Engine won't rev and hunts
 

I just picked myself up a 2.3 1990 940 GLE non-turbo in absolute pristine condition, it has 1 previous owner and he had a full service history from the main stealer (not that this means much as the air filter that was changed 14 miles ago looks worse than the one on my car from a year ago).

The issue is that the car will only idle. I have seen some other posts about this but nothing conclusive. the car starts fine and idles great but as soon as you put on any accelerator the car will hunt and surge but will not rev up enough to drive. I feel it could be either the throttle position sensor or the maf sensor but after seeing the price id like to avoid that if I can. I tested the tps and it goes from 0v to 3.72v and thats it, it doesn't gradually go up and down so I believe this is bad, although the alternator has gone too so there is only 9.5v in the car so ill check it later with a charged battery.

The maf sensor is a 5 wire so I haven't checked this yet, any info in which cables to check would be greatly appreciated.

Is there anything else that it can be? someone said the idle air control valve which I will take out and clean as thats free. just trying to rule out the easy/free stuff before having to shell out on parts I don't need as I've been there before!

Thanks in advance for any help!!

The most obvious thing is fuel pressure , easy to check with the test point valve on the fuel rail ...

Thanks for the reply! How will I know if there is enough pressure, just if theres a good squirt of fuel or will I need a gauge?

you will need a gauge , and decent garage should have one .. It should be 3.5 bar and stay the same whatever the engine load , it might be ok at idle but if it drops when you rev the engine hard that is your problem . I take it for granted you change the filter regularly !

just had a look and there doesn't seem to be anywhere to test the pressure, no valve?

The most likely cause is a split in or a loose hose between the MAF and the throttle body. This will cause exactly the symptoms you're getting.

As for your tests on the TPS, what you've got seems right as it's not a sensor but two switches, one for idle and the other for full throttle.

However, you've told us the biggest fault of all. The alternator isn't giving an output and the battery is flat. Either of those will cause erratic running and can manifest itself in a number of ways.

First thing to do is to sort the alternator, you won't get any solid conclusions on the injection with a FUBAR alternator.

Does the charge warning light come one with the key at position 2? It could be something as simple as the bulb, to prove this find the thin red wire (NOT the thick one!) on the back of the alternator, unplug it and use a piece of wire to jump it to a good earth. With the key at position 2, does the charge warning light work? If not and the other warning lights come on (bulb failure, low washer, ABS if fitted and a few others) then it suggests the bulb has failed. If the bulb works but not when the red wire is reconnected to the alternator then the voltage regulator on the back of the alternator is suspect but there could be other problems in the alternator.

The choice of the next step depends very much what you find when you investigate the alternator. There are no short cuts, you need to fix the charging problem first. Don't forget to check the belt is tight!

Thanks for your reply!! I was unsure if the alternator would affect anything as technically its only charging and didn't think it could cause so much havoc, but then again electrics aren't my strong point! As its gone and I have to order one anyway i'll wait to see if this fixes the issues before jumping to conclusions! thanks for letting me know that the TPS is okay as I thought it was bad!

ill see about the charging light and also read any codes that it may have, was just charging up the battery.

Any ideas where the best place to get an alternator would be or if I can buy a part for it instead?

Have you done the tests to confirm the alternator is faulty? It's surprising how much havoc a duff alternator (or battery) can cause on a fuel injected car.

Have a look on the alternator, there should be a green label saying Bosch 0 120 xxx yyy - the xxx yyy numbers with the 0 120 form the Bosch part number, from that you can tell exactly what alternator it is so you can be sure of getting at least the same or an uprated one. I see your location is Norwich, is the breakers yard at Hevingham Hall still going? If so, you'd probably find one there. If not, a specialist Volvo breaker on ebay or if you're lucky, someone on here breaking a car.
Then there's Lakes but that's not exactly local for you.

First you need to know what you're looking for though.

I doubt you'll have any codes or even have the plug to read them on a 1990 car, if it's LH2.2 (no cat) you won't be able to read any codes at all.

As for buying a part for your alternator, you'll need to know what part(s) you need. I could make a guess based on experience of them but sadly there are certain conditions to that guess and without seeing the alternator, i couldn't actually say for certain whether the part i'd suggest would fix it or if there is another problem already there.

Are there any auto electrical and/or starter/alternator repair services in/around Norwich these days? I know there was one but can't find him online at the moment

Okay so I charged up the battery and put it back on, I checked the battery light and this comes on when the ignition is on so the lamp is fine, if I disconnect the red wire then about 3 lights go off such as washer, lights and battery. when the car is started the battery light goes dim, almost a half brightness along with the bulb icon, washer icon and what looks like a brake light with a ! in it, the abs light is always on, the oil light and lambda light go off though, is this normal?

I took off the voltage regulator to see if the bushes had worn but they are fine, the metal strips from the bushes are a little corroded so maybe the whole thing has seen better days? I can pick up a new one for £10, could this be worth doing? I can also get a brand new alternator for £90 at euros so thought maybe its better to bight the bullet and get that if the VR doesn't work. just not sure if I should try a new regulator or go for a whole new alternator?

Another point I have noticed is the fuel is on red and the light is on, will chuck in a jerry can tomorrow.

I managed to read codes using the flashing led in the bonnet, came up with lost signal to the idle air valve but that would be because I took it off earlier.

Theres a breakers yard next to me so will give them a call in the morning just incase he has one.

the valve should be on the back end of the fuel rail which connects all the injectors together . ( The windscreen end ) usually with a blue cap . it is very much like a tyre air valve ..

I did have a look, perhaps I missed it then, ill check again in the morning.

after all these years it is probably black now :-)

if its as well kept as the rest of the car it'll be polished!

Not worth throwing a voltage reg at the alternator at all, sounds as if the rectifier has gone.
Also absolutely no point whatsoever reading codes, they'll be nonsense.

You need to sort the charging problem before you can go any further. Once that is sorted, pull fuse #1 for at least 30 seconds and replace it. Then take it for a drive and read the codes again.

No point faffing about with fuel pressures until you have the electrics right. You'll probaly find it runs fine with a decent alternator.

I did wonder if it could be the rectifier, yea probably best to just change it and have done with it, might see if any other parts places have one or I'll ring around a few breakers yards also.

You'll still need the information from that green label on the alternator, it also tells you the output which can vary enormously from 45A to 100A or even 120A on some models.

In fact, looking up the 2.3 non-turbo 940 for 1990-94 reveals there are no less than 7 different alternators fitted! They vary from 55A to 100A so there's plenty of room for error!
It's fine (and often desirable) to go up on the output but going lower can often cause problems, especially if your runs are mainly short ones or you do a lot of town driving.

I did have a look on the alternator for the green sticker but couldn't see anything. On the parts sites it says it's a 55amp alternator although I know they may not be correct, I have a feeling I saw this on there too. I'll have a propper look again in the morning but I didn't see a sticker on it, perhaps it was underneath?

It may be worth going up on the amps then as there are a few bits and bobs in the car electronics wise and I don't know what I may put in later on so better to be safe than sorry.

The breakers up the road from me has one off a diesel 960, provided it fits dimension wise and has a higher or equal amperage will it work okay?

Yes but ignore the "W" connection on it, that's only for the rev counter in a diesel as they don't have an ignition coil. If possible take your old alternator with you for positive comparison on the brackets etc.

yea I'm now taking it off just wondered as the guy on the phone sounded like because its a diesel its different but ill pop down there, cheers!

an alternator off a VW van engine isn't going to fit on a volvo engine ...

It could well be different, many of the diesels were VW engines but being German, they often used whatever Bosch had available so you might be lucky. Fingers crossed for you! :thumbs_up:

he would have just as much chance picking up a lada alternator and hoping that would fit , it is a waste of time and money , it won't :-)

I found the sticker on mine, was on the underside.
It's a Bosch 0 120 488 231
K1 14v 23/65A
3523879

Looking it up, the alternator fitted to the 90-94 960 D24TIC was also used on the red block and is 100A output - in fact the same part number is offered as a replacement.
I know it's not unheard of for certain suppliers to get things wrong (for example they list a Lucas A127 alternator as fitting my other beast - not a snowball in hells chance of that ever happening!) but from experience i'd say he's in with a good chance. :thumbs_up:

Doing a bit more double-checking, it seems the 100A alternator i quoted above is a Nippon-Denso alternator but has the same fittings as yours so if the one from the diesel is available at a sensible priceand they physically match on the brackets/mounting holes, you should be fine. Useful boost in output current as well!

Depends exactly what is fitted to that diesel 960 when you find it!

So the one fitted I'd the same size and he wants £25, said I can take it and if it works I can keep it but I have to leave mine here as he wants one with the engine.

The one fitted is Bosch 0 120 469 997
It's 31/80A
So slightly higher output that mine but should be fine!?

As long as it's the same size, you shouldn't have a problem as long as it works. It's a handy extra 15A of power there. :thumbs_up:

Perfect thanks for your help, fingers crossed it works!

Let us know how it goes! If it seems to cure the hunting, unwillingness to rev, switch off and pull fuse #1 for 30+ seconds and replace it. Then give it a test run and see what's happening. :thumbs_up:

The mini power station works!! The alternator is now charging the battery!!

Sadly though my issue of not revving has not gone with the introduction of more volts 😪 is it worth pulling the fuse still? I feel like I'm gonna be going round in circles for a while now

Excellent news on the alternator! All warning lights should have gone out on start up but the bulb check function should have lit many of them on position 2 of the key before starting.

Now would be a good time to pull fuse #1, leave it out for at least 30 seconds and then refit. While it's out, check the large diameter rubber hose between the MAF and the throttle body to make sure it's tight and has no splits or pinholes in it. Also check where any hoses tee into it such as for the AICV (idle valve) ensuring those are tight too without splits/holes etc.

Check your air filter is clean too and nothing is blocking it.

Okay will pull the fuse out and see if that changes anything. the lights are all as they were on the dash, no engine or oil, all on dimly except ABS which is bright. Is it normal for them to be dim?

I checked for leaks and couldn't see anything, puller the hose off at the air filter before the man sensor and put my hand on the end, it pretty much collapsed the hose so pretty confident there are no leaks there.

I pulled off the map sensor while running and the engine almost died but then ran badly on idle so would guess thats okay?

the throttle position sensor also tested okay and doesn't affect the running when removed so would assume thats okay?

I took off the idle air control valve to clean but its an electronic one so didn't do much, there is a slide type thing that blocks off one air port but when this "shuts" it doesn't fully shut, it leaves a slight gap, there is an adjustment screw but its glued over, should this be completely shut?

it supposedly has a service 14 miles before but the filter is dirty so I will replace this along with the plugs as these haven't been done I don't think.

my other thoughts were:
*knock sensor
*crank sensor
*cold start injector
*blocked exhaust, rusty water spitting out although this has reduced and theres lots of pressure at the tail pipe

supposedly the led computer thing can test sensors so might give this a go too.

Funny enough, i wouldn't put too much store by putting your hand over the hose and it collapsing as a check for leaks. You've got a huge vacuum pump (engine) pulling in 2.3L of air, 350 times a minute at 700rpm so will collapse the hose easily, even with leaks that would be enough to upset the MAF - doesn't take a big leak to upset it!

Knock sensor can be checked by unplugging and revving, if it still won't rev it's not that, likewise the cold start injector (if it has one, some did, others didn't) and if the CPS (Crank sensor) was faulty, it wouldn't run at all.

The MAF seems to be playing the game from what you've said so far so the most likely cause is either a blocked/collapsed cat or the carbon brush inside the dizzy cap and/or the rotor arm. Could also be loose HT leads.
Good news is if the cat has collapsed, being a 1990 model you can delete it and either just knock the innards out, cut it out and fit a straight pipe or a small resonator silencer.

There are a couple of other fuel related possibilities as well but those are less likely than what i've suggested so far.

yea I did think that was the case with the hose but I also couldn't find any leaks, i'll check again for sure.

I shall now go check the knock sensor and cold start injector (it is fitted)

The dizzy cap and arm is brand new so will check connections and bushing is okay.

How can I get away with removing the cat, won't it be an MOT issue? There is also a lambda sensor in it so this would cause an Issue too right? although it looks pre cat meaning it wouldn't change if the cat is removed.

Normally if a cold-start injector plays up and overfuels, revving it will help to ease the problem rather it not being able to rev.

Bushing? Carbon brush inside the cap, they have a habit of breaking, especially if they were fitted by someone errr.......... "not quite as sympathetic as they could be". Usually it's a crack to start with that can't be seen and then breaks later.

What year is your car? I'm sure you said it was 1990 - therefore it doesn't need a cat, whether one was factory fitted or not. Even some post-92 cars can get away without cats for various reasons, if that's the cause of your problems then removing it will release power and economy without compromising the law or MoT status.

If it has a Lambda sensor then it almost certainly has a cat. The Lambda sensor isn't used until the engine is warm so it won't cause a problem from cold, might even help once it's hot - too many people put cold running problems down to the Lambda sensor and wonder why nothing changes when they spend £££ on a new sensor and it does nothing for the problem.

*** EDIT *** Just had a thought, have you checked fuses 11 and 12? If in doubt (including if the blades are dirty/burnt/corroded) renew them. These control your fuel pumps - yes, there are two! One is in the tank, the other is underneath. If the in-tank pump isn't running, the underbody pump may struggle to get the fuel pulled through, enough to start it and let it idle but not enough to let it run properly.

Is it an estate by the way?

Okay so I have done some more playing, checked the air intake pipes again and can't feel anything anywhere, took them off and taped up one end and blowing in it hard I couldn't feel, hear or see any air coming out so confident these are air tight including the joints where the crankcase breather and idle valve join. is it normal to be able to blow straight through the idle air control valve when its off? could air be bypassing this and causing the issue?

I disconnected and reconnected the knock sensor and cold start injector which didn't help so these should be okay?

Sorry I meant to say brush, this I will check now and failing that will check the cat.

I am just grabbing some new plugs and fuses so I can renew the ones you suggest but haven't tried these yet but will do.

how do I get around taking the cat out though, surely the mot centre require it or is it because its older than a certain age?

I removed fuse 1 for a couple of minutes while checking fuse 11 and 12, both fuses are fine, 11 is labeled as internal fuel pump but 12 wasn't and no others are labeled with fuel pump either. this hasn't sorted any issues though sadly.

Idle air control valve
 

All the air that passes through the idle air control valve has also passed the LMM, hence the correct amount of fuel should be injected, irrespective of the position of th idle air control valve. It merely controls the idling speed, no mixture enrichment.
Have you checked the MAF for loose chips of foam that could have come out of the air filter box? The foam can desintegrate and if a flake is sticking to the measuring wire inside the MAF it will stop working correctly.
No LPG installed? It could in that case be running on two fuels.

Just wanted to make sure you meant the brush and not a bush, Has caused a few problems in the past!

Plugs, i prefer NGK but most reputable makes are good - Champion is not a reputable make! Make sure you check and set the gap correctly, 0.65-0.70mm, no more, no less or you will have problems. If it had a service, the plugs should be new or at least in good condition but bearing in mind the air filter, they may be on their last legs!

If you car is 1990, it DOESN'T NEED A CAT!!!

Only cars from 1992 onwards need one and sometimes even then, they don't, depending on chassis and engine codes.

For example my other beast is 1994 and is eligible for the BET Emissions test otherwise known as the non-cat test.

If you lay under the car and hit the cat with the palm of your hand, if you hear any rattles from inside it, there's a fair chance the honeycomb structure inside has collapsed.
When i say hit, i mean just hard enough to rattle it, don't hit it like you'd hit someone as if you wanted to kill them! :nah: