Hello, I am right now experiencing an intermittent engine problem with a 1987 VOLVO 740 TURBO.


Sometimes the car starts fine and drives fine, other times the engine is hard to start, once started it runs like crap, so much so that you have to keep your foot on the gas pedal 1/3 (sweet spot) to the floor just to keep the rpm's high enough so it doesn't stall. If you try to drive it during this symptom there is heavy misfiring, pre ignition causing detonation in cylinders and the car lacks power and will not accelerate worth a damn, if you gradually depress the gas pedal you can barely accelerate under this condition; that is until the transmission down shifts into the next gear and the engine starts coughing and suffering again with the increased load condition imparted upon the crankshaft. Other times when the problem is not manifesting itself there is full engine power and the vehicle idles and runs beautifully.


So far I have checked...


fuel pressure (50 psi constant regardless of throttle position and engine load). Observation; I blocked the return line at the fuel rail and removed the jumper wire to shut the pump down. Fuel rail is now holding 50 psi, began cranking engine, fuel pressure began to fall with each crank of the engine, it stopped falling at the fifth or sixth crank and sat at about 25 or 30 psi. does this indicate clogged injectors?


Battery terminals clean and tight.


Checked the ground connections at the intake manifold and measured 2 ohms resistance.


Computer grounds at passenger side kick panel 2 ohms resistance.


Auxiliary air valve functions.

Throttle position switch opens and closes as throttle valve is opened.


Replaced the ignition module with a used unit, no effect, possible the used unit is also defective, not certain.


Tried jiggling the engine wiring harness around while engine was running crappy, no effect.

 

No it doesn't indicate blocked injectors. That test tells you nothing. Injectors don't just block and unblock, you have an electrical issue or sensor issue.


Regards, Andrew.

 

I have a 1987 740 turbo too. Gremlins are hard to trace.
In order:
1) Replace air filter. I had black smoke and difficulty going up small hills. Finally, replaced the air filter and problems disappeared.
2) Do a tune-up. Replace distributor rotor, cap, spark plugs, and spark plug wires.
3) Check for oil leakage at the Hall sensor plug. If too much oil gets on the Hall sensor plug, it can cause a short circuit that will fry the Hall sensor. Symptoms of a failing Hall sensor are hard starts and intermittent no-starts until it fails completely, in which case you will have a no-start all the time. If oil is present, check condition of Hall plug wires and replace the green O-ring on shaft for distributor plate. More info can be found at www.stepbystepvolvo.com.

 

I'd think it's electric rather than fuel related. '87 can have bad disintegrating wiring that may cause all kinds of weirdness. Any evidence of flaking wires under the intake manifold, for example? I'd look at the the Power Stage also...

 

Thank you tedv, fredbyte and (typhoon aka Andrew)

to tedv,
yes there is flaking wiring under the hood due to age and deterioration, have noticed this at the ignition coil primary wiring, However, I seem to be getting a nice clean blue spark at all the cylinders 1 through 4. so I did not think much of it and taped the exposed copper back up with electrical tape.

I checked the primary and secondary resistance of the coil. If I recall correctly, I measured 5 and 7160 ohms respectively. measured infinite ohms at the primary/secondary and ground when the coil was disconnected. thus no internal short circuits.

The temperature sensor for the instrument cluster was also flaking due to age and deterioration, repaired this section of the wiring and instrument cluster gauge now indicates correct engine temperature.


To Fredbyte,
I failed to mention a few things on my original post.
I have not replaced but checked the air filter, it appeared flawlessly clean. When held up to a light source, could see the light shining through the fibers of the filter. thus I believe it to be in good working order.

I have also conducted a full tune up. Replace distributor, rotor, cap, spark plugs, and spark plug wires. No effect to the problem that still exists.

I have also noted your concern for the hall sensor as a possible culprit, I have not investigated this to far as a possibility since I assumed the hall sensor would either work or not work at all, did not expect "hard starting and intermittent no starts" to be indicative of a sensor in initial stages of failure.

Other than checking for oil leaks at the distributor o ring, is there any other means of bench testing the sensor to see if it is in fact the culprit?
Currently there are no Volvo's of the same engine family at my local automotive recyclers and would have to buy the part new if I suspected it.



At this point I do suspect it as a very high possibility, I just wanted to be more sure before buying the new part.



To Andrew
Regarding the injectors, I couldn't agree with you more, the fault I am experiencing is intermittent, is present some of the time and not other times,

whereas clogged injectors would present the engine problem all the time, that is 100% of the time.

I only thought it pertinent information to mention due to my experience with a 2.8 liter GM engine I once took the fuel pressure of. leak down test blocking return to the tank; each crank of the engine brought the fuel rail pressure down until the fifth crank, it was at 0psi. whereas the Volvo B230FT engine the leak down test of the injectors. stopped falling at 30psi for some reason.

Whatever this observation is, I am willing to rule it out for the time being since I do not feel it is my problem, as you have indicated "... Injectors don't just block and unblock, you have an electrical issue or sensor issue."
I am leaning for the time being more towards fredbyte's concern for the hall sensor on the distributor.


Again, a thank you to all your prompt replies, I will keep you posted as I get around to checking the engine some more.


Regards Arjun

 

I think Tedv is on the right track, this is an intermittent fault.
What you could try is shaking the wiring harnesses whilst the engine is running and see what happens. If it goes funny, keep moving closer to various connections whilst wiggling the wiring.
Hall sensors do go bad in funny ways, I've had a couple on various cars get weak, also, checking the air gap between the Hall sensor and the reluctor is always worthwhile, I had apoor running car once and the pickup was far too far from the reluctor, a weak signal was the result.

Regards, Andrew.

 

My air filter looked fine too. If yours is a few years old, it is minimal cost and effort to replace. It will probably help.

Do you have oil droplets on your Hall plug? Go to www.stepbystepvolvo.com and click on replacing the Hall sensor plug. Lots of info in there. A replacement Hall distributor is pretty cheap at the junkyard.

 

To Andrew

On my initial post I had attempted to "...jiggling the engine wiring harness around..." tried this to see if anything happened, even went further by trying this at all the sensors on the engine, knock, coolant temperature, mass air flow, lambda, hall sensors, throttle switch and air bypass valve, unfortunatly nothing changed and I was still left with the same problem.

Got around to removing the distributor yesterday.

The gap between the reluctor wheel and the hall sensor on this particular make and modal is not adjustable. Hall sensor is fussed to the base plate of the distributor by two long aluminum pins that pass through the hall sensor mounting holes and are welded to the base plate of the distributor. No provision for adjustment exists.

On visual inspection the reluctor wheel seems to have a minimal gap at the hall sensor. Thus I believe the gap to be acceptable.



TO fredbyte

I have read the information available at the site you provided me, thank you, it has been most informative, I particularly took note of the description on checking the hall sensor wiring harness running back to the ignition computer for shorts or breaks before removing the distributor, I followed through on the procedure and found the harness to be in good working order. I followed through and removed the distributor for visual inspection.

I do not have oil droplets on the plug of the distributor but upon removal of the cap, rotor, and the dust cover, I have found the inside of the distributor base plate and hall sensor covered in a thin layer of oil. I do not know if this is cause for alarm or not.
Can hall sensors fail due to oil depositing on them over a number of years?


Unfortunatly as stated in my previous post, "Currently there are no Volvo's of the same engine family at my local automotive recyclers and would have to buy the part new if I suspected it."


Arjun

 

Not sure about failure of Hall sensor if there is oil on the sensor itself. Intermittent problems are difficult to analyze. You may have to just wait until the engine is in permanent no-start mode. That way, your conditions are constant and the problem is easier to diagnose.

 

I have a 740 turbo with euro lights and in black paint ,photo to come later.However I had driveability issues until I replaced the Hall sensor in the distributor.I also had a plugged cat and when that was replaced the car came alive!(rubber on demand alive).Now that was a huge step forward but I have a fuel pump issue that is bugging me.If I sit at a light too long the front pump gets noisy and the car will eventually stall.If I drive on the highway it's quiet and works fine so I don't really know what the tank pump is up to ,but I know it is working some of the time.The electrical to both pumps checks out fine

 

Alright, So I reassembled the distributor and reinstalled it in the vehicle.
Since I did not find anything wrong with the hall sensor I did not suspect it any longer. I base this on a procedure I found for checking the "ignition system" and Subsection "hall sensor". I found the procedure on shopkey5tm available for free use at Partsorce stores in Canada.

After reinstalling the distributor the problem got worse. It used to be, before distributor was removed the car would start and idle like crap, When pressing on the gas the engine would backfire and struglle to accelerate.

Now However...

The car starts but 30 seconds of idling it dies. There is far more back firing now than there use to be at idle, and every third or fourth attempt at restarting the engine the starter motor stops rotating DEAD IN ITS TRACKS. (What I think is happening...The starter motor wants to rotate engine crank shaft one direction, a pre ignition in one or more cylinders send the crankshaft in the other direction causing starter motor and crank rotation to freeze.) This is what I think is happening.

To swedeweels
Is what I observed as previously outlined an ignition problem or perhaps as you have suggested, an indication of a clogged Catalytic converter? (Exhaust gas backing up into cylinder from clogged catalytic converter until starter motor can not rotate crank due to excesive pressure past exhaust valve?)

If this is the case, would there be back firing?

If this is the case, would there not be a gradual slow down of the starter motor before freezing rotation?

I am not experiencing a gradual slow down of the starter motor before freeze, I am experiencing full cranking speed followed by an immediate
freeze. Although I do not refuse your theory, I would think that my theory of pre ignition while cranking would thus hold over your theory of a clogged catalytic converter since there is no reduction of cranking speed before freezing/stopping.

As I understand, a clogged catalytic converter can cause an exhaust manifold and or down pipe to glow dark cherry red color as the metal approaches melting point due to increased temperature brought on by increased pressure. Is this what You saw when your catalytic converter was clogged? (I am not seeing this on my car)

Further to my case, when the engine was still running before pulling the distributor a week ago. I could still hear the turbo spinning up and spinning down as the engine rpm was varied. does this suggest there is non restricted flow of exhaust gases (could hear it with the use of a mechanics stetha-scope)

I look forward to all your replies. thanks in advance

Arjun Sinha

 

The procedure I followed for testing the hall sensor...


Found step by step directions for testing the hall sensor.


10 Check voltage supply to hall sensor. Disconnect connector from
distributor. Turn on ignition. Measure voltage between red (+) lead
and ground. Correct voltage = 12 Volt
(This checks Ignition computer is sending power to hall sensor, thus, it is checking ignition computer)

11 Check output wire from hall sensor. Measure voltage between
terminal 0 (blue wire) and ground. correct voltage approx 5 volts, Turn of ignition.
(this step checks that internal resistance of hall sensor windings is correct. OHMS LAW It checks for absence or presence of internal shorts or opens in the hall sensor)

12 Check distributor ground. Measure resistance between terminal 1
(black (-)) on distributor connector and ground. Correct resistance = 0 ohms, reconnect connector to distributor
(checks integrity of wiring harness and ignition computer ground.)

Side note
Testing at ignition control unit Remove panel from left side of pedal in
footwell. Lift out control unit. Remove connector cover and side
plate. reassemble connector to prevent damage to ignition control unit.

Hall sensor check
13 Check Hall Pick-Up Disconnect red/white and blue wires from
ignition coil to prevent arcing. Measure voltage between ground and
terminal 24 of ignition computer at rear of ignition computer connector.

a) Turn on ignition, Turn crank shaft with a wrench. Each time trigger wheel vane passes Hall pick up, volt meter should be more than 1.8 volts.

b) voltage should drop to 0 - 0.7 volts between vanes.

If other voltage = Defective hall pickup. Install new pick up.

 

it might be a bad o2 sensor. My car would putter and miss and have no power unless you went slow accelerating.
Check is easy just pull the code from the little box on the back of the driver wheel well. I think the code is 212

 

To Sofob0909

How do you retrieve codes on these vehicles? I haven't been able to figure that one out, do you need to purchase a scan tool? Where is the connector to plug it in located?

Arjun Sinha

 

Be sure you inserted the distributor baseplate back into the cylinder head correctly. The key is offset. If done incorrectly, you will have a noticeable gap between the baseplate and back of valve cover. In that case, you will have to remove the distributor and turn the key 180 degrees and then reinsert.