Sudden Engine Knock When Engaging And Disengaging Ac While Driving In Slow Speeds (10-30Kmh)

[PerfMad]

Hi Heaps

I bought a Honda City 2001 model manual car few months ago.. And recently did few repairs related to oil leaks, and one engine mount was re-bushed since it was weak and also a tune-up. However, I's experiencing a knock whenever i run slowly. Knock is coming only when the AC kicks in and kicks out. Is this normal or should I be worried?

Note : After warm up car idles in around 700-800 (not more than 800)

Edited June 21, 2016 by PerfMad

[Dushyantha]

The Ac clutch usualy makes a small knocking sound when it engages and disengages . Which is normal . and sometimes when engine mounts are rebushed without replacing them with genuine parts they end up to be a bit harder than the original . hence u might experience a small difference in feeling the engine vibrations . i once had a similar knocking sound come when accelerating or decelerating in gear after replacing an engine mount . turns out i forgot to tighten the engine mount properly . . hope its not something like that

normal engine rpm in most cars is somewhere around 750rpm . so its totally fine.

[PerfMad]

The Ac clutch usualy makes a small knocking sound when it engages and disengages . Which is normal . and sometimes when engine mounts are rebushed without replacing them with genuine parts they end up to be a bit harder than the original . hence u might experience a small difference in feeling the engine vibrations . i once had a similar knocking sound come when accelerating or decelerating in gear after replacing an engine mount . turns out i forgot to tighten the engine mount properly . . hope its not something like that

normal engine rpm in most cars is somewhere around 750rpm . so its totally fine.

Thanks for the headsup machan.. Im more worried about the knock/vibration i get.. not the sound.. The thing is when i bought the car i cant remember having this sort of knock(not 100% sure, but can't recall it).. I even hardly realized, that Ac is on/off..

But since I had many oil leaks, my garage advised to remove the whole engine from the car and replace all the seals (since oil was leaking from almost all the seals, so i wanted to replace all seals related to engine)

Im just worried could this be due to that?? I mean after fixing something went wrong ?

[LancerL]

How do you feel when the car is not running and on idle.

[Dushyantha]

Try to hold the engine from some sturdy part and rock it back and fort and see if the sound comes . If its some kind of vibration knock . then it possible that a mount or some engine mount bracket has not been fixed properly . the AC clutch engaging or disengaging only makes a small sound and doesnt make a vibration type of knok . so better get it checked

[PerfMad]

On 6/21/2016 at 8:39 PM, LancerL said:

How do you feel when the car is not running and on idle.

in idle it works smoothly .. i can hardly feel AC is engaging and disengaging..

However my car is a manual, so when i speed within 20-40kmh range and lets say i shifted from 1st to second gear when speed is 20kmh and if suddenly AC kicks in during that time, i feel it bit hard, with a sudden vibration.. other than that it not noticeable 

[Rumesh88]

Does car rev up to around 2000rpm and come down smoothly to 800 range on a cold start with AC off after a couple of minutes (may take longer due to low temperature even in Colombo these days)? Then  with the car fully warmed up and AC switched off, very slowly rev up to 1500 rpm range and observe for any irregularity in RPM (or a engine vibration, a miss in the beat) at any point within the RPM range 800 to 1500. These two observations can be done just to see if the IACV and TPS working as expected.

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Edited November 18, 2016 by Rumesh88

[PerfMad]

1 hour ago, Rumesh88 said:

Does car rev up to around 2000rpm and come down smoothly to 800 range on a cold start with AC off after a couple of minutes (may take longer due to low temperature even in Colombo these days)? Then  with the car fully warmed up and AC switched off, very slowly rev up to 1500 rpm range and observe for any irregularity in RPM (or a engine vibration, a miss in the beat) at any point within the RPM range 800 to 1500. These two observations can be done just to see if the IACV and TPS working as expected.

 

Hi Rumesh88 - When engine is cold RPM sits at 1500 and then slowly cm down to 800, I never felt any miss though.. i feel it specially lets say i go in the 2nd gear and speed is around 20-30 and if i take the leg off from the padel, then also i get a sort of a jerk.. is that normal...?  Same sort of jerk comes when AC engages and kick off during above mentioned speed limit specially..

However i can check what u told, and give my feedback today..

[Rumesh88]

1 hour ago, PerfMad said:

Hi Rumesh88 - When engine is cold RPM sits at 1500 and then slowly cm down to 800, I never felt any miss though.. i feel it specially lets say i go in the 2nd gear and speed is around 20-30 and if i take the leg off from the padel, then also i get a sort of a jerk.. is that normal...?  Same sort of jerk comes when AC engages and kick off during above mentioned speed limit specially..

However i can check what u told, and give my feedback today..

No you should not get a jerk even if you suddenly take the foot off. The ECU reacts to the sudden closure of the throttle to avoid stalling unless of course for some reason the engine is operating at a lower power point than what it is designed for. Could you get your plug wires checked for continuity (ie if they are something like between 3k ohms to 20k ohms ) before going into other things?

[PerfMad]

1 minute ago, Rumesh88 said:

No you should not get a jerk even if you suddenly take the foot off. The ECU reacts to the sudden closure of the throttle to avoid stalling unless of course for some reason the engine is operating at a lower power point than what it is designed for. Could you get your plug wires checked for continuity (ie if they are something like between 3k ohms to 20k ohms ) before going into other things?

Ok I will get it checked tomorrow and update you on that.. is there anything else that needs to be checked after that? if everything is fine..

P.S. There were two instances where when i start the car initially i felt sort of a miss, but it was there for like 10-20 secs and just vanished and never came back again... 

[Rumesh88]

Being a marginal issue, it can be almost anything to do with the engine but usually the issue will not show up in a scan. So what you should do is to eliminate all the possibilities that you can check and rectify externally without first going into internals of the engine. If the plug wires are ok, then check your plugs - one or more could have a weak spark hence more deposits on it, PCV,  look for possible vacuum leaks in the inlet manifold area, TPS for dead spots, injectors for uniform fuel delivery, cylinder compression, and even a second look at IACV although it seems to work it may still have a sluggish response to a sudden change in the air flow. Although we tend to assume that IACV is active only when it is idling it is not really the case. As the throttle is opened, IACV also follow the pattern and retract itself to keep the idle air path open so that in the event of a sudden throttle closure IACV can bring the RPM slowly down to prevent engine from stalling. This is analogues to dash pots at the throttle mechanism in carb engines.

[PerfMad]

36 minutes ago, Rumesh88 said:

Being a marginal issue, it can be almost anything to do with the engine but usually the issue will not show up in a scan. So what you should do is to eliminate all the possibilities that you can check and rectify externally without first going into internals of the engine. If the plug wires are ok, then check your plugs - one or more could have a weak spark hence more deposits on it, PCV,  look for possible vacuum leaks in the inlet manifold area, TPS for dead spots, injectors for uniform fuel delivery, cylinder compression, and even a second look at IACV although it seems to work it may still have a sluggish response to a sudden change in the air flow. Although we tend to assume that IACV is active only when it is idling it is not really the case. As the throttle is opened, IACV also follow the pattern and retract itself to keep the idle air path open so that in the event of a sudden throttle closure IACV can bring the RPM slowly down to prevent engine from stalling. This is analogues to dash pots at the throttle mechanism in carb engines.

OK machan.. thanks for the headsup.. I will get each of these tested one by one, if the spark plugs and wires are in good shape.. 

[PerfMad]

Hi Rumesh88

I just showed mine to my mechanic (mech ge golaya tamai baluwe), he went with me for a ride and i showed him the exact issue, he said it can be overcome by advancing the ignition (by rotating the distributor position), by doing so Rev increased upto 1000 from 850... Then I told him it got increased and he reduced it, didnt see how it was reduced.. however after adjusting the distributor position, he said now this should be good and go for a ride and see.. but i felt the same feeling. So i took the car because i was in a hurry to to go somewhr else and i told him i will put the car again on friday to get it checked..

My question is,

What he did was correct? (adjusting the distributor position) ??
What are the pros and cons in doing so?

 

Im gonna ask him to start testing from spark plugs and plug wires on friday, cz this knock is really annoying when driving in low gears specially...

[Rumesh88]

2 hours ago, PerfMad said:

Hi Rumesh88

I just showed mine to my mechanic (mech ge golaya tamai baluwe), he went with me for a ride and i showed him the exact issue, he said it can be overcome by advancing the ignition (by rotating the distributor position), by doing so Rev increased upto 1000 from 850... Then I told him it got increased and he reduced it, didnt see how it was reduced.. however after adjusting the distributor position, he said now this should be good and go for a ride and see.. but i felt the same feeling. So i took the car because i was in a hurry to to go somewhr else and i told him i will put the car again on friday to get it checked..

My question is,

What he did was correct? (adjusting the distributor position) ??
What are the pros and cons in doing so?

 

Im gonna ask him to start testing from spark plugs and plug wires on friday, cz this knock is really annoying when driving in low gears specially...

That a perfect makabaas way to do it - ie to assume a fault and adjust ignition timing to overcome an issue. Did he use a timing torch (strobe light) to adjust the timing?. If he does not have the tool he cannot do a proper job in this car. Change your mechanic and get the timing adjustment properly re-done.

[PerfMad]

1 hour ago, Rumesh88 said:

That a perfect makabaas way to do it - ie to assume a fault and adjust ignition timing to overcome an issue. Did he use a timing torch (strobe light) to adjust the timing?. If he does not have the tool he cannot do a proper job in this car. Change your mechanic and get the timing adjustment properly re-done.

Nope, actually it wasnt the mech, mech's golaya only did it..he didnt use anything, he just used moved it abit based on the sound it revs i guess.. but since the idle was bit higher i think he kept it the same location (not quite sure though).. I really need to get this sorted. all this time i thought this may b due to manual, didnt no it was an issue, until you explained it..

 

Is there any good place that you can recommend ? How much will it cause just to get this timing re-done the way you mentioned ?

Edited November 21, 2016 by PerfMad

[Rumesh88]

On 11/21/2016 at 2:48 PM, PerfMad said:

Nope, actually it wasnt the mech, mech's golaya only did it..he didnt use anything, he just used moved it abit based on the sound it revs i guess.. but since the idle was bit higher i think he kept it the same location (not quite sure though).. I really need to get this sorted. all this time i thought this may b due to manual, didnt no it was an issue, until you explained it..

 

Is there any good place that you can recommend ? How much will it cause just to get this timing re-done the way you mentioned ?

I cannot recommend a mechanic for Hondas other than the agent I'm afraid. I leave it for other Honda enthusiasts in the forum to comment on. If the issue was due to timing then either it should have become better or worse by now.  You can get it checked and readjusted if necessary when you do a tune up again. BTW does it always happen in second gear but not in others?

[PerfMad]

2 hours ago, Rumesh88 said:

I cannot recommend a mechanic for Hondas other than the agent I'm afraid. I leave it for other Honda enthusiasts in the forum to comment on. If the issue was due to timing then either it should have become better or worse by now.  You can get it checked and readjusted if necessary when you do a tune up again. BTW does it always happen in second gear but not in others?

even after the adjustment, i dont feel any difference in timing though ( i think he just set it back to usual state, since i complained rev have increased ).. however, if i release the gas padel suddenly, then i will get the knock in 1st and 2nd gears specially. But if i release it slowly then it will reduce smoothly without a knock..

 

Could this be due to petrol starvation ? I dont think mine have replaced the fuel filter nor fuel pump and currently ODO meter reading is close to 190K.. Do you think its better to do a tuneup again? I did one like 6 months ago, due to lack of pulling power.. after the tuneup it was resolved, and still it has good pulling power..

But i dont think they checked the fuel pump pressure..

[Rumesh88]

Better if you can get fuel pressure checked because it can be due to fuel starvation. Also you need to ensure if your IACV is working properly (ie it moves through its full range of motion). Did they remove and clean the IACV last time at the tune up? See if the knock occurs when you are in 1st or 2nd gear and suddenly take the foot off when the RPM is at or below 1500.

[PerfMad]

11 minutes ago, Rumesh88 said:

Better if you can get fuel pressure checked because it can be due to fuel starvation. Also you need to ensure if your IACV is working properly (ie it moves through its full range of motion). Did they remove and clean the IACV last time at the tune up? See if the knock occurs when you are in 1st or 2nd gear and suddenly take the foot off when the RPM is at or below 1500.

I wasn't there when they did the tuneup (since it was done on a weekday).. they said they cleaned all the sensors and plugs and wires were in good shape so no need to replace as well.

I will start with the fuel pressure then.. Just curious what should be the standard value (as in for an example if the value is less than X, then its preferred to change the pump) ?

And i'll check whether it will make the knock is below 1500.. However just curious, either way (even if its below or above 1500) it shouldn't make a knock right? 

[Rumesh88]

If it does not occur below 1500 RPM chances are that your IACV is not moving as it should be. It shouldn't make a knock at any stage.  As for fuel pressure I don't have the exact figure for the model but from the top of my head the pressure with engine stopped should be 50 psi and with the engine on idle it should be around 40 to 45 psi.

[PerfMad]

4 minutes ago, Rumesh88 said:

If it does not occur below 1500 RPM chances are that your IACV is not moving as it should be. It shouldn't make a knock at any stage.  As for fuel pressure I don't have the exact figure for the model but from the top of my head the pressure with engine stopped should be 50 psi and with the engine on idle it should be around 40 to 45 psi.

Ok machan, i will check this today evening and update you on my findings.. Im planning to put the car to garage again to resolve this and one of my rear suspension sound .

So i wanted to filter out to least possible issues, that could lead to this prob, rather than replacing or doing any unwanted things blindly..

[PerfMad]

@Rumesh88 i checked it today, and there were instances where i didnt get the knock when the engine was bit cold, but once its in working temp. i felt the knock even within 1500 rpm range most of the time..

So as for ur tips, i should start with IACV sensor and then fuel pressure, spark plugs and wires? I personally dont think doing a engine tuneup will be better, i rather check for specifics like above, isnt it?

 

just curious could this be due to a vacuum leak or something as well? do you think i may need to replace this unit? if so any idea how much will it cost?

Edited November 23, 2016 by PerfMad

[Rumesh88]

As I said before issue being a marginal one it is difficult to home in on a particular area and it can be due to one or more of many possibilities. Hence what to do first is a matter of luck. But it in only logical to begin with least difficult inspections (like plugs, wires, throttle adjustment, fuel pressure, IACV, possible vacuum leaks). Do not come to the conclusion that you would have to replace IACV for now. In fact if properly done one should be able to identify and rectify the issue in a tune up which again consists of all the things mentioned above and a few more done in one go.

[PerfMad]

13 hours ago, Rumesh88 said:

As I said before issue being a marginal one it is difficult to home in on a particular area and it can be due to one or more of many possibilities. Hence what to do first is a matter of luck. But it in only logical to begin with least difficult inspections (like plugs, wires, throttle adjustment, fuel pressure, IACV, possible vacuum leaks). Do not come to the conclusion that you would have to replace IACV for now. In fact if properly done one should be able to identify and rectify the issue in a tune up which again consists of all the things mentioned above and a few more done in one go.

Thanks @Rumesh88 i will update you on the findings .. thanks for the headsup

[PerfMad]

Hi @Rumesh88

Today i checked below areas:

- Spark plugs (in good condition- including the gap) [Checked with some used iridium plugs as well]

- Spark wires (seems good as well)

- Cleaned distributor cap and contacts

- Cleaned throttle body and checked the adjustment

- Cleaned IACV

- Checked fuel pressure and it was having 60PSI

- Checked and replaced fuel filter as it was bit clogged

- Finally did timing adjustment again and revert it to original state as well

But still the knock is there... Mechanic told, that he needs to take the cover off and check the timing (i'm not quite sure whether they removed the timing belt during my oil seals replacement which was done 5months ago[i had lot of oil leaks therefore i asked them to replace all oil seals in engine bay]), but i cant remember whether i had this knock before

I'm clueless, can you please shed some light ? I would highly appreciate ur inputs on this..

Edited November 29, 2016 by PerfMad