Volvo 480 Club Europe

I replaced both ECU's and problem still there.

Injectors are fine as car starts after a veryyyy long while left untouch.

So, this is exactly whats happening :

1. Car starts fine & leave it to warm up
2. Turn off and try to start it again immediatley - starts OK.
3. Turn off and leave it for 15min/20min - NO START
4. Leave it for a long while , say 5hrs, try to start again - starts OK.

I am thinking some electrical / electronic component is warming up and failing when it comes to start and needs alottttt of time to cool down and work again !

NOTE : engine works flawlessly when started ! No knocking, perfect 850-900rpm idle, no smoking, etc


ITS DRIVING ME CRAZY !!!!!

So.... a little bit of progress today !

I started the car as usual & waited for it to warm up.

Turned it off and left it to rest for 15min.

Tried to start again - NO start.

Unplugged the temperature sensor and tried again! BANGGGG ... off it goes thought it was the temperature sensor so I went to the local BOSCH agent and bought a new sensor. Removed the old one, put in the new, plugged the wiring and tried to start again -- NO START !!!

When the the temperature sensor is removed or when to car is COMPLETELY COLD ! Not a single degree more ! it starts OK -- when hot it does not start, despite the brand new temperature sensor!

What other electronic component relies on the temperature sensor readings ???

NOTE: As I said in my previous posts, I already have tried a couple of spare ECU's, and still with same problem.

there are 2 engine type sensors for the 480 engine

the turbo one which has black plastic casing round the socket

the NA one which has a blue plastic casing round the socket which one have you got?

glasgowjim wrote:there are 2 engine type sensors for the 480 engine

the turbo one which has black plastic casing round the socket

the NA one which has a blue plastic casing round the socket which one have you got?

Black one -- same part number (also looks exactly the same) as the original one.

So, you say that the engine always starts when its cold, or warm but the temp sensor is unplugged. If you unplug the temp sensor, it switches to cold mode... Sooo, the engine start in cold mode. Otherwise dont. Fuel problem maybe?

grafi wrote:So, you say that the engine always starts when its cold, or warm but the temp sensor is unplugged. If you unplug the temp sensor, it switches to cold mode... Sooo, the engine start in cold mode. Otherwise dont. Fuel problem maybe?

Exactly !

Obviously it is a fueling problem as when the engine is warm, the injectors do not spray! But when cold (or with no temp sensor) they work OK.

Spark is always OK.

Already tried to replace the fuel ECU but still same problem. Also tried to replace other ECU, but still the same.

What other electrical / electronic components have to do with the fueling system ??

Did you check the wiring/connector from the coldstartsensor? Looks to me something is wrong with it, seems that the ecu isn't getting the info from the sensor when the engine is hot. The coldstartsensor from a turbo is different from a N/A engine as it provides a signal to both ecu's.

Iroll480 wrote:Did you check the wiring/connector from the coldstartsensor? Looks to me something is wrong with it, seems that the ecu isn't getting the info from the sensor when the engine is hot. The coldstartsensor from a turbo is different from a N/A engine as it provides a signal to both ecu's.

That is not the case.

Because right after I start the car without the sensor, then I plug it again so it can work correctly, because when hot and without the senor it works really rough, obviously.

Just an outside chance check the wiring to the cold start sensor for continuity . Eliminates 1 possibility.

glasgowjim wrote:Just an outside chance check the wiring to the cold start sensor for continuity . Eliminates 1 possibility.

Exactly, why wouldn´t you want to check it? Start eliminating everything.

Yes i can. And i will.

But what i mean is that if the wiring is cut, then the engine would not make any difference (when hot) when i plug the sensor again once its started.

When hot i start it without sensor, and it works very rich and high idle. Then i plug sensor again, with engine still running, and it corrects idle and fuel. So the temp sensor is sure to work.

BUT will check still !

I was also thinking, if the wiring for the temp sensor is cut, then the ECU(s) would think that the engine is cold.

Now, with temperature sensor unplugged, simulating a cold engine, it starts immediatley. So, if the wiring is incorrect, it should start anyways, but work rough and on a high idle once the engine is warmed up.

Just a thought, still will check the wiring when I have time. Pin 2 on both ECUs, right ?

According to your informations (replug the sensor corrects the fuel amount) the wiring should be ok, because it corrects the cold mode (too much fuel).
Obviously during the start only in cold mode gets the engine the right amount of fuel. Somehow the injectors dont work properly during start.

(Tomorrow will be the 15th Hungarian Volvo Gathering, I will ask around about your problem, maybe someone met something like this before. )

grafi wrote:According to your informations (replug the sensor corrects the fuel amount) the wiring should be ok, because it corrects the cold mode (too much fuel).
Obviously during the start only in cold mode gets the engine the right amount of fuel. Somehow the injectors dont work properly during start.

(Tomorrow will be the 15th Hungarian Volvo Gathering, I will ask around about your problem, maybe someone met something like this before. )

Exactly !

Ok, thanks a lot

Maybe a too high resistance in the wiring, this will feed the ecu with the wrong info. Would explain that the sensor is influencing the idle, but not right enbough to start it when hot.
I haven't read the whole topic, but did you also checked the MAF sensor and the airintake temp sensor?

Iroll480 wrote:Maybe a too high resistance in the wiring, this will feed the ecu with the wrong info. Would explain that the sensor is influencing the idle, but not right enbough to start it when hot.
I haven't read the whole topic, but did you also checked the MAF sensor and the airintake temp sensor?

How can I check the MAF sensor ?

and is the air intake temp sensor plugged just before the turbo ? on the rubber elbow..

Here is a drawing at which pins you have to measure the resistance from the MAF (luftmengenmesser). I only have it available in German, but the pics and resistance values speak for themselve I hope! The 382 ohms is just a starting point, most turbo's have the resistance set higher for better power and more economical driving. Inside the maf there's an CO adjusting screw for the settings, so best is to change the settings and check them with later with a CO meter to prevent it from running too lean.

Cant understand where I need to check for the resistance tho

Can you explain to me the procedure in some simple terms please ?

I am more of a mechanical person then electrical

Iroll
even zooming up you cant read the diagram as the numbers are too small to read

Temp. sensor wiring is OK, just checked it!