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.

 

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

 

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.

 

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...

 

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.

 

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

 

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:

 

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

 

UPDATE on the underpowered volvo!
So, since the last message, I did quite a bit of work on the 760.
Here is what I did :
- I did clean the Mass air flow sensor which was actually dirty so it did some good but the problem was still here.
- I put a new ECT sensor in and same thing, no changes at all!
- I cleaned the throttle body and that did some good but did not fix the problem.
- Put a brand new distributor in. No changes at all.
I don't really know what to think anymore... The car is sluggish when cold and does not have power at low rpms when warm. The car starts to have some pull at 2000-2500 rpms.
I noticed something when I was cleaning the Throttle Body though.
I checked all the sensor connections and they were all good except one. There is a sensor as seen on the picture that had a broken pin (3 pins in total on that sensor)... I don't know what that sensor is, RPM sensor??
Could that be the culprit?
Any help is VERY MUCH appreciated!
Thanks

 

OK...the connection on the left looks like the knock sensor...there are listed specs for them in terms of resistance etc, but not sure if that is the problem, but worth checking that there is continuity with the ECU...the other more obvious solutions that you might have tried include..

the intake airbox has a thermostat that sticks and you either get cold air when it is starting (you need pre-warmed air from the manifold to assist when warming up) or hot air when you need cold air during normal running..they often fail after a few decades..

Also, another obvious one...all the hoses...any vacuum problems and engine idle etc will be poor or lumpy...I think your injectors are OK?

Also, I have forgotten..what is the cold idle like...is it very lumpy and lower than it should be?

For start up you need the ECU to measure the temp (we know its got good temp data, from the new sensor) then it has to enrich the mixture (injectors throw more fuel in, ECU tells them to do that) and you need adequate fuel line pressure to get that to work.

Also, you need more air from the throttle bypass solenoid...

So I assume you have checked the operation of the solenoid...you can get the ECU to test it for you but they can be taken off and cleaned easily with WD-40.

Fuel line pressure...there is a diaphram that is vac controlled that modulates line pressure...check for leaks in that. If you disconnect it and (sounds nasty but it works) put some tubing on it and check it is not leaking and holds a vac (no petrol should be sucked up)...then the fuel pressure should be properly controlled...

also, the old cars have two fuel pumps...a main pump under the passenger seat and a pick-up pump in the tank...if the pick-up pump is failing you get stuttering fuel pressure if the tank is half full or less....

Finally, it could be an ECU problem..you can get turbo ECUs with the same config as yours on ebay for not very much...might be worth buying one anyway...

Mike

 

with the fuel pressure regulator..I mean that you suck on the hose you attach to it and you should not get a petrol taste..if you get fuel then it is leaking...they are pretty cheap on ebay second hand..about 20 quid ish...you might bag an ECU for a similar amount if you are lucky

 

Hi Mikesredheap,
It looks like the idle is acting funny when cold now, not like before.
I think that is because of a bad connector on that canister shaped sensor (as seen on the picture right in the middle / is it the RPM sensor by the way?). I think that was causing the idle problem because as soon as I touched it a little, the idle went from very low and rough to normal.

Concerning the ongoing problem, I recently ordered an oxygen sensor as well as new plugs. Let's see if that makes the condition better!
The car is underpowered when cold but also when warm. I don't have much power especially at low rpms... I can floor the pedal when starting the car and it will take off reeeeeaaaly slow.
I checked my injectors again and they do work properly!
If the O2 sensor does not make a difference, I think I might get a new ECU in the nearest volvo junkyard.
Anyway, let's see what happens with the new sensor and plugs.
Will update the situation afterwards!

 

Hi...good to see you are not giving up...welcome to the nightmare of the recurring old car with modern injection system problems!

The cannister thing is the throttle by-pass solenoid...if you take it off, you can see that it has tubes across it that act as a sort of valve for a hose that bypasses the intake manifold..the solenoid turns a circular shutter which is fully open when the car starts from cold and then gradually occludes as the car warms. It allows enough air in to keep the engine idling at the level required to prevent stalling when cold and also to allow in enough to maintain idle speed due to other factors a cold engine has ...the ECU temp sensor sends info to the computer which then decides how far to open/shut the solenoid. You can take them off and then blow some WD-40 down the pipes and you can see that the shutter is moving easily. There are two versions on Volvos...the early three pin and the later two pin type. The later type is far more robust and never fails..I would give it a clean though.


O2 sensor...well, if the engine is getting a message from the sensor that there is loads of oxygen in the exhaust (leak in the manifold for example) then it will throw in loads of fuel and run really rich. If the reverse happens it might run very lean indeed....The sensor can be tested (and its wiring) and its voltage is very low but can be measured..there are published specs for them. They can fail if they get coated with silicones or other crap. A new one is about 30 quid...Very lean mixture could give you the low power symptoms..so this is a possible, but it would be cheaper to test it than just replace it, but testing is a faff and once you replace it then you know there is no problem provided there is a voltage in the wiring-maybe check that first before you do anything, even though it is a pain getting under the car. Removing the sensors is not always easy as the environment is very harsh indeed down there. If you struggle, heat the area with a propane torch and warm the sensor, then stick some ice on the sensor alone which should contract it..then it should come off

 

The ECU replacement is a last resort, but bear in mind that you can sell them for 20-40 quid if its not the problem. When changing it...DO DISCONNECT THE BATTERY FIRST...I know someone who didn't do this and fried his ECU. Also, make sure there is no static about etc. They are fragile..also...any ECU you find now is ten years older than my student son...so this stuff is really way past its sell-by...there are places that recon them for about 150 quid though...The ECU is tucked away near your right foot where you drive, behind the plastic cover. When you remove it (annoying litte torx screws) you can take the opportunity to test continuity in wiring connections to all the main sensors from the ECU main connector through to each unit...

 

UPDATE
So I took the throttle bypass solenoid, cleaned it and it did fix the idle problem. Now the idle is no longer acting up although it is a little bit high (1000rpms) even is the idle speed adjuster is screwed all the way in...
I can live with a high idle for now.
I also changed the plugs, being really precise and careful about the gapping and it made no difference. I once again made sure the 4 injectors were good and it was the case. The 4 cylinders are firing properly. I checked for vaccum leaks again and there were none!
I did the fuel pressure regulator trick and I had no petrol taste...
When starting the car, I can hear the fuel pump starting and whirring so I don't think there is something wrong with it.
So if air, fuel and spark are not the problem. Then it must be an ECU issue right??
Could it be a timing or compression problem??

I got that new O2 sensor for a good price so for now, I will change it and see what happens. I REAAAAALLY hope that will fix that damn car!
I have been thinking about this problem over and over again... Sometimes I think, what if it was simply something disconnected?? A bad fuse?? God I don't know lol
BTW, by ECU is by my left foot. I live in Canada so it is probably why
The quest continue!

 

hi i was having some similar issues with my 1996 960, i replaced everything over the last few years and even rebuild the engine and transmission....and to no avail when the temps dropped below 32, the wagon felt like a ship that ran aground. i just swapped th ecu with one i got on ebay for 11 bucks.....now no issues what so ever, idle is sitting pretty and the car has power when cold.....

PS 1996 wagon with 250K

 

I seem to recall on the later versions of the LH2.4 ECU system the idle was set by the ECU itself and you could not adjust it (you can't on mine which is a 1990 model). The high (ish) idle is a clue and with a previous ECU on my car, the idle would increase randomly and then cut out. I would re-start and no problem for a few days, then it would happen again. If your car has air-con or is an automatic, you should see the revs drop slightly when you put the car in drive (and/or switch on the air con). That shows the system is responding to load. You can check the TPS (throttle position sensor) output, which tells the ECU what you are doing with your foot...best to test the output in situ as its a pain to set them correctly to get them back on again.
I think on balance its an ECU issue (if the O2 sensor does not fix it). As I mentioned in an earlier post, they are all very old now, but surprisingly tough. If you do replace it, obviously try to find one with an identifical Bosch code to the one you have, but if you can't find the exact one, there are several variants that will run your car. As I said, if you do change it, disconnect the battery and try to ensure that there is no static discharge possibility. If you are in Canada, I guess poor running in the cold is a very relevant issue indeed!My grandfather lived in Montreal for a while and half my grandmother's family emigrated there before WWI...it was a very popular destination then. None of my grandmother's brothers ever came back, so it must be pretty good.

 

meant to say that when the revs drop, they increase again under load..

 

Hum... Interesting! I certainly don't want to go down that path! Rebuilding a transmission is a costly mission lol
Thanks for your help!