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Curing lawnmower syndrome, the easy way

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.

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Sommerfeldt
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Curing lawnmower syndrome, the easy way

Post by Sommerfeldt » Wed Dec 12, 2018 5:02 pm

So, I replaced my fuel pump the other day. After a harrowing hour of cleaning up spills and installing the new pump in the plastic frame, I started the car, let it run for 3 seconds, and shut it down. Result: lawnmower syndrome the next day.

Recalling something my dad said about flooded engines, I decided to try it out - put your foot to the floor, and jeep it there. Then crank it ‘till the cows come home.

I.e. gas pedal all the way to bottom, past the kickdown switch and all. Crank, crank, crank. The car WILL start, without removing plugs, messy oil and smoke. It’ll take some time, so get your starter helper or extra battery or battery charger out, but it’ll work just as well for our turbos, our NAs and whatever else.

One thing to remember - when it tries to start, keep the starter going and pedal to the metal. If you let up on either, you’re back at start (almost). It’ll smoke and sputter and the unburned fuel will reek, but I have to believe it’s better than spoonfuls of oil in your exhaust, anyway.

- S


'96 855 T5, R bumper and spoiler, Koni Yellows & blue H&R springs all 'round.

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Re: Curing lawnmower syndrome, the easy way

Post by jimmy57 » Wed Dec 12, 2018 7:16 pm

and then go drive it in a place where you can get it over 4000 rpm in some gear and do that for at least three minutes. This will rotate valves which will clean the seat and stems.
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Re: Curing lawnmower syndrome, the easy way

Post by abscate » Wed Dec 12, 2018 8:17 pm

More from guru jimmy from 2015, thank you as always Sir,
This gets described as ring seal on cylinder issue but I have several instances of techs not killing injection system and the compression will go up progressively as the succession of cylinders tested gets wetted by the fuel delivered by injectors.

The usual cause is the exh valve stem coked oil from porous guides lubing the stems and it gets heated and forms deposits. The water and fuel fog from a cold engine exhaust port will partly dissolve the coked oil and make a viscous sludge that dampens valve motion in the very tight cold valve guides. The hydraulic tappets get the opportunity overextend a bit as the valves close slowly and do not keep the usual pressure on valve tappets that keeps the hydraulic lash correction function working properly.
There is also valve seat deposits to contend with on engines in vehicles driven very easily that can be flaked off and hold exhaust valves open.
In either situation a leakdown test performed on an engine that will not start will show leakage out of exhaust side.

The plugs will get fuel fouled usually but prolonged cranking, one minute of starter operation before a rest, with thottle held wide open will usually get one started before the second full minute of starter has elapsed. With the compression low a minute of starter use is not detrimental like it would be while cranking an engine with normal compression and the higher starter load. Wide open throttle on most fuel systems cancels the initial few engine revolution cold enrichment as it is a programmed flooded condition clearing override.

Volvo's TSB fix was get it running by flood clearing, do a several minute high rev test drive to clean valve stems and seats (higher revs makes valves rotate), and fit new spark plugs with electrode designs more resistant to misfire under low compression. If the plugs don't foul and the engine ever starts and gets over 600 RPM the problem will not occur.
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Re: Curing lawnmower syndrome, the easy way

Post by Sommerfeldt » Thu Dec 13, 2018 1:23 am

Nice - I hadn't seen that post! I could only find the ones with dumping oil in cylinders and the whole ordeal.
Interesting to know what's actually happening when you start it with the throttle wide open - I just assumed there was more airflow through there, coupled with the ineffable magic of old time mechanic's tricks. :D

I guess my next stop is to get some new plugs.

- S


'96 855 T5, R bumper and spoiler, Koni Yellows & blue H&R springs all 'round.

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Re: Curing lawnmower syndrome, the easy way

Post by abscate » Thu Dec 13, 2018 8:55 pm

Somm...how long did it take before it started firing? 30-60 seconds?


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Re: Curing lawnmower syndrome, the easy way

Post by Sommerfeldt » Thu Dec 13, 2018 11:15 pm

It’s hard to tell - it took me quite a while, because I messed it up a few times. It’d start sputtering a little, and I’d let go of the starter and lighten my foot, and it’d be back to square one, essentially.

I also didn’t know how it would react to starting wide open, so I was a little nervous about it and didn’t let it get above 600 before letting up the first time it wanted to go.

If I had done everything correctly, I’d say that it would have taken somewhere from 2-5 minutes of cranking.

- S


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Re: Curing lawnmower syndrome, the easy way

Post by abscate » Fri Dec 14, 2018 2:19 am

Ouch. Followed by 24 hours of battery charge. Maybe the draw is way down with no compression


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Re: Curing lawnmower syndrome, the easy way

Post by LOB » Fri Dec 14, 2018 2:53 am

Sommerfeldt wrote:
Thu Dec 13, 2018 11:15 pm
It’s hard to tell - it took me quite a while, because I messed it up a few times. It’d start sputtering a little, and I’d let go of the starter and lighten my foot, and it’d be back to square one, essentially.

I also didn’t know how it would react to starting wide open, so I was a little nervous about it and didn’t let it get above 600 before letting up the first time it wanted to go.

If I had done everything correctly, I’d say that it would have taken somewhere from 2-5 minutes of cranking.

- S
Isn't 2-5 minutes of cranking risky? Can the starter stand 5 minutes of constant cranking?



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Re: Curing lawnmower syndrome, the easy way

Post by Sommerfeldt » Fri Dec 14, 2018 7:07 am

LOB wrote:
Fri Dec 14, 2018 2:53 am
Isn't 2-5 minutes of cranking risky? Can the starter stand 5 minutes of constant cranking?
Compared to what the starter is made for and capable of, there’s virtually no load on it when there’s no compression. You can’t crank for 5 minutes non-stop, but you can keep it going for a minute.

When this syndrome happens, you’ll notice that compression will return gradually, then building to sputtering, so the load will build on the starter as well. Taking pauses and letting the starter rest now and then isn’t a problem, as long as you don’t stop or let your foot up when the engine is trying to get going.

I think personal comfort and feel for what’s going on is a little important when doing this, but expect to crank it for about ten times the amount of time what you’re used to when starting normally. :D

I.e. I’d crank it for 30 - 50 seconds, check if the starter was warm or something was smoking, then get on it again. If I had done stuff correctly, 2-3 of those cycles would have cleared the problem.

- S


'96 855 T5, R bumper and spoiler, Koni Yellows & blue H&R springs all 'round.

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