Hot start issue HELP!!!!! Calling all experts.

[markf]

Hi All, I am desperately in need of guidance and advice. I have a 99 c70 t5 manual trans with 140k. All stock except IPD full exhaust and radio.

I have a warm/hot start issue. When the car is cold, the car will generally start pretty easy most times on the first crank but always by the 2nd crank. But when it is warmed up, it is very difficult to start. Sometimes having to crank it 4-5 times to start while other times it just won't start until the engine is cold.
Here is what has been done some chasing this issue, some general maintenance: fuel pump replaced, crank position sensor replaced (and double checked to make sure it is not a bad part) the ecu, keys, and fobs were sent to Xemodex as my mechanic thought that was the issue.
The immobolizer ring was replaced and he has gone thru checking grounds.
He is an excellent mechanic, and owns the largest Volvo specialty shop in Albuquerque so he definitely knows Volvo.

My mechanic is at a loss as to what to do next. The car is not my daily driver, it is a nice weather toy but it now has been at the shop for over 2 months.

Any suggestions you have that I can pass on to him?

[Baffler]

Engine Management Light on? Any fault codes present or any other running issues leading up to problem?

A couple of things spring to mind:

1) Out of range Engine Coolant Temp sensor. You can test for resistance using a multimeter ~ 2.5k Ohms when cold reducing to ~ 200 Ohms when hot.

2) Failing Camshaft Position Sensor going out or range when warm.

3) Failing fuel pump relay or poor contacts at the fuse box.

4) Weak Fuel Pressure Regulator diaphragm at the fuel rail.

Just throwing out some ideas for you...other members will have more....although it may be slow around here today as there's something of a party going on down in London Town.

[Luxobarge]

^^^WHS^^^

Especially the coolant temperature sensor, you have classic symptoms of this. Check/clean the connections to it too, not just the sensor itself. The same sensor is used for ECU engine management AND the temperature guage, so if the guage is not reading as it normally would, this is a massive indicator of a fault, but even if it's reading correctly it could still be that.

Baffler's other suggestions are good ones too.

Just one thing - with faults like this, try to test and diagnose thoroughly, rather than just throw parts at it in the hope that something will fix it, because doing this it's all too easy to introduce additional faults.

Yes, we need to know if the EML is on, one way or the other this will include/exclude a number of possible causes. If it's on, you REALLY need to read the codes, this will tell you a lot.

[markf]

Thank you for the reply. The only code was intermittent. It was for a camshaft position sensor so my mechanic replaced it.

[Luxobarge]

OK, useful to know.

Re. my previous comments, remember that most of the time a faulty CTS won't throw a code, it's just telling the engine it's cold when it isn't or vice-versa. It'll only throw a code when the values seen by the ECU are way out of range, or "implausible".

[Alpine]

I had similar symptoms on my previous S70 and it was the coolant temperature sensor

[vanno]

Hi there!

I am assuming by now that you have solved this issue but my son had exactly the same issue with his 1997 S70 2.5. Several garages had a go and nobody could fix the issue. It seamed logical that the coolant temperature sensor was at fault particularly when we spotted a bare wire but after it was replaced still no joy. Finally, I had a brainwave and changed the distributor cap, rotor and plug leads and yes, this cured the issue. Actually, inside the cap was disgusting, however it continued to function was a minor miracle! So, if this doesn’t help you, it may help someone else who is experiencing the same problem. Blessings my friend.

[Tannaton]

Originally Posted by vanno

Hi there!

I am assuming by now that you have solved this issue but my son had exactly the same issue with his 1997 S70 2.5. Several garages had a go and nobody could fix the issue. It seamed logical that the coolant temperature sensor was at fault particularly when we spotted a bare wire but after it was replaced still no joy. Finally, I had a brainwave and changed the distributor cap, rotor and plug leads and yes, this cured the issue. Actually, inside the cap was disgusting, however it continued to function was a minor miracle! So, if this doesn’t help you, it may help someone else who is experiencing the same problem. Blessings my friend.

If it is persistently difficult to start from hot - that will likely be either low fuel pressure or no spark (latter usually due to immobiliser issue). I have seen once before on these cars the fuel rail pressure sensor give erroneous readings when hot after the car has been stood - when the engine is running, cold fuel is being constantly pumped through the rail and bled back to the tank so the rail remains relatively cool. But when the engine is switched off for 5-10 mins, the heat soak in the engine bay causes it to get much warmer than it would with the engine running.

[CSCUK]

The fix for failing to start/rev once hot for my 1999 v70 2.5 petrol was to remove the distributor and clean the distributor and rotor arm contacts with the blade of a screwdriver.

It now revs correctly when hot. Prior to cleaning contacts the motor died as soon as the accelerator was pressed then struggled to start again while still hot, and only when cool again started reliably.

Hope this works on yours.