1986 Volvo 760 Turbo underpowered when cold - Volvo Forums - Volvo Enthusiasts Forum


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Old 11-30-2017, 06:30 PM
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Default 1986 Volvo 760 Turbo underpowered when cold

Hello dear Volvo enthusiasts!
I do hope I am posting this in the right section...
Let's begin!
I am having some issues with my 1986 Volvo 760 (Turbo). I had a look all over the internet without finding someone solving that kind of problem.
Here is the thing;
When the engine is cold, I am not having a lot of power. It is like the car weighs 500 tons! My driveway is very steep and I can barely make it to the top...
However, the engine starts up very well with no rough idle. After a couple of minutes driving (10 to 20) and that the engine is warm, the car drives fine and has power!
I am kind of lost after trying quite a few things which made the car running condition better but still not optimal...
Things I have done :
-Checked the exhaust system and changed the catalytic converter which was clogged up.
-Pulled out the distributor cap and rotor, cleaned and treated them with special cleaner (Despite the parts being a bit old and worn, it made no difference to the running condition after cleaning).
-Checked the spark plugs : they are OK!
-Checked for vacuum leaks : no leaks.
-Checked the Turbo : It works properly.
-Oil and fuel filter change.
-Used 2 bottles (1 per full gas tank) of fuel injectors cleaner.
-Used an Enzyme fuel treatment.

Things I have not done:
-Checked the MAF sensor (which can be a culprit apparently).
-Checked the Ignition Coil.
-Checked the fuel injectors.

The Fuel treatment and the injectors cleaner did some good actually, the car seems to run better (the engine sounds healthier) but I still have that problem when the engine is cold.... A friend of mine who is good with cars said it could be an electrical problem, like a sensor or something.
Any help is very much appreciated!
Kind regards.
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  #2  
Old 12-01-2017, 04:33 PM
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if its an 86, it will be LH Jetronic 2.2...the ECU makes the decision to increase fuel and air based on the output from the temp sensor on the upper right hand side of the block as you look at the engine. The fact that it starts at all means the the start injector must be working which is operated off the sensor also..

The injectors will be electronic and I have found they don't go wrong. The mechanical injectors of the earlier cars would block up and idle would be lumpy. If you have a good idle then its probably not the injectors. The coil will either work or not, so its not that.

Could be the Mass Airflow sensor...they can cause poor running and rough idle/limp home mode..but it would not resolve when you warmed up the car...Unplug it and clean the contacts and look down the sensor and see if there is any rubbish on it though. I have found that a bad contact in the sensor connections can cause very poor running and lack or power...

If the system is not enriching when cold, it could be the ECU..you will beed to check the temp sensor resistance changes as it heats up...if that is OK, then it may well be the ECU...try this
https://www.autozone.com/repairguide...00c15280064193
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Old 12-01-2017, 06:17 PM
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Quote:
Originally Posted by mikesredheap View Post
if its an 86, it will be LH Jetronic 2.2...the ECU makes the decision to increase fuel and air based on the output from the temp sensor on the upper right hand side of the block as you look at the engine. The fact that it starts at all means the the start injector must be working which is operated off the sensor also..

The injectors will be electronic and I have found they don't go wrong. The mechanical injectors of the earlier cars would block up and idle would be lumpy. If you have a good idle then its probably not the injectors. The coil will either work or not, so its not that.

Could be the Mass Airflow sensor...they can cause poor running and rough idle/limp home mode..but it would not resolve when you warmed up the car...Unplug it and clean the contacts and look down the sensor and see if there is any rubbish on it though. I have found that a bad contact in the sensor connections can cause very poor running and lack or power...

If the system is not enriching when cold, it could be the ECU..you will beed to check the temp sensor resistance changes as it heats up...if that is OK, then it may well be the ECU...try this
https://www.autozone.com/repairguide...00c15280064193

Hello mikesredheap and thanks for those informations! It is very helpful
One thing about my mass air flow sensor... Today I started the car up and disconnected the MAF sensor to see if it was working properly. The idle dropped for a plit second as soon as I disconnected the sensor but quickly went back to normal. I reconnected it while the car was still running and the engine stopped. When I wanted to restart the car, it took a little push on the acceleration pedal in order to start up the engine. After that, everything went back to normal.
Does that mean something for you? Does it mean my MAF sensor is toast?

If the MAF is not the culprit, I will try to see if the ECU is.
THANKS HEAPS
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Old 12-02-2017, 05:12 AM
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disconnecting the sensor probably stops the engine making any changes to its mixture settings, so it just uses what it has and goes to default settings. When we reconnect it then gets new parameters which made it shut off...It suggests that the sensor is probably OK, but the easiest way to to check the sensor is with a meter..there are published resistances for each of the (I vaguely recall) six contacts and their resistances two each other...a digital meter should sort that. Also look down the sensor body and see if the wire is OK and does not have any crap on it...the system works through heating the wire and the airflow cooling it tells the ECU how to calibrate the airflow...when you shut off the engine, a high current is put through the wire to burn off the current...

If the resistances check out then it might be worth finding another ECU from somewhere, but you can check the resistances on the ECU contacts also, as they are all out there for that unit..If the ECU is not the prob, you can probably sell it for what you paid for it.
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Old 12-02-2017, 05:25 AM
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the X factor in all this are the connections...I had a bad contact on the maf and I just got two large plastic ties to lock it in place and no more problems...with mid eighties cars, the wiring used in Volvos was dire in quality. My 760 GLE...the wire insulation just fell off and shorted all the time...they even sold complete new harnesses the situation was so bad. I had to rewire the injection system to stop the shorting which burned out no 12 fuse. THere are old cars and their are 'modern' old cars..there are plenty of 70s cars about, but you rarely see a running 80s and early 90s car left for this reason..the problems can beat people's patience...
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Old 12-02-2017, 12:27 PM
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Thanks mikesredheap,
I also checked the injectors today with the good old screwdriver technique. I heard repeated clicking on all the injectors so that means they open and closen which is good!
I will check the MAF sensor today and clean it with MAF cleaner, I guess that will not hurt.
If it does not fix the problem, I guess I am going to have to get an ohmmeter and test those resistances.
Sounds complicated but I should be able to do it after a lot of reading.
I love this car and really want to fix it! I am learning so much stuff trying to figure out what is wrong with the engine lol.
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Old 12-03-2017, 10:32 AM
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Hi-the B230F was a great engine and the turbos (when they had the intercooler) were very fast and developed more torque than the V6...Looking at your system which I think is an LH-2.2, as I mentioned earlier, the car starts through the start injector which runs according to the thermal timer resistance, which is very high at low temps so the max start injector duration is 7 seconds at 30 below. This throws fuel into the engine to start it, but the running fuel is from the injectors (which are OK). The ECU senses the temp of the block through a sensor which is just under the injection rail in the top back of the block. It uses that to time the injectors..lower the temp, the longer the duration to enrich the mixture.

The only other temp sensor it has is the airflow sensor for the turbo. The mass air meter as I said measures air intake.

The car runs normally when warm, so the system is happy then. I reckon your problem is either the mass airflow sensor connections or the unit itself (less likely as it runs smoothly when warm) or more likely, either the ECU or the top temp sensor in the block which is telling the ECU that the block is warmer than it is, so the ECU is not opening the injectors for long enough.

So take out the sensor and test it with a meter in boiling water. If it does not have the correct parameters then replace it...they are only about 10 quid. The ECU could be at fault, but I think unless it gets wet they are very reliable

So its prob the sensor..

good luck with it
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Old 12-04-2017, 10:05 PM
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Hi mikesredheap!
Thanks again for the infos!
I will start with the temp sensor and see if it does work properly. If it does not fix the problem, I will check the MAF sensor. I live in the middle of nowhere here so I had to order some MAF sensor cleaner online lol. I noticed that the colder it gets outside, the worse the car will run when cold.
Concerning the temp sensor, I took a picture just to be sure. Which one on the picture is the sensor? The one that goes into the block I guess?
Also if I do have to get a new one, where should I order it? I found FCPeuro recently, they seem pretty good and have lots of parts!!
Again, thanks heaps!

Here is the picture:
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Old 12-05-2017, 03:56 AM
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good pic, but that is the wrong sensor I reckon...that is probably your dashboard temp sensor..you need the Engine Coolant Temp (ECT) sensor which is under intake runner 3...

https://www.volvoclub.org.uk/faq/EngineSensors.html

On the picture, the sensor underneath is the knock sensor...

So I think as your engine is B230ET you will need one of these...

https://www.ebay.co.uk/itm/Coolant-T...26.m2548.l4275


when you remove the ECT, check the number on it and get in touch with the Ebay vendor if in doubt...it has a chunky double pin plug...it might be a bit fragile after 30 years so be careful taking it off..they snap into place, so you press on the sides to release them, but they are not very accessible as you can imagine

If this does not work, its cheap ...if it does, then you are good...If you have a meter, then the sensors start at a high resistance,,about 6000 ohms which drops to about 140 or something like that...this provides info for the injection duration as well as how much the throttle bypass solenoid opens to elevate the idle when cold....if you are keen you can compare the performance of the old and new sensors with boiling water and ice etc...if they are the same, then the fault may well be the ECU...

So you have three temp sensors on the engine, the start injector timer, the ECT and the dash temp...

good luck anyway
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