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Old 08-19-2009, 08:16 PM   #1
BruceAlmighty
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Default weird hesitation under load

hi everyone and thanks for checking out my thread. im actually not new to the site, as i was a member a few years ago, and owned several Volvo's myself. however, ive forgotten my screen name and password, so this one will have to do. lol

anyways, im a mechanic by trade. maybe not the best there is, but i can fix most problems. my parents have three Volvo's, one of which is a 92 240. they purchased this car about a year ago and is wasnt running right, so they asked me to take a look at it. i noticed that the timing was off and the belt looked rough. i made some recommendations to them and i got to work. after all was said and done, i had replaced the timing belt, plugs, wires, cap, rotor, thermostat, water pump, fuel filter, and air filter(if it seems like im rambling, im not. theres a reason im stating all of this).

after doing the work, the car has an incredibly weird hesitation. at idle, the car runs great, but under load, it acts as if its running out of fuel. it only does this to a certain rpm (my guess is about 2500), then the car regains full power and runs great. it will start running like crap again once the rpms get below the point stated above. the timing is spot on, compression is 190psi across the board, both fuel pumps are functioning, the ignition coil is working correctly, no blown fuses, the cat isnt stopped up, no fuel leaks, nothing.

i have checked all of the basics and everything has come back fine. my parents were getting a little impatient with me, and rightfully so, so they took it to what was supposed to be a reputable Volvo shop close by. after $900 and having a new, MAF, TPS, and crank sensor installed, the car still runs the same. the shop said that it had two bad valves, but i know that if it did, one of the cylinders would have low/no compression and would run like crap constantly.

i think ive covered everything i can think of and i apologize for the extremely long post. just wanted to give the full scenario so that you would know what im dealing with. this car has me stumped guys. any and all help or suggestions would be greatly appreciated.

thanks

-Bruce-
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Old 08-19-2009, 08:21 PM   #2
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Does the engine temperature affect this at all? Could the tone ring on the flywheel be damaged, creating a bad RPM signal?
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Old 08-19-2009, 08:51 PM   #3
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engine temperature does not affect anything. whether its ice cold, or scorching hot it still runs like this. its possible that the ring could be damaged, as i didnt check that out. however, i would assume that if it was damaged, it would run rough through the entire rpm range, but i could be wrong.
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Old 08-19-2009, 09:01 PM   #4
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you said your pumps are working, but have you checked fuel pressure? any chance the fuel filter is in backwards?
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Old 08-19-2009, 09:09 PM   #5
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Cam timing off.
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Old 08-19-2009, 09:47 PM   #6
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Or intermediate shaft? Have you re-set base timing on the belt?
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Old 08-19-2009, 11:51 PM   #7
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I agree w the cam timing, if you are checking timing w a timing light ignition timing (and therefor intermediate shaft) can be bang on but you will never see cam timing being off by a tooth.
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Old 08-20-2009, 09:17 AM   #8
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Sounds like you have the classic symptoms of a clogged converter. Pull it off and take it for a spin around the block. Let us know what this test yields!
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Old 08-20-2009, 01:50 PM   #9
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the fuel filter is in the right way and the fuel pressure is good. ive re-checked all the timing marks three times and also had a few mechanic friends check it as well. they are all spot-on.

i was wondering about the cat, but it seems to run too well once it regains power to be a stopped up cat. if i put the car in 2nd gear and get it above 2500rpms or so, the car runs great the entire time. its only once the car shifts and rpms drop that it falls on its face again.

thank you guys for all your input so far.
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Old 08-20-2009, 02:14 PM   #10
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Manual or automatic?
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Old 08-22-2009, 12:50 PM   #11
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its an 89 automatic. the cat is flowing just fine and functioning the way it should be. i checked the other day for flow and temperature.

this issue has me so boggled. my co-workers have no input either. in all my years of working on cars, ive never encountered a car i couldnt fix. :(
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Old 08-22-2009, 01:03 PM   #12
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You need to recheck that timing belt alignment.
Advanced cam timing will cause poor low rpm acceleration.
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Old 08-22-2009, 01:15 PM   #13
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Did it have this hesitation before the work? Maybe the cam has been changed, and needs to be retarded. Have you checked valve clearance?
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Old 08-24-2009, 08:36 PM   #14
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it had a hesitation, but just a slight stutter. nothing like what im experiencing now. the cam is still the same, so thats been ruled out. have now checked valve clearances yet, but i know they need to be adjusted. ive just been trying to get rid of this hesitation before i go any further.

i guess im going to tear the timing belt back down again and re-time there. ive run out of all other possibilities at this point.
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Old 08-27-2009, 06:33 PM   #15
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How does it act at WOT out of gear? I have a 90 740 Gl that seems like it is doing the same thing.
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Old 06-02-2021, 06:07 PM   #16
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Default Bump on old thread, weird hesitation under load

Bumping this thread hoping there was a solution?

Similar problem in my 92 240, started after a timing belt change... Timing seems to be all correct, all the gears are lined up but still misfiring in middle rpm range, runs fine once it gets up to speed.
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Old 06-03-2021, 07:33 AM   #17
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Although the old thread had several suggestions to re-examine the tbelt alignment, I didn't see any specific attention to the I-shaft or distributor. The OP's clue that the timing was off is vague, but I've seen where experienced mechanics immediately want to turn the dizzy to fix ignition timing that is referenced from the crank.

This dizzy is supposed to be locked in place rotation-wise by a plastic insert, so the insert is tossed or the dizzy is pulled and re-inserted a cog off. If the distributor timing is indeed unmolested, a parallax error setting the I-shaft timing mark can put the distributor rotor physically out of reach of the spark only at greater advance settings depending on which way it is off despite the wide contact design in the rotor.

Bottom line is the car is broken by the attempt to fix it. Problem is, the I-shaft error could have been intentional at the last tbelt change to compensate for messing with the dizzy, and now you've put it back where it belongs. Check it carefully with good light and a mirror, or try this shortcut:

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Old 06-03-2021, 09:19 AM   #18
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Picture of disti alignment at TDC (it's off a tad - the hold-down bolt hole isn't quite centered in the picture). Notice the scribe mark in the edge of the disti housing versus the tip of the rotor:
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Old 06-04-2021, 08:25 PM   #19
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Thank you for the pointers! I took the whole darn thing apart today and re-timed it. All of the marks are aligned, even after a couple rotations. 44 teeth between the cam and the I-pulley, and the dizzy is spot on to that mark. And it is still misfiring when I wind it up.
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Old 06-07-2021, 11:26 AM   #20
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Bad plugs and wires?
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Old 06-07-2021, 12:28 PM   #21
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I don't have a good test for this except watching the spark timing advance while opening the throttle. If the spark is advancing too far or too fast right off of idle, this would cause the engine to stumble especially under load. At higher rpm the engine would be more tolerant of the advance. You might try retarding the timing just to see if it makes a difference in the problem.

A weak spark might also cause the problem. You might try pulling the coil wire. Put a screw in the coil socket and hold the coil wire so you can see the arc. Then gently rev the engine too see if the spark intensity remains strong.

Last edited by johfraser; 06-07-2021 at 12:33 PM..
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Old 06-10-2021, 02:16 PM   #22
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Brand new plugs and wires, rotor and cap have maybe 6 months on them and they look clean. I checked the spark timing and it looks to be right, I'll do a little more investigation as to whether it's advancing too fast. Before I had made sure there were 44 teeth between the camshaft mark and I-pulley, I had timed it to the marks and then retarded the cam sprocket 1, 2, and 3 teeth, just to see if that was my issue. Car ran more or less the same with the 1 and 2 tooth retard, 3rd tooth brought on a lope at idle, wasn't running that great otherwise hahah. I swapped the coil with a known good coil and the same issue manifested. Brand new gas pumps and filters, since that was thought to be the original issue. I appreciate all the input! My next steps are the FPR and checking the injectors. Let me know any other ideas!!
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Old 06-11-2021, 04:51 PM   #23
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I'm not clear if we're dealing with a misfire or hesitation.

Hesitation is a temporary event that happens in response to say a throttle opening. If the throttle is opened some amount and then held steady, the engine fails to respond immediately but does eventually without any other change.

In contrast, a misfire would continue indefinitely if everything else is held constant.

Small changes in cam timing should only change the power curve but the engine should still operate smoothly. Its possible that the problem is not related to the timing belt change but just started happening at the same time by chance.

I still favor a spark advance issue but maybe an air flow sensor problem or injector signal. Maybe even a bad electrical connection that resonates with certain engine speed.
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Old 06-12-2021, 12:38 AM   #24
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So I put the timing light on it today to take a second look at the timing, and found out that what's happening is an intermittent spark on cylinders 1 and 4. I checked the coil wire and the issue is present coming from the coil. So not a distributor problem.

I don't have a tach handy at the moment, but my best guess is that this is manifesting around 2000 rpm and then disappears again around 2500 or 3000. This guess is based on that it starts misfiring just before it shifts from first to second, unless i am really creeping, and stops misfiring around 65 in overdrive, if that tracks. Unlike the OP, this happens under load or not. So, I suppose I could start a new thread (and probably will after this post), but I figured since you guys were here... Lmk, any questions or ideas?
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Old 06-12-2021, 10:28 PM   #25
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So, you have a clamp-on style timing light? You clamp it on each plug wire and #1 and #4 yield an intermittent flashing and #2 and #3 yield a steady flashing?

You also clamp the timing light onto the coil wire and see an intermittent flashing?

I would put a 12V test lamp on the low side coil terminal and ground. The ignition module is basically just a switch to ground so you will see 12V pulses there. If that shows an intermittent flashing I would check all the connections to the module. There is also a flywheel sensor on the back end of the head. Check its connections at each end too.
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