Engine surging problem
Discussion
I've just come across my 1st problem with my newly acquired 390SE.
If I drive it at a steady speed between 30 & 40 MPH in 4th the car seems to surge all the time unless I change down to 3rd. At higher speeds it's fine and it accelerates smoothly.
I have checked the timing which has been set to 4 degrees and it has a new set of Magnecor leads on it.
Thanks
If I drive it at a steady speed between 30 & 40 MPH in 4th the car seems to surge all the time unless I change down to 3rd. At higher speeds it's fine and it accelerates smoothly.
I have checked the timing which has been set to 4 degrees and it has a new set of Magnecor leads on it.
Thanks
nwarner said:
at a steady speed between 30 & 40 MPH in 4th the car seems to surge all the time
There's a tendancy to drive line shunt where the engine bangs backwards and forwards on the transmission, is this what you're experiencing? It is an inherent problem at very low rpm but can be made worse if the engine is out of tune and also if the transmission has more backlash than normal.There's another effect known as surging where the engine keeps pulling but it feels as if you are varying the throttle every few seconds although the throttle is actually constant. This can be caused by the engine running too lean, which could be cause by any of the relevant sensors being faulty.
chedder said:
Could be few things that can cause the problem, what is the idle speed on tickover?
If that is to high then that can cause some shunt at low throttle openings.
4* on the timing may not be enough, try moving it to 8* and see if that improves it.
Chedder
The Idle speed at tickover is about 700rpm so probably not that. I'll try it at 8* and see if there's a difference.If that is to high then that can cause some shunt at low throttle openings.
4* on the timing may not be enough, try moving it to 8* and see if that improves it.
Chedder
GreenV8S said:
There's a tendancy to drive line shunt where the engine bangs backwards and forwards on the transmission, is this what you're experiencing? It is an inherent problem at very low rpm but can be made worse if the engine is out of tune and also if the transmission has more backlash than normal.
There's another effect known as surging where the engine keeps pulling but it feels as if you are varying the throttle every few seconds although the throttle is actually constant. This can be caused by the engine running too lean, which could be cause by any of the relevant sensors being faulty.
It's more like the engine keeps pulling but it feels as if I'm are varying the throttle every second. It has just been MOT's and the readout for the CO2 etc. does show it to be running lean. I also noticed this morning when I started it that it wouldn't run very well untill it warmed up a bit.There's another effect known as surging where the engine keeps pulling but it feels as if you are varying the throttle every few seconds although the throttle is actually constant. This can be caused by the engine running too lean, which could be cause by any of the relevant sensors being faulty.
Thanks
You have a tuning problem, but while previous suggestions of incorrect timing are right i would see to the lean running first, otherwise you will cause pinking/overheating which is not good!
Just for reference my 89 390se runs at 12 degrees BTDC, the dyno showed no more pinking than at 8 but alot more power is produced at 12, just make sure you use good fuel!
Just for reference my 89 390se runs at 12 degrees BTDC, the dyno showed no more pinking than at 8 but alot more power is produced at 12, just make sure you use good fuel!
TVR Power will tell you to run at 12 degrees, but you will need at least 98 petrol, i either use shell v power or the 99 octane available at tesco, it depends on where i am when i need it.
My car used to run at 8 degrees, but when i altered it the power delivery below 2500rpm was shall i say different (like someone had dropped another engine in). It used to be dull and flat then when it hit 2.5K it took off like a rocket(interesting results on wet roundabouts) now it is alot smoother,more controllable and is producing alot more power and torque.
My car used to run at 8 degrees, but when i altered it the power delivery below 2500rpm was shall i say different (like someone had dropped another engine in). It used to be dull and flat then when it hit 2.5K it took off like a rocket(interesting results on wet roundabouts) now it is alot smoother,more controllable and is producing alot more power and torque.
Edited by sphs2 on Saturday 21st February 14:03
nwarner said:
If I drive it at a steady speed between 30 & 40 MPH in 4th the car seems to surge all the time unless I change down to 3rd. At higher speeds it's fine and it accelerates smoothly.
I have checked the timing which has been set to 4 degrees and it has a new set of Magnecor leads on it.
Your timing at 4 deg BTDC is fine for the lowest grade of unleaded and it will not be pinking, so no damage either by pre-ignition. If you decide to go for a higher octane fuel then perhaps another 4 degrees (total 8) might allow you to prevent pinking still. Anything more than that will be empirical, depending as it does on many factors, as discussed here:I have checked the timing which has been set to 4 degrees and it has a new set of Magnecor leads on it.
http://www.vintagemodelairplane.com/pages/Snippets...
Regarding the surging, Methinks 30 to 40 mph in 4th is too high a speed for it to be due to running near idle rpm inducing drive line shunting, but more likely to be due to a rogue air leak into the plenum chamber creating an uncontrollable weak (low energy/low torque) mixture at that particular rpm but eliminated by dropping a cog and inducing a richer input from the ECU. Air leaks are easily tested for and fixed:
http://www.vintagemodelairplane.com/pages/Rover_Te...
And the suggestion of a Throttle Pot fault is also valid but those surges tend to be very random due to the random nature of the electrical noise firing the acceleration enrichment circuits, not rythmic as you seemed to indicate, unless I read it wrong.
Either way, IF you are new to the system, a good component testing program will help you no end. If you cant find one elsewhere, there is lots of stuff accompanying the above links.
Edited by honestjohntoo on Saturday 21st February 21:41
You don't say if the engine is flapper type or hot-wire, on an 87 car it could be either.
At the back of the plenum chamber on the flapper ignition cars is an overrun valve, this opens if the plenum vacuum exceeds a set amount. The spring on these gets tired with age and generally causes idling issues where the unit opens, lets in more air and the engin surges. I suppose that this could cause problems on the road at low throttle.
Try temporarily blocking this valve off and if it cures the shunting, tighten up the adjuster on the valve. Don't overdo it because then you will get oil sucked back through the valve guides when on trailing throttle going downhill - and a very blue cloud when you next accelerate.
The other source of shunting like this (that hasn't already been suggested) is the resistor pack on the passenger side inner wing. If the car has been unused for a while and the connections corroded a bit then you could be getting problems with this breaking and re-making when the car shudders.
Russ
At the back of the plenum chamber on the flapper ignition cars is an overrun valve, this opens if the plenum vacuum exceeds a set amount. The spring on these gets tired with age and generally causes idling issues where the unit opens, lets in more air and the engin surges. I suppose that this could cause problems on the road at low throttle.
Try temporarily blocking this valve off and if it cures the shunting, tighten up the adjuster on the valve. Don't overdo it because then you will get oil sucked back through the valve guides when on trailing throttle going downhill - and a very blue cloud when you next accelerate.
The other source of shunting like this (that hasn't already been suggested) is the resistor pack on the passenger side inner wing. If the car has been unused for a while and the connections corroded a bit then you could be getting problems with this breaking and re-making when the car shudders.
Russ
I didn't get a chance to look at the problem until last week and by then it had got a lot worse. It had started surging most of the time, pinking under load and during acceleration and misfiring occasionally.
I first of all changed the timing from 4 degrees to 8 degrees and got the CO2 adjusted from 1 to 1.5. All that did was make the pinking even worse.
I changed the timing to 0 degrees and surging got worse and pinking stayed the same so changed it back to 4.
I then checked all the air hoses for splits etc. on the plenum and fitted some jubilee clips to hoses without. No change.
I replaced the AFM with another known to be good. No change.
I replaced the extra air valve with another known to be good. No change.
I checked the throttle pot. and that was OK with smooth readings.
I checked the overrun valve and that seemed a bit loose but when I tried the adjuster I found that it was very loose to turn and doesn't tighten. I blocked it off but still no difference.
The fuel pressure regulator looks very new so I haven't done anything with this.
I have disconnected the vacuum advance on the distributor but that made no difference.
The car is fitted with a new looking Mallory distributor, coil and Hyfire 6A ignition system.
Apart from taking the plenum off, cleaning and resealing it I've run out of ideas. Has any one else got any ?
I first of all changed the timing from 4 degrees to 8 degrees and got the CO2 adjusted from 1 to 1.5. All that did was make the pinking even worse.
I changed the timing to 0 degrees and surging got worse and pinking stayed the same so changed it back to 4.
I then checked all the air hoses for splits etc. on the plenum and fitted some jubilee clips to hoses without. No change.
I replaced the AFM with another known to be good. No change.
I replaced the extra air valve with another known to be good. No change.
I checked the throttle pot. and that was OK with smooth readings.
I checked the overrun valve and that seemed a bit loose but when I tried the adjuster I found that it was very loose to turn and doesn't tighten. I blocked it off but still no difference.
The fuel pressure regulator looks very new so I haven't done anything with this.
I have disconnected the vacuum advance on the distributor but that made no difference.
The car is fitted with a new looking Mallory distributor, coil and Hyfire 6A ignition system.
Apart from taking the plenum off, cleaning and resealing it I've run out of ideas. Has any one else got any ?
Sounds like you have done quite a few of the obvious checks but as the car is a relative unknown to you .. I would check a few of the basics first.
1. Check spark at plugs is good.. do this in a dark garage gives the best result and you can just put an old set of plugs on the leads to save removing the plugs. I presume you have checked the plugs are OK and reasonable gapped (31 thou inch).
2. Check TDC is correct and also mark 8 degrees and 28 degrees on the crank. When you have marked the crank correctly - with a timing light - set timing at 8 degrees with the vacuum pipe disconnected .. and when you rev the engine - you should see the timing move towards the 28 degree marker at 4000 revs and no further.
One of the issues with a non standard dizzy - such as the Mallory is that it does not have the same advance weights as standard and at the very least you need to check these start and max values.
3. Get the base fuel pressure checked - I think it's 36 PSI at idea with the small vacuum hose blocked and the EFI setting rely on this setting being correct.
4. Worth aiming a lazer temperature guage at the headers - to see if there are any big variations - this could indicate a misfire or even a worn camshaft on particular lobes not letting misture in / out.
Good luck.
1. Check spark at plugs is good.. do this in a dark garage gives the best result and you can just put an old set of plugs on the leads to save removing the plugs. I presume you have checked the plugs are OK and reasonable gapped (31 thou inch).
2. Check TDC is correct and also mark 8 degrees and 28 degrees on the crank. When you have marked the crank correctly - with a timing light - set timing at 8 degrees with the vacuum pipe disconnected .. and when you rev the engine - you should see the timing move towards the 28 degree marker at 4000 revs and no further.
One of the issues with a non standard dizzy - such as the Mallory is that it does not have the same advance weights as standard and at the very least you need to check these start and max values.
3. Get the base fuel pressure checked - I think it's 36 PSI at idea with the small vacuum hose blocked and the EFI setting rely on this setting being correct.
4. Worth aiming a lazer temperature guage at the headers - to see if there are any big variations - this could indicate a misfire or even a worn camshaft on particular lobes not letting misture in / out.
Good luck.
nwarner said:
I first of all changed the timing from 4 degrees to 8 degrees and got the CO2 adjusted from 1 to 1.5. All that did was make the pinking even worse.
I changed the timing to 0 degrees and surging got worse and pinking stayed the same so changed it back to 4.
I then checked all the air hoses for splits etc. on the plenum and fitted some jubilee clips to hoses without. No change.
I checked the overrun valve and that seemed a bit loose but when I tried the adjuster I found that it was very loose to turn and doesn't tighten. I blocked it off but still no difference.
The fuel pressure regulator looks very new so I haven't done anything with this.
I have disconnected the vacuum advance on the distributor but that made no difference.
The car is fitted with a new looking Mallory distributor, coil and Hyfire 6A ignition system.
Apart from taking the plenum off, cleaning and resealing it I've run out of ideas. Has any one else got any ?
You checked visually and manually for air leaks but its not clear if you did the tests dynamically as recommended in the "Plenum" essay. Some components have internal airways that you cant see and some have remote functions, the essay explains.I changed the timing to 0 degrees and surging got worse and pinking stayed the same so changed it back to 4.
I then checked all the air hoses for splits etc. on the plenum and fitted some jubilee clips to hoses without. No change.
I checked the overrun valve and that seemed a bit loose but when I tried the adjuster I found that it was very loose to turn and doesn't tighten. I blocked it off but still no difference.
The fuel pressure regulator looks very new so I haven't done anything with this.
I have disconnected the vacuum advance on the distributor but that made no difference.
The car is fitted with a new looking Mallory distributor, coil and Hyfire 6A ignition system.
Apart from taking the plenum off, cleaning and resealing it I've run out of ideas. Has any one else got any ?
Dont overlook the integrity of the air intake hose and its jubilee clip connections to Tunnel and AFM.
You have also this far, missed one of the key jobs, the plenum cleaning task including its breather and idle galleries.
Given the importance stressed in the mentioned essay, its not appropriate to move on to other possibilities before the basics have been addressed.
I'm not sure if its been mentioned before but do check the integrity of the fuel supply system looking for blocked filters, crud in the tank, fuel pump and fuel lines.
Advancing the timing will create more pinking, by the way, but so it should lessen by retarding it, but apparantly it does not?
What is not clear is that pinking would only normally occur under heavy engine load (ie uphill/high gear) if you've got pinking all the while that suggests a timing issue with your aftermarket ignition system about which I am not familiar - seek an expert view on how it is supposed to behave and be set-up.
There is a remote possibility that your timing marks do not coincide with TDC of the piston due to
- pointer has been bent/moved
- Damper pulley innards damaged giving false timing reading.
You still have to verify that the fuel pressure operates in the range 26-36 psi, no lower, no higher, unless the FPR is a rising rate unit in which case you have to expect higher fuel pressure when engine speed/load demands more fuel.
Try not to run with the overrun valve blocked off, as mentioned by Russ, but you are describing a faulty valve if it will not adjust, so look into the reason why it wont adjust. Its simplicity is based on a single spring and an adjustement nut, so I cant visualise the fault you describe unless the thread is stripped.
You can run with the vaccy advance disconnected but expect to lose some sparkle when accelerating from a standstill if not functioning.
Finally I just learned a theoretical new trick to check if the throttle pot is malfunctioning. Disconnect the pot from its connector and the car should run normally EXCEPT you get no acceleration or full load enrichment. However if the pot was faulty causing random running problems then when disconnected those random problems should disapper - Or at least so the theory goes.
If it's pinking under full load either the engine has too much compression, or the fuel octane is too low, or it's too lean, or has too much ignition advance, or the cylinder is coked up causing hot spots. It could easily be a combination of these factors.
From the symptoms of surging I would think it's almost certainly running too lean as a starting point. Since you have a non-standard dizzy I would suggest you also confirm the position of TDC mechanically (easily done with a dead stop) and then find out how much mechanical advance the dizzy has and how soon it comes in (easily done with a timing light with the vacuum advance disconnected).
From the symptoms of surging I would think it's almost certainly running too lean as a starting point. Since you have a non-standard dizzy I would suggest you also confirm the position of TDC mechanically (easily done with a dead stop) and then find out how much mechanical advance the dizzy has and how soon it comes in (easily done with a timing light with the vacuum advance disconnected).
Thanks for the suggestions. I will do the tests as recommended in the "Plenum" essay at the weekend. I will also try and check the fuel pressure but hopefully it should be OK as the regulator looks very new. I'll also check the timing marks are correct and the other suggestions.
I took the plenum off last night. It was certainly stuck on well with loads of silicon sealant, especially onthe inside. The breather and idle galleries seem to be clear but I will give it a good clean before I refit it.
The overrun valve looks a bit suspect. Any idea where I might get a replacement? I tried Rimmer Brothers but they told me they are NLA.
I looked through the paperwork I got with the car and the Mallory Distributor fitted has 24 degrees advance.
I took the plenum off last night. It was certainly stuck on well with loads of silicon sealant, especially onthe inside. The breather and idle galleries seem to be clear but I will give it a good clean before I refit it.
The overrun valve looks a bit suspect. Any idea where I might get a replacement? I tried Rimmer Brothers but they told me they are NLA.
I looked through the paperwork I got with the car and the Mallory Distributor fitted has 24 degrees advance.
Edited by nwarner on Thursday 23 April 10:37
That 24 degrees will be the centrifugal advance only, non?
Regarding the fuel pressure i would be a little wary of setting it to 36psi and thinking it will be fine, my car runs extremely lean at that setting (granted it does have an as of yet unresolved issue) i would be inclined to get the fuelling checked on a dyno to make sure you're not doing damage.
Regarding the fuel pressure i would be a little wary of setting it to 36psi and thinking it will be fine, my car runs extremely lean at that setting (granted it does have an as of yet unresolved issue) i would be inclined to get the fuelling checked on a dyno to make sure you're not doing damage.
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