740: Car cuts off momentarily while driving

[just dave]

My wife drives a '91 740T and this past week she has complained that when she is driving the car will cut off while she is driving just for a fraction of a second. She said she can feel it and see the tach drop. It has also died a couple of times when she has come to a stop but it starts right back up. It only happens later in the day when it is hot outside, never in the mornings or evenings. I have driven it a number of times to try and get it to happen to no avail. She called the other day and said it wouldn't start so I drove over to where she was thinking that at last I would find something to only discover the car wasn't in park when she tried to start it.

I've read here about the ignition amplifier (power stage) causing this problem but when I discussed it with a Volvo tech he disagreed saying that when they failed they failed outright and not intermittently.

I was wondering what y'all thought and if anyone had this problem and replaced the ignition amplifier (power stage) and not have it fix the issue?

It's hard to find the problem when I can't get it to act up for me.

I have ordered a power stage along with a radio noise suppression/auxiliary cooling fan relay,fuel pump relay, crank position sensor after reading Dave Barton's site just to have on hand as well as some other items that I found she needed while looking for the problem. I think I'm going to order an igniton switch as well to have on hand.

[Texas240]

Sounds like mine.. Ive been told its the Fuel Pump Relay. I'll replacing mine today

[shoesr4fools]

Sounds very similar to when I had the crank sensor go on my 740. Cheak the sheathing on the wire leading to the sensor and if it's cracked and you can see the yellow insulation it's time to replace

[smokeyfan1000]

I would suggest checking and cleaning the fusebox contacts/fuses first. Amazing what a little white corrossion on the fuses/fusebox contacts can cause (just found it causing intermittant radio play on my 91 240)

BUT...Not a bad idea to replace the CPS just from/as "a preventive maintenace standpoint", but replacing the Fuel Pump Relay is a good preventitive maintenance also.

How long since the main fuel pump's fuel filter has been replaced? I've had a clogged/very dirty FF cause rough running/seemingly cut off/on, intermittantly before.

Also, what is the level in the fuel tank when this occurs? half tan or less? never does it when tank is full- 3/4? Has it cut off, then crank right back up in around 2-5 minutes and run fine for 15 miles or so & repeat the 'problem"? This is usually a sign of the in tank pump failing.

[just dave]

Thanks for the replies.

The condition happens regardless of fuel level and it seems to be electrical and outside temperature related based on her description.

[2manyturbos]

The Volvo tech is absolutely wrong about the ignition amplifiers. My top choices in order would be: CPS, fuel pump relay, ignition amplifier, radio supression relay. The RSR is not known for causing the car to suddenly shut off. A bad CPS is definitely known for doing that. So are the ignition amp and the fuel pump relay.

[just dave]

Originally Posted by 2manyturbos

The Volvo tech is absolutely wrong about the ignition amplifiers. My top choices in order would be: CPS, fuel pump relay, ignition amplifier, radio supression relay. The RSR is not known for causing the car to suddenly shut off. A bad CPS is definitely known for doing that. So are the ignition amp and the fuel pump relay.

I figured he was after seeing so many people with similar problems being fixed with an ignition amplifier. I ordered the CPS, Fuel pump relay,Ignition amplifier, and RSR just to have them on hand because the seemed like common failure items with maybe the RSR being the exception. I got it because it is also the same relay used by the auxiliary cooling fan which I'm also replacing because it is not working. I really would like to get a hold of a engine harness in good condition,God knows I don't want to have to resort to making one.

I got the parts you sent,thanks again and thanks for the reply.

[peehound]

I've had both the fuel pump and the power stage do that.

[BDKR]

Originally Posted by 2manyturbos

The Volvo tech is absolutely wrong about the ignition amplifiers. My top choices in order would be: CPS, fuel pump relay, ignition amplifier, radio supression relay. The RSR is not known for causing the car to suddenly shut off. A bad CPS is definitely known for doing that. So are the ignition amp and the fuel pump relay.

Having a '91, does he have a radio suppression relay? I thought that was a 2.2 thing? Or is it a 240 thing? I've had nothing but 2.4 240's and 2.2 700's.

For the OP: Check loose grounds. I had an issue like that. It was positively ghostly! Very difficult to pin down. After replacing things which I planned on replacing anyway (just on an accelerated schedule), I stumbled on to the issue by accident.

[Texas240]

does your fuel pump relay get hot?

[just dave]

Originally Posted by Texas240

does your fuel pump relay get hot?

I have not checked. I'll check that when I get some time. I did notice the sheathing of the wires to the CPS is cracked and copper is exposed but I'm hesitant to mess around with it until the replacement shows based on the condition of other connectors on the engine harness.

[smokeyfan1000]

Originally Posted by just dave

I have not checked. I'll check that when I get some time. I did notice the sheathing of the wires to the CPS is cracked and copper is exposed but I'm hesitant to mess around with it until the replacement shows based on the condition of other connectors on the engine harness.

Sounds like part of the problem there. Is MEWH in good shape? How do the FPR wires look? Burnt?

[just dave]

Originally Posted by smokeyfan1000

Sounds like part of the problem there. Is MEWH in good shape? How do the FPR wires look? Burnt?

The problem I've seen so far with the MEWH is that whatever is used to lock the terminals in the connectors (looks like it was some type of rubber boot/sleeve)had degrade to the point that when I've disconnected some (only a couple so far) connectors the connector slides down the wire and the terminals stay attached.

Have not looked at the fuel pump relay yet with regards to checking to see if it get's hot or checking the connection it plugs into or the wires coming from that connection which I assume is what you are asking.

[smokeyfan1000]

Most 90s volvos still seem to have MEWH in decent shape.

But if it is bad, the problem will usually be found inside the sheathing where MEWH goes under the aluminum frt timing cover, right at the leading edge of the oil pan.

The years upon years of the engine oil's heat bakes it pretty good here, and often you'll find the wires inside with no insulation left on them in this area, , due to the fact it just fell off.

Then the naked wires will touch, sometimes continously, and sometimes intermittantly, causing dead shorts, and all types of electrical problems.
Usually, in my experiences, the 1st system is no output from the alt.

And very quick failure of a new alt after you install one. Usually anywhere from instantly to one week. Just a matter of when the alt wires short out & blow the alt.

[turbopop23]

When my 92 740 turbo did this it turned out to be a faulty crank position sensor. Replaced it and the problem went away.

[volvo_dave]

same exact symptoms as my bad crank sensor

[just dave]

My wife reports that it has stopped acting up since I looked at the wiring on CPS. I guess I moved it enough to keep it from acting up. The new one is on its way.

Thanks again all.

[Lando]

Originally Posted by just dave

My wife reports that it has stopped acting up since I looked at the wiring on CPS. I guess I moved it enough to keep it from acting up. The new one is on its way.

Thanks again all.

Your going to have to repair that section of wire or replace the harness if you want your wife to have a reliable car. Replacing the Cps is pointless if the wiring to it is faulty. Kinda like using a nice locking carabiner while rapelling with twine.

[2manyturbos]

Originally Posted by BDKR

Having a '91, does he have a radio suppression relay? I thought that was a 2.2 thing? Or is it a 240 thing? I've had nothing but 2.4 240's and 2.2 700's.

For the OP: Check loose grounds. I had an issue like that. It was positively ghostly! Very difficult to pin down. After replacing things which I planned on replacing anyway (just on an accelerated schedule), I stumbled on to the issue by accident.

All the 7/9 series turbo models have the radio suppression relay.

[just dave]

Originally Posted by Lando

Your going to have to repair that section of wire or replace the harness if you want your wife to have a reliable car. Replacing the Cps is pointless if the wiring to it is faulty. Kinda like using a nice locking carabiner while rapelling with twine.

I'm going to throw that section out with the CPS. It's damaged right where the wires go into the sensor.

[Lando]

Originally Posted by just dave

I'm going to throw that section out with the CPS. It's damaged right where the wires go into the sensor.

Ok that makes more sense now. I guess I was incorrect to assume that were were as dumb as a bag of dildos. I just cant read.

[just dave]

Originally Posted by Lando

Ok that makes more sense now. I guess I was incorrect to assume that were were as dumb as a bag of dildos. I just cant read.

Time will tell. Who knows? I may be dumber.

[just dave]

Well I installed the new CPS as well as a fuel pump relay, and radio noise suppression relay for good measure but in typical fashion the car has not acted up since I moved the CPS harness. The CPS did have a pink/purple substance that looked like it had oozed out of it right were the wires enter the CPS. I don't know if that was some kind of potting compound or something someone else put on it.