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Hesitation at lower rpms

cmsuter

cmsuter

Member
Joined
Feb 11, 2019
91 245. I'm chasing an issue. My wagon has quite a drag/hesitation until maybe 2000rpm or so (don't know because there's no tach). Seems to get a bit better after it warms up. Below is everything I have done as a possible remedy:

- Tune up (plugs which were correctly gapped, wires, cap/rotor, air filter)
- Both fuel pumps and filter
- New seals and caps on all injectors
- Replaced a couple suspicious vacuum lines
- Swapped a good MAF from another 240 that runs great
- Swapped ignition coil
- New FPR
- Retimed
- Intake hose has no holes

I checked codes and had 3-2-2 (Mass Air Flow sensor burn-off signal missing or faulty (MAF wiring fault). I cleared it and it doesn't seem to have had any effect.

I keep thinking vacuum leak but I just can't seem to find any leaks.
 
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If you have a timing light, check that the ignition is advancing when the throttle is first opened. This was traditionally called the vacuum advance. A mechanical advance would then occur at a higher rpm.
 
It does sound a lot like an intake leak. The plastic accordion tube that goes from the throttle body to the MAF often cracks from age and engine movement. Its also really easy to remove check.

To test fuel pressure you'll need to find or make an inline adaptor to T in the pressure gauge. Some of the more expensive fuel pressure test kits come with them already. The other option is swap the fuel rail to the 92+ version with the schrader valve if you have access to one.
 
Bump. Still having this issue and it seems to be getting worse. I updated the list to show everything that has been done to fix this issue.
 
What do you mean by 'retimed'? cam timing? Did you also check if the auxiliary shaft is also timed correctly? That shaft drives the dizzy so if that shaft has jumped a tooth it means the ignition will have retarded also.
 
Meaning I essentially pulled the belt and reapplied it. In case something jumped a tooth, I just reset everything.
 
Not backfire. This popping back through the intake. I have retimed the motor. I'm fairly confident its timed correctly. But if it was off, I would think the issue would be consistent. This issue is maybe 60-70% of the time
 
Have you measured valve lash? if it pops back through the intake it may mean the intake valves are adjusted too tight.(meaning they won't close perfectly)
 
I haven't measured valve lash. I can't imagine that'd be causing my hesitation issue would it?
 
Bump. Resorted to taking it to a shop who specializes in older Volvos and they also couldn't find the issue.
 
Big vac leaks affect the engine most at low RPM/highest vacuum. Does it also idle poorly when it's cold, need throttle input to keep from stalling or any of that? Can't hurt to check the coolant temperature sensor too

cmsuter said:
I have retimed the motor. I'm fairly confident its timed correctly.
Click to expand...

The timing marks on the pulleys line up with the marks on the rear timing cover or they don't. Not picking on you, rather just trying to keep it real here - the cam, int. shaft and crank pulleys are either right or wrong unless you have an adjustable pulley
 
woodenpudden said:
Big vac leaks affect the engine most at low RPM/highest vacuum. Does it also idle poorly when it's cold, need throttle input to keep from stalling or any of that? Can't hurt to check the coolant temperature sensor too



The timing marks on the pulleys line up with the marks on the rear timing cover or they don't. Not picking on you, rather just trying to keep it real here - the cam, int. shaft and crank pulleys are either right or wrong unless you have an adjustable pulley
Click to expand...

What I meant was that verifying the timing was one of the first things I did. It's pretty easy to mistakenly set one of the gears off a tooth and not realize it. When you do that, it obviously runs poorly. So what I'm saying is, I'm fairly confident that timing isn't the issue.

It has a slightly rough idle all the time. Hot or cold. It does not want to stall when idling. When it's cold, if you give it a lot of gas, sometimes it will bog and probably would stall if I kept my foot in it.
 
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