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Car Forum / Volvo Cars / December 2005740T bucking when cold
After years of solid running, in the past few weeks my '87 740 Turbo has had a strange intermittent problem when cold. Either right after it's started or shortly after the engine will suddenly start idling very poorly, RPM dips down to 300-500 RPM and stumbles for several seconds, then it's fine. First time it happened I was pulling out into traffic and the car lost all power, started bucking heavily and sputtering, then suddenly roared to life with a spectacular burnout. The next time I was coasting down my hill when it started stumbling so I pushed in the clutch and coasted for a few moments until it recovered. Once it goes back to normal it runs great for the rest of the day, haven't had any other problems at all. What do you guys think? I'm leaning towards the beginnings of problems with the AMM, I'm afraid I might be chasing my tail trying to track this one down since it happens relatively rarely. It really feels like a fuel problem though. > After years of solid running, in the past few weeks my '87 740 Turbo has > had a strange intermittent problem when cold. Either right after it's [quoted text clipped - 12 lines] > one down since it happens relatively rarely. It really feels like a fuel > problem though. Distributor leads? That's what caused similar probs with mine, specially when it rained. > Distributor leads? That's what caused similar probs with mine, specially > when it rained. I can check them, they're Magnecore wires though and only a couple years old. Hasn't rained lately either. I haven't checked the distributor cap lately though. > After years of solid running, in the past few weeks my '87 740 Turbo has > had a strange intermittent problem when cold. Either right after it's [quoted text clipped - 12 lines] > one down since it happens relatively rarely. It really feels like a fuel > problem though. That is odd. How about the operation of the throttle position switch? Maybe it's getting balky when cold and isn't coming out of idle mode. Listening for the click with the engine off is a good start. But it always could be the AMM/connector. Mike > That is odd. How about the operation of the throttle position switch? Maybe > it's getting balky when cold and isn't coming out of idle mode. Listening [quoted text clipped - 3 lines] > > Mike I hadn't thought of that switch, I think I've eliminated it though as the last time I had this problem I was coasting with the clutch in and the engine was idling very rough and stumbling still, just as it does with more throttle applied, it doesn't seem to make a difference. >> That is odd. How about the operation of the throttle position switch? >> Maybe it's getting balky when cold and isn't coming out of idle mode. [quoted text clipped - 8 lines] > engine was idling very rough and stumbling still, just as it does with > more throttle applied, it doesn't seem to make a difference. Ugh - I'm no expert on that but it does make me think of the AMM. The connector on mine acted up, causing similar symptoms, and with it barely idling I pressed on the connector a bit and the idle jumped up (like starting) and then settled down. Cleaning the connector with alcohol (because that was the best contact cleaner I had around) fixed it right up. Mike > Ugh - I'm no expert on that but it does make me think of the AMM. The > connector on mine acted up, causing similar symptoms, and with it barely > idling I pressed on the connector a bit and the idle jumped up (like > starting) and then settled down. Cleaning the connector with alcohol > (because that was the best contact cleaner I had around) fixed it right up. That had been my original suspicion, I'd just wanted to check if there was anything else likely. I'll try cleaning the connector and see if that helps, if it starts having the problem more regularly it'd be easier to track it down. I do need to figure it out though, it's dangerous, I'm afraid I'll forget and charge out into traffic and end up broadsided when I lose power. Have we determined whether or not the OP has a turbo or not? I know that not all Volvo's with a "T" in the designation have been turbos in the past. I don't think that any Volvo turbos had an MAF sensor. >>>That is odd. How about the operation of the throttle position switch? >>>Maybe it's getting balky when cold and isn't coming out of idle mode. [quoted text clipped - 16 lines] > > Mike > Have we determined whether or not the OP has a turbo or not? I know that > not all Volvo's with a "T" in the designation have been turbos in the > past. I don't think that any Volvo turbos had an MAF sensor. Mine does :-) / :-( Mike > Have we determined whether or not the OP has a turbo or not? I know > that not all Volvo's with a "T" in the designation have been turbos in > the past. I don't think that any Volvo turbos had an MAF sensor. Yes it's a 740 Turbo with a B230FT, hence the T I put in the post, the only Volvos with a T in the designation and no turbo were the GLTs. Only the 240 Turbos had K-jet, the 700 and 900 series all had either LH with the AMM or possibly Regina, not sure whether the turbos got that or not. >> Have we determined whether or not the OP has a turbo or not? I know >> that not all Volvo's with a "T" in the designation have been turbos in [quoted text clipped - 4 lines] > the 240 Turbos had K-jet, the 700 and 900 series all had either LH with > the AMM or possibly Regina, not sure whether the turbos got that or not. 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. >>> Have we determined whether or not the OP has a turbo or not? I know >>> that not all Volvo's with a "T" in the designation have been turbos [quoted text clipped - 8 lines] > 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.E. K-Jet... >>>> Have we determined whether or not the OP has a turbo or not? I know >>>> that not all Volvo's with a "T" in the designation have been turbos [quoted text clipped - 10 lines] > > I.E. K-Jet... 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. > 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. >> The Volvo manuals show that K-Jetronic injectors are electrical. Mine are >> not. The pipes from the fuel distributor come directly from the fuel [quoted text clipped - 5 lines] > > 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 > >> The Volvo manuals show that K-Jetronic injectors are electrical. Mine are > >> not. The pipes from the fuel distributor come directly from the fuel [quoted text clipped - 26 lines] > > 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  SignatureThe goal when driving is to miss the maximum number of objects. >> >> The Volvo manuals show that K-Jetronic injectors are electrical. Mine >> >> are [quoted text clipped - 40 lines] > > Bob Good ideas. I will look into them in the morning. NCMan This is undoubtedly happening just as the engine computer systems are going closed-loop. You undoutedly have one or two timed vacuum switches screwed into the block and/or cylinder head. When the coolant is warming up, these thermostatically timed vacuum switches open to allow vacuum to various other components, one of them being the charcoal canister, turbo overboost switch and in the case of my old '84 Turbo, the distributor advance. It might be time to check ALL of your vacuum lines and replace them. I just replaced all of my lines...took about two weeks and made a HUGE difference. You should have seen the condition of some of them, they were all sucking air. My old Volvo, from the day I drove it from the dealer has had that idle decrease and a bit of rough running during warm-up, particularly on very cold mornings just before the engine goes closed-loop. > After years of solid running, in the past few weeks my '87 740 Turbo has > had a strange intermittent problem when cold. Either right after it's [quoted text clipped - 12 lines] > one down since it happens relatively rarely. It really feels like a fuel > problem though. > This is undoubtedly happening just as the engine computer systems are > going closed-loop. You undoutedly have one or two timed vacuum switches [quoted text clipped - 9 lines] > of rough running during warm-up, particularly on very cold mornings just > before the engine goes closed-loop. It can't be going closed loop *that* quickly, it does warm up fast, but the first time it did it the engine had been running literally no more than 10 seconds and it was below freezing outside. I'd hopped in, put on my belt, started it up, put it in gear and started to back out of the driveway when it started lurching like crazy. The second time it'd been running for maybe 30-40 seconds. Also I'm pretty sure it doesn't have any of that vacuum stuff, my 240T has that, but the 740 is LH-Jet EFI. May be time for a new cap and rotor? Sounds like a problem with the fuel enrichment, possibly the thermo-time switch, injector, or wiring. > Sounds like a problem with the fuel enrichment, possibly the > thermo-time switch, injector, or wiring. There is no thermo time switch that I'm aware of, wiring is a possibility, the original harness is a bit tattered, I suppose I should replace that too. Maybe not. I'm only going by the generic L-Jetronic description, which describes a cold-start valve and a thermo-time switch. These add fuel under the conditions you describe. Or your auxiliary air device, which adds extra air during cold-start conditions, is intermittent. Why replace the harness? You can check the wiring using a VOM and judicious bending and tugging. > Maybe not. I'm only going by the generic L-Jetronic description, which > describes a cold-start valve and a thermo-time switch. These add fuel > under the conditions you describe. Or your auxiliary air device, which > adds extra air during cold-start conditions, is intermittent. I'm not aware of any of that stuff, there's a temperature sensor, I'm not sure if that could cause this problem though? It has a CIS valve to regulate the idle by bypassing the throttle plate, that part seems to be working. > Why replace the harness? You can check the wiring using a VOM and > judicious bending and tugging. Because it's clearly rotting out, there's insulation falling off exposed wires all over the place. I've taped most of them up and haven't had any trouble with them yet in the 5 years or so I've been driving it, but it definitly needs to be replaced. Classic pre-89 Volvo problem. "It has a CIS valve to regulate the idle by bypassing the throttle plate, that part seems to be working." That's the aux air device. It would open fully during cold cranking and gradually close as the engine warmed up, finally remaining open just enough to hold a steady idle. Some people clean them out with carb cleaner when they start to stick. Have you tried cleaning out the slops in the air fuel mixture gizmo under the intake manifold .Try cleaning its electrical connection as well .It gets messy when you use normal oil and needs a good flush out so it can slide in and out to alter the mixture .Its easy to remove and clean .Now your heading for winter ,it might be more sluggish with thicker glug . > After years of solid running, in the past few weeks my '87 740 Turbo has > had a strange intermittent problem when cold. Either right after it's [quoted text clipped - 12 lines] > one down since it happens relatively rarely. It really feels like a fuel > problem though. > Have you tried cleaning out the slops in the air fuel mixture gizmo under > the intake manifold .Try cleaning its electrical connection as well .It gets > messy when you use normal oil and needs a good flush out so it can slide in > and out to alter the mixture .Its easy to remove and clean .Now your heading > for winter ,it might be more sluggish with thicker glug . Air fuel mixture? You mean the idle speed valve? That has nothing to do with mixture, it allows a variable amount of air to bypass the throttle plate to regulate the idle speed. I cleaned it out about a year ago, might be time for it again but I really don't think that's my problem here since I've experienced it both at idle and all the way up through WOT. Once it happens though it seems to not happen again until the engine is very cold. Or possibly a fuel pump problem. > Or possibly a fuel pump problem. 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. > 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. > 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 :) > Have you tried cleaning out the slops in the air fuel mixture gizmo under > the intake manifold .Try cleaning its electrical connection as well .It [quoted text clipped - 18 lines] >> one down since it happens relatively rarely. It really feels like a fuel >> problem though.
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