I have a 89 240dl wagon, 168000 miles, i've been fighting a issue with it wanting to "bog down" when I give it gas. It clears up after a second or two and operates properly after that. So if i'm sitting at a redlight at a normal idle its fine, I take off and wants to hesitate ( like its flooding or starving for fuel/air ) then clears up and goes on about its way. has backfired 3 times, only when trying to accelerate hard. I have checked for vacuum leaks with carb cleaner, have one small exhaust leak.

NEW PARTS INCLUDE
: idle are valve
: tps (installed properly)
: injectors
: fuel pumps (both) and strainer/filter
: mass air flow
: pressure regulator
: coil, plugs, wire, cap, and rotor
all have less than 10,000 miles on them
open to all opinions

 

i had symptoms like that on a mercedes, turned out to be the injector seals were letting air in

 

I thought about that before, but when I checked for vacuum leaks I checked them out also, every thing seems to be in working order, im starting to wander if my fuel pump is failing already, I went with a cheaper one due to the price on them.

 

fuel pressure test will tell you if the pumps are working.

a fuel pump failing to deliver /enough/ fuel (clogged filter for instance) will bog down at higher RPMs under heavy throttle, not off the line.

 

My guess is - if the timing is correct, then a backfire is usually too much unburnt gas. Lean engines(again with proper timing) don't backfire - there's nothing to explode. Check the Hall sensor in the distributor, if it has one? Sounds like a spark issue.

 

1989 is LH 2.4, no hall sensor, timing is by computer (ICU), and the timing source is the crank position sensor, which has no adjustments.

 

I had a similar issue with a 92 740 and it was the fuel pump (Regina). But since you have replaced everything inc, the pumps, not sure. Of course, there always is the possibility that a new part is defective or just bad quality...

 

Have you checked your engine codes? If you have a vacuum leak it more than likely will throw a code.

 

Then it could be the cps. When mine was going out it had very erratic revving.

 

How would a bad fuel pump, which reduces fuel flow, promote backfiring? I think that's the key to diagnosing this. Extra, unburnt fuel explodes in the exhaust system. A bad pump won't provide extra fuel. Gotta be spark related - either due to worn parts or off timing.

When it's misbehaving, pull the plugs - what color are they? Are they wet?, etc

 

Try unplugging your mass airflow sensor and see if it still bogs down like that. I used to sell a ton of those 240s when they were newer and they are pretty foolproof in design and systems.

The fact that the car runs fine once you get over the bog tells me that it probably isn't fuel related but computer related.

 

(don't plug/unplug the MAF when the ignition is on. shut the car off, unplug it, try starting it. it will run in 'limp mode' with slow acceleration and general lack of throttle response but it should run reasonably smoothly. then shut it off, plug it back in, start it again...)

 

im thinking it is a air or a spark problem

MORE INFO=== in my shop I can smell the unburn fuel in my exhaust. now this ( lag or hesitation ) isn't when I first start the car, runs fine for about 8-10 min. once at normal operating temp then it wants to star with the issue

THANKS FOR EVERY ONES HELP
LETS KEEP IT GOING

 

if the coolant temp sensor isn't working (bad wiring, or bad sensor), its quite possible the ECU and ICU think the engine is still cold, and will keep running it rich.

note the dashboard temperature gauge uses a different sensor so even though that one is working, it means nothing here.

 

OK I'll look into swapping that out, any idea on location on the B230F??

Also I will be checking out every thing to do with the ignition on it today

 

The MAF is brand new, less than 100 miles on it. but ill check into it

 

the coolant temp sensor is one of 3 sensors screwed into the head under the intake manifold, the other two are the coolant GAUGE sensor, and the anti-knock sensor.

the anti-knock sensor is flat, and has the wires coming off the side. the coolant gauge sensor has one pin. the coolant temp sensor has 2 pins, one goes to the ECU and the other to the ICU.

 

ok guys, changed the temp sensor, without any luck
I started my car and let get to temp. took off without a problem, but after about 1 mile of driving it started acting up again. so now im thinking egr??
does any one have any info on the egr system?
the only thing I know about it is the "flame trap" and I clean it every other oil change. was cleaned about 3 weeks ago. less than a hundred miles.
any more info on the egr system would help me out a tremendous amount

 

there's a pretty easy test of the EGR system...

first, there's several parts to it. there's an egr vacuum control just forward of the lefthand suspension tower, kinda looks like a 'hat' with two vacuum lines and an electrical connection. one vacuum line comes from vacuum fittings on the intake manifold, the other one goes to the EGR actuator under the intake manifold. the EGR actuator has a pushrod that opens/closes the actual EGR valve, whihc is farther back under the intake manifold.

at the EGR vacuum control, disconnect the vacuum hose that goes to the actuator... connect this vacuum line to a 'mityvac' hand vacuum pump. start the engine, let it idle, suck a bit of pressure on the mityvac, the engine should immediately stumble/stall, release that pressure and it should catch back up and resume idling. if that doesn't happen, but the vacuum pressure holds OK, then odds are, the EGR pipe from the exhaust to the EGR valve is plugged up... this won't effect running, but it can prevent a smog check from passing.

the second test involves the diagnostic block... on pin 6, there's a special diagnostic mode that causes the engine to cycle each of its actuators in sequence, one of which is the EGR vacuum control... so you hook a short piece of vacuum line up to the same nipple you removed the hose that went to the actuator, and gently blow into this hose during that EGR cycle test, you should feel your breathe 'pulse' with the clicking, on/off/on/off. if that works, (and the other test passed) then your EGR should be AOK.

for this diag tests, see step 5. DTM mode 3: EGR... https://www.volvoclub.org.uk/faq/Eng...agnosticCodesi