19 replies to this topic

[Dietmar]

I am getting pretty poor acceleration from the engine in lower rpms (I think around 1500) when flooring the gas pedal (or close to flooring it), in particular (or only?) when the engine is warm. When rpms are up, everything's great. I am not getting a "check engine" light, and I have no error codes stored. Recently, I got the air supply hose replaced - it was leaking between engine and MAF sensor, and we cleaned MAF sensor as well.

What I learned from other posts is that a faulty ECT Sensor can make the engine's computer "think" the engine is still cold when warm, and then it floods the engine with too-rich a mix when flooring the accelerator in lower rpms.

My question: should I just go ahead and replace the ECT Sensor (and the coolant thermostat, while I am at it)? Replacing coolant fluid might be a good idea, as well (last time 2.5 years ago, I think) or is there something else I should do first?

[GP850T]

Replacing the coolant sensor and t-stat is a good idea and relatively cheap, but somehow from what you described i dont think thats your problem..

When you go on the highway does your Temp gauge reading fall? If so then replace the tstat and ect cause thats the problem..

Things that you can do that are cheap and easy, go look over the throttle cable see if it glides properly, you can also clean out the throttle body by removing it all together and spraying it with carb cleaner.. remove the hose running to it and after thats its only 4 bolts, dont forget to detach the spindle. you will need a new tb gasket which is about a dollar..

What did you clean your maf with, they are very sensitive sensors and dont generally require cleaning/

Hope this helps

[Dietmar]

thank you for the reply! I will pay close attention to the temp gauge tomorrow, but I didn't notice anything unusual so far. We had cleaned the maf sensor because there was a stored error code about the maf sensor when we replaced the air supply hose, and the error came back again. (then again, it could have been anything - like they forgot to connect it before starting the engine for the first time after replacing the hose, who knows.) We cleaned it with some electronics cleaner from a spray can that my mechanic had on hand. After that, no more fault codes in that department. I guess I will order that throttle body gasket along with the other parts and take care of that cleaning, as well.

[Dietmar]

Okay, just got back from a trip with the car, some 30 miles each way. Again, no problems with cold engine, but getting off a red light with warmed up engine was awkward. In those situations I typically bring the engine to 2000 rpms and letting the clutch slide (manual transmission, 163k miles) to get to speed in 1st gear, then managing the "hole" in 2nd gear, fewer problems in 3rd & 4th. My wife noticed gasoline smell when getting off from red lights, and I guess, too, it was coming from our car.

Paid attention to what happens when getting on the highway, but I didn't notice any drop in indicated engine temp - the gauge hand remained steady at "3:15" (just below medium temperature.

You are saying that in this case my coolant temp sensor should be fine? Can you explain? Thank you!

[Hanks]

check the cap and rotor. if you have a multimeter check the spark plug wires.
check spark plugs. you may not be getting a good burn causing the fuel smell..
check the timing belt to make sure everything is ok there. you may want to check the TDC and make sure its correct, if not it can cause power loss up top or down low.
check fuel pressure.
reset ECU by unplugging + battery cable
check flame trap. http://volvospeed.co...eplacement.html

Edited by Hanks, 21 February 2011 - 11:15 PM.

[Dietmar]

just spent some time driving the car with my mechanic. Of course, we didn't notice any issue, grr... I will have narrow down the exact conditions a little better. Perhaps the weather has to get a little warmer and the engine has to warm up even more (the temp gauge was at the warm setting pretty soon, whereas I observed the issue only after at least 15min driving.) Mechanic says fuel system should be fine since the car does great at higher rpms. He suggests to give replacing coolant temp sensor and thermostat a go since it's cheap and a good idea anyway, so we'll do that one day soon. Thanks for everyone's input and I'll provide updates to this.

[Dietmar]

just a quick update: Replaced engine coolant sensor (and also thermostat) last week. Done little driving, but so far no issues. I was partly prompted to swift action because I had to replace the electronic climate control board: it went up in smoke. The replacement worked, but it showed error "135 - no signal from engine coolant temperature sensor". So I thought: gotcha. However, the error keeps coming back. Seems like the ecc throws the error every time I leave the ignition in the I position (for radio or so). No ignition, but ecc powered, so it fails on the engine coolant sensor.

I don't know anymore whether the old ecc showed the 135 error, as well. Might be irrelevant: when I checked those codes, the ecc was already burned up and issued all kinds of error, it was a different part number than the new one, and if the problem is mereley a result of leaving the key in position I it wouldn't matter anyway.

Either way a good thing I did this work: upon removal, the old thermostat fell apart...

[jablackburn]

Try cleaning up the plug to the coolant temp sensor. Someone just last week had gone through replacing tons of things only to discover that the plug was corroded and giving a bad reading.

[Dietmar]

This topic deserves an update. I didn't do anything about the issue since replacing the coolant temperature sensor and the thermostat, and the car appeared to be driving fine. Until a few weeks ago, when it started to sputter during (attempted) hard accelerations. I researched it and the cheapest way to trouble-shoot appeared to be to add a fuel system cleaner and replace the fuel filter. I have been driving the car for perhaps 100 miles with a bottle of Red Line 60103 SI-1 Fuel System Cleaner - 15 oz in it, and the issues are gone and the car is driving very well again with full power back at acceleration. I got the new fuel filter but keep it in the trunk for the next garage stop - I leave that to the experts. My guess is that the fuel system had never been cleaned, nor had the filter been replaced. For $10 and no work/wait, this seems almost to easy a fix

[Vagabond]

Dietmar, on 21 June 2011 - 02:12 PM, said:

... I got the new fuel filter but keep it in the trunk for the next garage stop - I leave that to the experts.

Left loosey, righty tighty.

If you can follow that logic as well as Pull off and Put on a small rubber hose, then you sir, ARE a Fuel Filter Expert.

Swap that thing out Asap. Fuel System Cleaner is going to make that junk in the filter disappear.

[Dietmar]

Hi all - I am back. Still working on that acceleration problem. It has gotten colder, and I am now experiencing irregular power output with steady gas when accelerating with warm engine, maybe less so with a cold engine, but I am not certain. Cruising is fine, but uphill or accelerating the output randomly drops to like 50% and then back to 100% (I guess - perhaps it should do even better with pedal near the floor). Also: In late summer, the car stalled three times at red lights or when parking with warm engine. So the matter had been entertaining.

What we have done: replaced the fuel pump (I don't think it changed a thing). Cleaned throttle body (minimal deposits reported) and replaced the gasket. Discovered leak in exhaust manifold, explaining the fume smell when standing. Already reported: replaced engine coolant temp sensor. Replaced fuel filter.

So far the only thing that appeared to have made a difference was the $10 fuel system cleaner, but I don't buy that not using that for 1000 miles or so will make such a difference. Just to see, I had disconnected the MAF sensor - I read some place that if that is giving bad data the car should run better without it being connected. Well, it ran really poorly without it.

Leaving out tossing in more fuel system cleaner, what's a good idea here? Try a different MAF sensor (would love to try without buying...)?

Here's Hank's list from his 2/21/2011 post in this thread:
>check the cap and rotor. if you have a multimeter check the spark plug wires.
>check spark plugs. you may not be getting a good burn causing the fuel smell..
>check the timing belt to make sure everything is ok there. you may want to check the TDC and make sure its correct, if not it can cause power loss up top or down low.
>check fuel pressure.
>reset ECU by unplugging + battery cable

I am not sure whether all this has been done by the mechanic. I can bug him again about this list on my next visit but would love to hear more suggestions. Thank you!

[Dietmar]

So it happened again tonight: warm engine, waiting at red light, engine sputtered and died. Didn't restart right away. Waited a 20 seconds or so and then it started without hesitation. At destination, I tried it: started engine without pressing the accelerator and let it run, then off and tried again. Either it ran fine for minutes or it dropped to like 200rpm and fighting it there for a two or three seconds before finally dying. About 3 out of 4 or 5 attempts were fine, the rest sputtering and dying. Could this be my ECU giving up?

One more thing, in case anyone is wondering: I am familiar with reading the fault codes and everything is clean right now.

[Dietmar]

I am going to check on this airbox thermostat matter tomorrow or so for sure:
http://www.___.com/f...opic.php?t=8830
curious...

that was matthews volvo site

[Bah]

Check out the fuel pump relay. If you haven't replaced it, it's gone or on its way. That was the very first big stall item on my 93, and pretty much all 850's.
After that, i noticed the vacuum line to my fuel pressure regulator had been disconnected for some while. Turns out, this is why i would sometimes stall out at traffic lights if i went slow or sat too long. Had the exact issue, where i started the car with friends in it, went to take a right turn and stalled in the middle of the road. Of course, this was back when the fuel pressure regulator didn't have the vacuum attached, since i fixed that it never stalled again. On your 93 its right there on the fuel rail and you should see the line. make sure its not cracked and is holding vacuum to the tree. Mine fell off pretty easy so make sue its on good. Check the car all together for vacuum leaks. Note, i never got a code saying i had a vac leak, just still have the O2 sensor code.
I found cleaning the flametrap (remove the plastic piece) helped alot, being that my pcv system was old on the car. Lots of oil and gunk in it. Clean that, give the IAC a little clean up too while your at it.
I changed wires a while back too when i fixed the vacuum leak, so i suppose that was possible too. But before the T-belt exploded, it did not stall, only issue was a sorta crummy idle due to VVIS sucking

[Gilhuly]

It would be good to have a known working MAF to swap in. I would be putting my money on a MAF or a FP relay.

[Dietmar]

Great, thank you for these suggestions! I think I will try the maf sensor last, as it is certainly not dead, and I never got fault codes for it. Will check on Bah's suggestions first.

While the airbox thermostat was shot, arresting the airbox to always pull air from the front didn't make much of a difference, if any at all. While playing around with the airbox while engine was idling, I noticed that blocking the airflow with a few fingers already made the engine stall out, and I was only starting to notice the airflow. It was worse with warm engine (stalling with covering 90% of the opening in the airbox, without the filter), less so with colder engine (needed to cover 95%, certainly noticing the draft). Tried driving without filter. didn't stall, but acceleration issues remained. (also tried pulling off the air tube behind the maf sensor - caused engine to die immediately. another test to see that the maf sensor is doing something)

Is the engine in idle so sensitive to air blockage or is this really a sign for something else?

[Dietmar]

update: fuel pump relay ordered. we'll see then.

[Dietmar]

update: fuel pump relay arrived, installed it and had a chance to drive four miles. So far it feels great and I consider this case closed unless I report again. There was some softness in response once on that drive (in the city, so plenty of acceleration action), but overall I dare to say the car was feeling more powerful overall and quite steady in producing the power I called for.

How I would troubleshoot it the next time: For sure check the fault codes and replace the fuel filter. For good measure, disconnect the MAF sensor and see whether the car runs just as bad (bad maf sensor) or worse (maf sensor probably just fine). Also check on the thermostat in the air box and possibly fix it in the "cold air" position. And check for all vacuum leaks, of course, and clean the thottle body. Before replacing any parts on the fuel system, I would next short the fuel pump relay (my car is one of the earliest models with a fuel return line - I've heard that later models shouldn't be shorted on at the fuel pump relay). If that fixes the issue, replace the fuel pump relay. Last option, because it is more involved and the part is more expensive, replace the fuel pump. Mine apparently was still good and I'd say I waisted $200 on parts and labor, plus the inconvenience of having the car at the mechanic. (Now I know I probably could have done it myself - don't have your tank full.)

Thanks again to Bah, Gilhuly and GP850T for contributing!

[Dietmar]

Just discussed this case with my mechanic. He claims that the effort and expense of replacing the fuel pump was not entirely wasted as the old pump might have developed a higher current draw due to higher mechanical resistance and that this could have caused the fuel pump relay to fail. If he is right (we will never know) then first replacing the fuel pump was the right decision.

[Keaton85]

Doesn't matter if there was a higher draw on the relay, as it's a relay! it only activates a armature and the circuit is unaffected by how much current draw is going through it. The fuse will blow WAY before putting to much straight on a relay.

The relay can be taken apart and you can see if it's good or bad by the circuits on the board. They either have bad solder joints or the capacitors will bloat.

Sorry, but the fuel pump "draw" did not take out the relay.