740 Turbo 1990 Intermittent stalling

volienteffort · Post by **volienteffort** » 08 Feb 2010, 19:23

I have already replaced the fuel filter, swapped the ignition coil and fuel pump relay, and this problem persists. The symptoms I've been experiencing may occur when just starting, or at any time during operation. The vehicle seems to operate "normally", then the engine cuts out. I have observed the tachometer drops out immediately. Sometimes the engine will just as suddenly resume operating (and the display of rpm on the tach comes back on) by itself. Sometimes the engine will come back on if I quickly depress the accelerator...other times it just dies, and all the idiot lights come on across the dash. [This vehicle has an automatic transmission. When I'm driving down the road at, say 55 mph, and the engine cuts out, it may be several seconds before the idiot lights come on showing that the engine has really "died."] I do hear the main fuel pump come on to pressurize the system when I turn the key on, and I don't think the in-tank pump is at fault...but I don't know how to prove that.
One thread mentions solder joints on a radio suppression relay, but it appears the 740 Turbo does not have this. Other posts mention a "Hall sensor" and an "ignition power boost unit" - I'm not familiar with these items. I'm also concerned with how all of this intermittent stalling might be taking a toll on my turbo (which reminds me, even when the tach drops off, if I step on the accelerator, then the needle on the gauge for the turbo will show an increase in Turbo velocity). With my limited diagnostic skills, I'm at a dead end. Any help from those of you with more skill and experience would be greatly appreciated.

Post by **billofdurham** » 09 Feb 2010, 12:25

Welcome to Matthew's Volvo Site.

One thread mentions solder joints on a radio suppression relay, but it appears the 740 Turbo does not have this

It does. It is usually mounted on, or near, the left front shock tower.

Have you checked for fault codes using the On-Board Diagnostic (OBD) in the engine compartment? This is a first step in diagnosing faults on these cars.

Bill.

volienteffort · Post by **volienteffort** » 10 Feb 2010, 07:54

Bill,
Thank you for viewing my post. Checking fault codes is beyond my scope. I will have to visit a mechanic and money is extremely tight right now. It appears the access for OBD is a plastic port with a dust cap, also by the left (driver's side, US) strut tower?
Regarding the radio interference suppression relay...I found a relay by the left strut tower, numbers printed on the top of the relay are:
VOLVO
899931 1323592-1
12V/40A
made in W.-Germany

Then, because I was looking for OBD access ports, I found on the right side (passenger, US), that what I thought was a test port was another relay, with exactly the same numbers as the ones reproduced above, that appears to have been dislodged from where it would (I think) have been clipped on the coolant expansion reservoir - which is how the Haynes repair manual (which only covers 1982 thru 1988) illustrates the location of the radio interference suppression relay on the diagram of the non-turbo model. This begs the question, are there 2 radio interference suppression relays? I am game to pry the covers off both of these and resolder solder joints.

I have to wait until later today to try to reach a mechanic who might be able to assist with checking for fault codes.

Thank you again.
Larry

Post by **billofdurham** » 10 Feb 2010, 12:31

If you are prepared to solder relays you can read fault codes. The instructions are posted in the announcements at the top of the forum. You most certainly don't need a mechanic for this. If you turn up codes you don't understand post them here for more help.

The radio suppression relay is part #1323592 as is the cooling fan relay so you have probably found both.

Unfortunately Volvo put the relays in different positions on different models. In some cases they went one better and moved the relays around on the same model with different engines. Usually on the B230FT the radio suppression relay is on the left side shock tower and the cooling fan relay is mounted on the right side on or near the coolant reservoir.

If the cooling fan works as it should the relay is OK. To test the radio suppression relay take the coolant fan relay and put it in the place of the radio suppression relay. If the engine runs normally the radio suppression relay was faulty.

Bill.

volienteffort · Post by **volienteffort** » 10 Feb 2010, 15:38

This afternoon I have removed the 2 (radio interference suppression) relays, disassembled and resoldered, reassembled and resealed with silicone RTV, and reinstalled. The stalling symptom persists (at this time I just let the engine idle in the driveway...but the failure follows the pattern already outlined in first post - tachometer reading drops to zero, etc.).
The OBD test port has 6 numbered holes under the cover, a black button marked A and a red indicator (led? - light?) marked B. A shorting plug (I presume) is attached by a short plastic cord to the dust cap. Where do I go from here? Anybody out there with suggestions, please feel free to chime in.

Larry

volienteffort · Post by **volienteffort** » 10 Feb 2010, 15:42

Bill,
Thank you, I will check the announcements later. I have to take the car that works (a Saturn) and run errands. You must have been posting your reply while I was typing my update. Thanks again, and I will keep posting updates.
Larry