flat spot at 3000 rpm ?
Discussion
Hi
i have recently fitted a gas flowed inlet manifold to the 400se. Whilst it was off the road, (one thing led to another!) and i ended up fitting, new dist. cap, rotor arm, magnecor leads, Bosch coil, silicon inlet hose between plenum and afm, removed the hot spot beneath the plenum etc.
The car now starts, ticks over and generally drives ok, however it just doesn't seem that lively and there does appear to be a flat spot around the 3000rpm ?
Before i start swapping things back, any likely suspects or might it need re setting up (mixture etc)?
i have recently fitted a gas flowed inlet manifold to the 400se. Whilst it was off the road, (one thing led to another!) and i ended up fitting, new dist. cap, rotor arm, magnecor leads, Bosch coil, silicon inlet hose between plenum and afm, removed the hot spot beneath the plenum etc.
The car now starts, ticks over and generally drives ok, however it just doesn't seem that lively and there does appear to be a flat spot around the 3000rpm ?
Before i start swapping things back, any likely suspects or might it need re setting up (mixture etc)?
Hi
i have removed and refitted the trumpet base/plenum with some paste to make sure the seal between them is air tight. I also had a replacement throttle pot and a set of plugs so they've been fitted, unfortunatley i haven't had time to test dive yet.
When fitting the plugs, I noticed that all the old plugs were sooty/black, am i rght in thinking this inplies the engine is running rich? if so how do i sort this and how would running rich effect driving?
i have removed and refitted the trumpet base/plenum with some paste to make sure the seal between them is air tight. I also had a replacement throttle pot and a set of plugs so they've been fitted, unfortunatley i haven't had time to test dive yet.
When fitting the plugs, I noticed that all the old plugs were sooty/black, am i rght in thinking this inplies the engine is running rich? if so how do i sort this and how would running rich effect driving?
Edited by johntom on Sunday 18th April 22:36
IF - The orig throt pot was faulty causing spurious acceleration enrichment signals, then that would also show up as sooty spark plugs but you do not report the typical bunny-hopping that usually accompanies that fault.
BUT, your flat spot may also have been caused by a faulty throt pot NOT sending ANY acceleration enrichment signals to the ECU because it was not connected properly or the wiper/carbon track were FUBAR.
So - on the horns of a dilemma you gorra try out the new throt pot before moving on.
However, from described symptoms and reported changes you deffo have a lot of work to do, some as as already pointed out. Recap -
o Check ign timing.
o Check vacuum advance by sucking on the vac pipe and listen/watch for the dissy advance function.
o Check dissy mechanical advance - crudely - by visual inspection and turning the rotor arm against the advance springs, ensuring it has resistance and springs back OK.
o Check for disturbed connections.
In Addition
o Did you seal the hotspot fixing holes as they can be wide open into the plenum tunnel?
o Check for other system airleaks
. o brake servo
. o ventilation system reservoir if vacuum operated
. o extra air valve and “U” shaped hose
. o air rail hose from the pipe next to the throttle
. o breather pipe
. o If fitted, air-con valve hoses from its stub pipe to air rail
. o Air supply pipe to the overrun valve if fitted
. o If fitted, vacuum pipe to the automatic transmission
. o AFM to tunnel intake hose
. o Hot spot fixing holes
. o Rocker Cover gaskets not fully sealed - affects air inducted via breather system
o Did you clean and resecure the main Efi Earth Tags to the stud(s) on the block, below and behind the LH rocker cover? The Coolant Temp Sensor uses that tag as its local ground.
o Your sooty spark plugs wont be resolved by fitting new plugs so it does indicate an inherent over-fuelling problem. You will have to consider the reasons why an Efi system overfuels. I'm thinking some of these:
. o Coolant temp sensor or its connections and local engine earth faulty.
. o Fuel pressure too high due to tired pressure regulator or incorrectly setup adjustable version. 36 psi is usually nominal.
. o Blocked air filter.
. o Worn throttle pot electrically noisy causing random overfuelling.
. o Not sure about Air Flow Meter setup on your engine but its a possibility.
. o weeping CSI if fitted.
. o weeping main injector(s) not very likely if all plugs the same.
. o ECU
Not exactly your system, but for oodles of reading material on all of the above: click here
BUT, your flat spot may also have been caused by a faulty throt pot NOT sending ANY acceleration enrichment signals to the ECU because it was not connected properly or the wiper/carbon track were FUBAR.
So - on the horns of a dilemma you gorra try out the new throt pot before moving on.
However, from described symptoms and reported changes you deffo have a lot of work to do, some as as already pointed out. Recap -
o Check ign timing.
o Check vacuum advance by sucking on the vac pipe and listen/watch for the dissy advance function.
o Check dissy mechanical advance - crudely - by visual inspection and turning the rotor arm against the advance springs, ensuring it has resistance and springs back OK.
o Check for disturbed connections.
In Addition
o Did you seal the hotspot fixing holes as they can be wide open into the plenum tunnel?
o Check for other system airleaks
. o brake servo
. o ventilation system reservoir if vacuum operated
. o extra air valve and “U” shaped hose
. o air rail hose from the pipe next to the throttle
. o breather pipe
. o If fitted, air-con valve hoses from its stub pipe to air rail
. o Air supply pipe to the overrun valve if fitted
. o If fitted, vacuum pipe to the automatic transmission
. o AFM to tunnel intake hose
. o Hot spot fixing holes
. o Rocker Cover gaskets not fully sealed - affects air inducted via breather system
o Did you clean and resecure the main Efi Earth Tags to the stud(s) on the block, below and behind the LH rocker cover? The Coolant Temp Sensor uses that tag as its local ground.
o Your sooty spark plugs wont be resolved by fitting new plugs so it does indicate an inherent over-fuelling problem. You will have to consider the reasons why an Efi system overfuels. I'm thinking some of these:
. o Coolant temp sensor or its connections and local engine earth faulty.
. o Fuel pressure too high due to tired pressure regulator or incorrectly setup adjustable version. 36 psi is usually nominal.
. o Blocked air filter.
. o Worn throttle pot electrically noisy causing random overfuelling.
. o Not sure about Air Flow Meter setup on your engine but its a possibility.
. o weeping CSI if fitted.
. o weeping main injector(s) not very likely if all plugs the same.
. o ECU
Not exactly your system, but for oodles of reading material on all of the above: click here
Edited by honestjohntoo on Monday 19th April 00:08
Hi
thanks for the mega reply!
I will check for air leaks etc and give it a run tonight to see if the throttle pot has worked. The 3 wires on the old one all snapped right next to the pot, so i tried to repair by grinding into the pot with the dremel to expose the remaining wire to enable a repair. It did set up at around 340mv but i did seem to get intermittent readings(so perhaps something wasn't quite right)? I will replace the coolant temp sensor as a mater of course (practically replaced everything else!).
thanks for the mega reply!
I will check for air leaks etc and give it a run tonight to see if the throttle pot has worked. The 3 wires on the old one all snapped right next to the pot, so i tried to repair by grinding into the pot with the dremel to expose the remaining wire to enable a repair. It did set up at around 340mv but i did seem to get intermittent readings(so perhaps something wasn't quite right)? I will replace the coolant temp sensor as a mater of course (practically replaced everything else!).
Hi John , whats the out come of your run.
Hopefully all sorted, as i hope to see you and your car at chatsworth (got some strips for your doors)
Not sure this helps you one bit but.............
I 've had a problem with mine since i purchased it (bought it with the classic "needs setting up") thought i would give it some time and miles to see if the problem continued.
The car struggled at 3500rpm ,once through OK .
Then i had a problem with the fuse for the coil, warming up to the point that it melted (first time i 've seen the AA man for my TVR).
So I changed the coil to a orignal, i had as a spare, noticed that the earth cable under the bolt of the coil was rubbish so changed that too, both things were only changed to correct the fuse problem but i also now don't have a car that has a flat spot at 3500rpm.
Hopefully all sorted, as i hope to see you and your car at chatsworth (got some strips for your doors)
Not sure this helps you one bit but.............
I 've had a problem with mine since i purchased it (bought it with the classic "needs setting up") thought i would give it some time and miles to see if the problem continued.
The car struggled at 3500rpm ,once through OK .
Then i had a problem with the fuse for the coil, warming up to the point that it melted (first time i 've seen the AA man for my TVR).
So I changed the coil to a orignal, i had as a spare, noticed that the earth cable under the bolt of the coil was rubbish so changed that too, both things were only changed to correct the fuse problem but i also now don't have a car that has a flat spot at 3500rpm.
Hi
I just managed a quick round the block, so the car didn't warm up properly but it didn't seem too bad. I have ordered a coolant temp sensor as the car appears to be running rich. Either way the car is good to go, hoping to make Chatsworth on Saturday as well so hopefully see you then. Have you still got a picture of the car showing the damage that you could email me?
I just managed a quick round the block, so the car didn't warm up properly but it didn't seem too bad. I have ordered a coolant temp sensor as the car appears to be running rich. Either way the car is good to go, hoping to make Chatsworth on Saturday as well so hopefully see you then. Have you still got a picture of the car showing the damage that you could email me?
Gassing Station | Wedges | Top of Page | What's New | My Stuff