fasteddyT5 Posted August 31, 2016 Report Share Posted August 31, 2016 Hi, I have lately been dealing with an intermittent stalling issue and have had little success in diagnosing and fixing the problem. The car tends to run well on the first trip of the day, but after its sits hot for a bit the rpm's will stumble occasionally and some times this lead to a stall. Usually the car refires right away, but sometimes it takes a few tries. On these occasions is seems like the car fires but doesn't stay running. After trying a few times it will finally keep running. The issue began when I damaged to plug wires for the cam position sensor, but the sensor has been replaced and I did not see any apparent damage on the car side of the sensor plug. The car always cold starts without issue. The stalling issue most commonly occurs at idle or with the clutch disengaged (effectively at idle then), but also occurs when the clutch is engaged and throttle is being applied (i.e. regular driving). Overall it feels like a fuel issue, either from it being cut off by the computer or some other part of the fuel delivery system not functioning properly. The car is a 1998 S70 T5M with 202k miles on it. I drove the car cross country at about 188k miles so in preparation for this trip a number of maintenance items were replaced. Spark plugs were replaced at 169k and plug wires at 109k (with Bougicord wires), cap and rotor at 187k. The fuel filter was replaced at 188k. All the vacuum lines have been replace with silicone and there is no sign of a vacuum leak. Other than the occasional stall or stumble, which happens on maybe 5-10% of my trips the car is running great and pulls very strongly. Fortunately I have a cheap local pick n pull yard near me so I have been working through the likely components. I have been going through the ignition system one part at a time to try and diagnosis the problem. I have replaced the cam position sensor so the car is starting from cold just fine. So far I have cleaned the MAF (I am waiting on a known working replacement from my brother, these do not seem to last long in the salvage yard) and cleaned the idle air control. I have swapped out the coil and coil wire, fuel pump relay, in tank fuel pump, coolant temp senor. I also swapped in a spare 1998 T5M ECU (I am planning to sell the car soon so if anyone is interested in the ECU send me a PM to make an offer, it will get listed on the classifieds some time soon). So far nothing has seemed to affect the stalling issue. Also I regapped my spark plugs (which are volvo oems) to 0.028. One plug did seem to be worn a bit than the others, but is now properly gapped. I am planning to swap out the MAF once I get my hands on one and the 02 sensor (once I can get mine freed up). The only codes I have received are a high voltage code on the front 02. This occurred once early on when this started happening but has not reappeared in several weeks. Twice I received a MAF code (I forget which one at the moment). These codes were thrown only after the car had already stalled and was having difficulty restarting. There have been no codes thrown during driving or when the car refires in less than 2 or 3 tries. I could see the spark plugs being a potential problem at idle but I wouldn't think that they should cause a problem when the engine is under load, and I would expect that this should throw a misfire code. Is there anything I am missing? I am open to all suggestions as to what to check. The issue seems to happen to intermittently to be easily diagnosised at a shop and they likely would want to throw new parts at to work through the systems. Link to comment Share on other sites More sharing options...
Fudge_Brownie Posted August 31, 2016 Report Share Posted August 31, 2016 Sounds like a MAF or O2 sensor problem, giving bad info to the car. Does this only happen when the car is warmed up? My gut says O2 sensor issue, but that's mostly influenced by a recent problem of my own. Any pending codes? Link to comment Share on other sites More sharing options...
fasteddyT5 Posted August 31, 2016 Author Report Share Posted August 31, 2016 Yes, it principally happens only when the car is warmed up, usually after I have made one trip, let the car sit for a bit and then drive it again. I have soaked the 02 sensor a few times with penetrating oil. It wasn't to move in the past. The exhaust is original so I haven't wanted to put too much stress on trying to get it loose. The front o2 was changed out at 115k miles, back in 2007, so it won't be surprising that it is ready to be replaced again. Link to comment Share on other sites More sharing options...
gdog Posted August 31, 2016 Report Share Posted August 31, 2016 Since it's not setting a misfire code I doubt it's the ignition system.. and BTW; ignition is more likely to misfire under load than at idle..FYI 2 hours ago, fasteddyT5 said: I could see the spark plugs being a potential problem at idle but I wouldn't think that they should cause a problem when the engine is under load, The symptoms really sound like fuel pump relay and/or the fuel pump, but you said those were replaced; with known good parts? May need to drive around w/fuel pressure gauge attached for awhile to rule that out.. Have you checked your fuel pressure? Link to comment Share on other sites More sharing options...
fasteddyT5 Posted September 1, 2016 Author Report Share Posted September 1, 2016 I have not checked the fuel pressure yet, but that is something I had been thinking I should do. The fuel pump relay and pump that I swapped in are from a salvage yard so I do know there condition. My thought though was that it seems unlikely that if the are functioning but faulty that they would exhibit the same failure symptoms as the current parts. When I put the used fuel parts in there was no change in the how or when the car is stalling. I had a similar thoughts about the ignition system, but the car seems to stall or stumble at both idle and under load. Link to comment Share on other sites More sharing options...
Fudge_Brownie Posted September 1, 2016 Report Share Posted September 1, 2016 You can use a piece of wire in place of the relay to test if the problem goes away. Link to comment Share on other sites More sharing options...
hootie6828 Posted September 1, 2016 Report Share Posted September 1, 2016 I think i'd start by looking at the ect sensor or maf. It could an o2 sensor too, but they dont fail nearly as often as people think they do. Do you have the ability to look at parameters with your scanner? Link to comment Share on other sites More sharing options...
fasteddyT5 Posted September 7, 2016 Author Report Share Posted September 7, 2016 I final got my hands on working MAF and that seemed to do the trick. It was interesting, when I swapped the MAF out at first I though that maybe the MAF was bad since it ran rough for the first 5 - 10 seconds, but the it smoothed out and idled nicely. I would guess that this was caused by the old MAF sending bad data to the ECU and it using that to make a fuel map based on this bad data. So when it saw the new MAF readings it was applying its old fuel map at first, but quickly adjusted the fuel flow to the new sensor. I've driven the car around for a couple of days with no issues, so hopefully the issue is solved and I can but back my original parts that I swapped out to test with. Link to comment Share on other sites More sharing options...
atefitty Posted October 7, 2016 Report Share Posted October 7, 2016 On 9/1/2016 at 3:34 PM, hootie6828 said: I think i'd start by looking at the ect sensor or maf. It could an o2 sensor too, but they dont fail nearly as often as people think they do. Do you have the ability to look at parameters with your scanner? I would go with ect...its one of your main fuel controls Link to comment Share on other sites More sharing options...
Fudge_Brownie Posted October 7, 2016 Report Share Posted October 7, 2016 1 hour ago, atefitty said: I would go with ect...its one of your main fuel controls If the ECT signals that the coolant is lower than 'fully warmed up', this causes the ECU to run richer, and is often the cause of gas mileage problems. But I can't think of how it would cause a stall. The car won't start with the ECT sensor unplugged. I'm not sure if it'll kill the car if unplugged while running, or if it just prevents starting. Aside from just straight loosing connection, I don't know that an incorrect temp reading is going to cause stalling. I experienced a slightly similar problem to OP, where the car stuttered/stumbled, no throttle response, and occasionally died just as the car came up to operating temperature. The trick was to put your foot to the floor, causing the ECU to ignore the O2 data, and it would suddenly snap back alive. Once the car warmed up, the problem wasn't present. At first, I don't think it gave any codes, then rarely an O2 code. Eventually the O2 code would set consistently. My O2 was seized in tight, with a rusty hex base, so it took me a while to get around to fixing it but it took care of the problem. Lots of heat from a yellow-can MAPP gas torch. Link to comment Share on other sites More sharing options...
atefitty Posted October 7, 2016 Report Share Posted October 7, 2016 I see this is an old post now and the guy probably has figured it out by now. If a vehicle is running to rich to the point where black smoke is coming out of exhaust it will run like crap and likely stall. The guy needs to monitor his O2 sensor and see if it is running rich if he has the capability and knowledge to do so. From my experience a bad maf or o2 sensor will set codes. He mentioned he had a maf code so I feel he should of went with that. Link to comment Share on other sites More sharing options...
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