also found that the positive cable from the starter was way close to the crankshaft sensor, possibly interfering it with it's magnetism. I'm really grinding my gears trying to figure out your problem, I hope this somewhat helps!
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93ForMe
'Hij die zonder zonde is, werpe de eerste steen. Ik buk wel'. Simon Carmiggelt

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93ForMe
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Re: 93 850 the dreaded warm start problems, cranks but no start

Post by 93ForMe » Wed May 27, 2020 5:32 pm

Ocelot wrote:
Wed May 27, 2020 2:42 am
He said to look if there's not too big a gap between the crankshaft sensor and the flywheel. When the gap is too big (and it was) the ECU doesn't get any signal.
First of all, thanks for helping me think through this! This problem has been driving me crazy

Is there a way to measure this distance on an 850? The sensor just gets inserted into a hole and screwed down. I have tried two Volvo sensors, both the same length.
Another suggestion he gave us was to look if the camshaftsensor wasn't drowned in oil due to a faulty oil seal.
When I switched out the camshaft sensor, the port that it mounts in was clean and dry.
We also found that the positive cable from the starter was way close to the crankshaft sensor, possibly interfering it with it's magnetism. I'm really grinding my gears trying to figure out your problem, I hope this somewhat helps!
I have been doing my best to keep wires tied away from each other and away from heat sources wherever I can.

All your suggestions really help me. I did not know very much about the inner-workings of cars before I embarked on this problem, so every idea opens up a new path for me.

93ForMe
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Re: 93 850 the dreaded warm start problems, cranks but no start

Post by 93ForMe » Wed May 27, 2020 5:54 pm

So I have a bit of an update:

The Engine computer arrived. I installed it. No change.

I have been thinking a lot about the things that misha had said about the ECT sensor. I have cleaned the hell out of the connectors on both the ETC side and on the Computer side. However this problem just seems so temperature related, I decided to dive a bit deeper.

I pulled apart the connector that the ECT plugs into and saw that the female barrel connectors were surrounded with a translucent rubbery substance. This means that all the spaying into the connector may not have cleaned things as well as I had first thought.

https://photos.app.goo.gl/sAuQm4zu57SCzML48

At the base, this material was beginning to crumble. I cut away at it with a knife to reveal where the stranded copper wire is crimped to the barrel and saw quite a bit of green corrosion.

https://photos.app.goo.gl/A6L7hAsM6KQSJ7jXA

I soaked the barrels in vinegar for a couple of hours, then neutralized with baking soda. I then sprayed it all out with Electronics cleaner.

When I reassembled the connector, the barrels just pushed out when I tried to plug the two connectors back together because the rubbery material was no longer as long as it used to be. I probably could have thought of something better, but I just bulked up the end with electrical tape and crammed everything back together.

It had been six hours since my last test drive, so I did another two mile loop, turned my 850 off, went to start it, and it started right up!

I am not going to call it fixed yet. I am going to let it sit overnight and do the 2 mile loop in the morning under the conditions that have given me 100% start failure. We'll see what happens then...

93ForMe
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Re: 93 850 the dreaded warm start problems, cranks but no start

Post by 93ForMe » Thu May 28, 2020 3:36 pm

So this morning I fired up the 850 and did the two mile loop that has allowed me to replicate the crank but no start issue 100% of the time. I turned the car off for three minutes, then went to start it. It started right up! No hesitation at all. I think that I have finally found the issue and solved it.

What I am guessing was the source of the problem was that due to the corrosion on the wiring harness side of the ECT sensor connection, the resistance increased, causing the computer to think that the engine was cooler than it really was. When I tried to start the warm engine, the computer would dump too much gas into the combustion chamber, which would cause it to not ignite. If I waited for it to actually cool, it would start right up again.

All the other things that I fixed along the way did seem to improve things as I was doing them. I think fixing the vacuum leak, cleaning the MAF, cleaning the idle air control valve all narrowed the range of when this issue was a problem. And once the engine was heated up all the way, the range between the ECT sensor reading and the reading that the computer was getting through the corrosion was close enough that it didn't throw things off nearly as much.

If my Volvo had been in tip top shape and I lived somewhere where I needed to drive more than six miles to reach a destination, I would never know that I even had this problem until the corrosion got worse and made it not start when fully warm, I am guessing.

I wonder if this corrosion is the source of many warm/hot start issues that have been unresolved over the years?

One thing I am not too happy about was the way I repaired the female end of the ECT sensor connection. I just wrapped it in electrical tape and jammed barrels into the housing and taped it all together. I did spray the wires with DeoxIT D5, which should provide some corrosion protection, but I'm not sure how long it will last. I will probably get a connector from a junkyard and refurbish it, then splice it into my 850.

I'll do the test drive for a couple more days just to be sure before I call this completely solved, but right now I am feeling pretty good about it!

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