Engine 850: B5252S/2.4/10v: Missing/Hesitation Under Load (again, ideas?)

[DmcL]

all i see that looks remotely similar to anything i have seen t odo with the air pump is the fan relay above the radiator. theres definately nothing looking like the air pump i have seen anywhere on or around the front of the engine.

[Chris_Rogers]

The launch is c**p on Volvo and not much good on any thing else.

Make a DIY LED code reader:

http://www.volvoforums.org.uk/showthread.php?t=46943

or buy one from Jod.

An air pump looks like this:

http://volvospeed.com/Repair/airpump1.php

[DmcL]

i definately dont have a pump then. the hose from the airbox on my 10v goes to the ICV and then into the intake elbow. also have nothing resembling that SAS valve in the back of the engine.

makes me wonder what that code 4-4-2 really is then?

[Chris_Rogers]

Well the simple way is to make the reader and read the correct code. This may help diagnose your problem.

[DmcL]

disconnected the battery for a while and re-connected it then took the car a run. no engine light yet but the hesitation/missing is happening from cold this time tho still not as bad as previously where the car was undrivable. it will hesitate/mis in 1st gear if i try to move off quick-ish and slip the clutch out at about 1.5-2k rpms. the hesitation generally doesnt happen on full throttle if i were to rev all gears high but if i get on it from even the mid rpm's in 2nd, 3rd, 4th, 5th it will hesitate and mis.

i pressed all plug leads onto the dizzy cap to ensure they are on good, same for the coil, also moved where the lead from coil to dizzy runs and moved crank position sensor wire back and down more but no good.

next thing im going to check is the plugs, they havent even covered 100 miles so if they are covered in deposits then i know somethings up. no abnormal smoke from the exhaust or anything. there is some oil running thru the drip passage between the rocker cover and sparkplug cover but as far as i can tell thats normal on these cars/engines. if the plugs look covered/fouled enough to possibly cause the hesitation/missing then ill clean them and see if it stops the problem.. if so then i guess its time try and flush out the breather passages in the block as the piston bored looked fine when i had the head off and the head was skimmed and vacuum tested for leaks so im pretty sure i can rule out the top and bottom end (breather might explain the oil passing out the top and thru the drip passage in the rocker cover).

failing that could be a sensor on its way out i guess.. have to wait and see if the engine light comes on and what code/s its throwing.

at idle i could hear the ignition coil ticking away with a uniformed sort of constant rhythm. couldnt really hear when i gave the engine a slight rev via the cable reel/tb but far as i can tell the coil seems to be fine.

[DmcL]

just poking around looking at generally what sensors give what problems when they start to go or fail completely. doubt its TPS related.. dont even know if this will work with my 850 or not but i figure for the sake of trying i may as well.

In all cases a manual recalibration of the TPS may resolve the issues at least on a temporary basis. To recalibrate the TPS: -

1. With the engine off, insert the key and turn the ignition to position 2 (On) without starting the engine.
2. For MEMS-equipped cars (S1), quickly press and release the accelerator pedal several times (at least 5, but to be sure 8 or 9) using as much of the throttle travel as practicable. This will trigger the ECU into the closed-throttle reference learn algorithm, which has it looking for the lowest measured static throttle position (the closed position). The throttle position calibration is a fixed definition from this point.
3. Turn the ignition off, remove the key and wait for the ECU to power down (about 30-40s).
4. Start car as normal.

[testrider]

Just picked up on something said earlier about code readers. My 850 was a '95 with the 2.5 10 valve and the Fenix engine management has a built in code reader next to the washer bottle filler. There's a little lead that you plug in and then an LED flashes the codes to you. Not sure if it's the same on your '97 model but it's quite handy if you find it.

[DmcL]

i read about that before but as far as i can tell mine doesnt have it.

[kevin derby uk]

Originally Posted by DmcL

in allthe work that i have done to the car (head off, changed coolant hoses, changed oil and filter, etc..) i havent seen anything remotely resembling the air pump that i have seem pics of on the net. where exactly is the pump located?

the code i was getting was 4-4-2 "air pump relay int. fault" tho the code reader that was used didnt read the codes straight away when volvo 850, year 1997 and engine was selected.. ended up having to try other volvo ones on the diagnostics computer and if memmory serves we only managed to get the code up either under a different model or under the search/automatic selection type mode on the computer.

this is the reader we used.. also will be this reader we try to pull the codes with this friday. managed to erase the 4-4-2 but the light came back on about 2 weeks later, assuming its for the same code.

its a Launch X-431

dont suppose anyone has had any experience with one of these? seems like it should be top notch stuff going by the price tag (a mere £2000 lol)

iv got the use of one but need to know which adapter to use as the one i used blew so c e m fuses. the cars a volvo s80 2003. any help thanks

[DmcL]

dunno lad.. i never used it just watched.

regarding my hesitation/missing i did some reading on the EFI system and a MAP sensor equipped system isnt affected nearly as much as a MAF equipped system by vacuum leaks. im doubting a vacuum leak is the cause anyway..

now i also learned how MAP based systems work. they use the MAP sensor, TPS, sometimes lambda, RPM signal and intake air temp to estimate airflow and calculate fuelling accordingly.

so armed with that knowledge i idled, revved and drove the car around the carpark at work first as normal with the mis/hesitation then again with the TPS disconnected, hesitation was still there so dont think TPS is an issue. also tried unplugging the ICV but again no affect and doubt thats anything to do with it. i then unplugged the MAP sensor and the hesitation was gone tho idle was up and down then eventually settled anytime i revved or depressed the clutch and allowed the revs to drop. the revs dropped below normal idle and bounced back so im guessing the MAP sensor is functioning but its interesting that the hesitation went away with the MAP sensor unplugged. i disconnected the battery to reset the ECU/EML and drove the car to the GF's house as normal and sure enough the hesitation was back. i disconnected the MAP sensor once again before driving home and again the hesitation was gone.

so im wondering could my MAP sensor be faulty or not functioning fully or properly? i noticed that it is a GM MAP sensor and considering the number of vauxhalls in the local scrappers im going to go and try to hunt one down on the various vauxhalls laying about.. hoping ill get one then i can swap them over and see if it has any effect.

also i pulled all 5 sparkplugs to compare them with one another and all look the same, also WD-40ed inside the plug lead boots and checked all connections onto the distributor and coil, all seem fine and no visible damage to any of the leads so doubt its any of that.