740T bucking when cold

That's certainly a fear, new pumps are $$$ and used ones are questionable. I have no idea how many miles are on the pumps, the car has 273K, no way of knowing if either fuel pump has ever been replaced.

Maximum Auto Parts sells a noname set, in-tank and external, for under $150. Worth trying to test for pressure and current draw if you have those specs. If not, IMHO it's money well spent even if the problem is elsewhere.

No way I'm gonna use a noname set of fuel pumps, that part is too critical and I've had too many problems with junk aftermarket parts, I never buy them anymore unless I have no choice, the exception being upgrade components and consumables.

It also doesn't really sound like fuel supply trouble, which should be much worse when the throttle is opened than anywhere around idle. Still sounds like AMM to me. Does it happen reliably enough when cold and not happen reliably enough when warm that you can lay a hot water bottle on the AMM and connector before starting to see what that does?

Mike

I just thought I would clean my idle mixture set up ,got some small grit out and discoloured oil ,as well cleaned the contacts on the oxy sensor as well .I use "start ya bastard"which is an ether based product .Boy did my wife react when she first saw the label on the can ?Works on lawn mowers as well but not on me sadly I am just plain lazy :)

It's only happened four times so far, so not particularly often, I'm hoping it will either go away or start happening all the time so I can find the cause. I cleaned the connector on the AMM and it hasn't done it again yet, but I've only driven the car once since then.

That really makes it sound like something other than fuel pumps themselves, although I suppose the fuel pump relay part for the pre-pump is flaky. Still, that more often shows up as starting trouble then rough running.

Here's hoping the connector cleaning does the job!

Mike

My '84 240 Turbo does not have K-jet, it has CIS with the fuel distributor in the front right hand corner of the engine compartment.

I did resolder the fuel pump relay a couple years ago just for good measure, I'll check that again just to make sure anyway though.

The Volvo manuals show that K-Jetronic injectors are electrical. Mine are not. The pipes from the fuel distributor come directly from the fuel distributor to the intake manifold. The Volvo manual shows no electronic fuel injectors for turbos in 84.

They're wrong then. K-Jet is entirely mechanical aside from the frequency valve which is part of the Lambda-Sond system present on "newer" cars.

LH-Jet is the system with electrical injectors.

I missed the earlier replies - was there a diagnosis of the bucking problem? My 1994 940 Turbo wagon (US specs) has developed it for a few minutes after running fine when completely cold, then runs fine afterward.

The squence is the same now: Start the car and it runs fine for the first few minutes. Then it bucks and revs up and down for several more minutes. Then settles down and drives normally for the rest of the trip.

It seems (from the symptoms) that when the car is completely cold, the appropriate system is working properly for a cold engine. Likewise for the "warm" system when the car is fully warmed up. There is a short period of time, though, between the two when the car "bucks".

I was hoping to find the, or a possible, answer without a trip to the Volvo shop.

Yes, I will search the archives, but wanted to ask the question in case there is more current information.

NCMan

Usually turbo intermittent bucking is due to a fuel delivery problem in the tank, either a separated/rotted fuel feed hose from the prepump or a faulty prepump. Given that all other systems have been checked and found ok.

Bob

Well I had to make a run to the store tonight and as I started coasting down the hill it started bucking again and then stalled. I pulled over and was able to get it to start again but it quickly died. Fiddled with the connector on the AMM and poked around under the hood a bit, started and it was idling but as soon as I tried to ride out the clutch the car started lurching and bucking, though I could rev the engine ok with the clutch in. I finally got it running a little better and managed to nurse it back up the hill into the driveway at which point it naturally started idling fine.

Popped the hood and started poking around with the engine running and found that if I poked at the wire on the #2 injector the engine died instantly. Did that twice, then pulled the connector off, looked fine so I stuck it back on. Now no amount of poking or tugging has any effect, even unplugging the injector with the engine running doesn't make it run nearly as bad as it was on the road. My first thought was wires deteriorating under the outer sheath but squishing and rolling around the wire now has no effect. By this time it's after midnight so I can't be out there screwing with it much but hopefully I can track this down for sure. I'm thinking new wiring harness is the best next step but christmas pretty well took care of the budget this month. Maybe I can patch up the existing one until I can find a recently replaced harness at the wrecker.

Good ideas. I will look into them in the morning.

NCMan