Dead spot at 4-5k rpm

16th March 2010, 10:03

Spec of the car is:

Raceland inc Green filter
Raceland 4-2-1
Magnex exhaust inc. decat

Freshly serviced inc. Spark plugs, oil, filters, etc.

The car idles nicely (occasional cough & splutter on tickover), but at between 4-5k rpm there is a real dead spot. Not too much of a problem when accelerating up through the gears, but pulling out of corners in third, its almost like a bit of turbo lag, waiting for the 'boost' to kick in at 5k ...

Any suggestions?

16th March 2010, 11:54

Try resetting ECU (batt off for 30mins), might just be the mods versus the oem map. Let it re-learn and it might sort itself out.

Mine does it occasionally.

16th March 2010, 11:57

I think il try this, my vtr sometimes decides to overfuel its tits off.

And then other times not, got piper 4-1, de-cat cat back. viper enclosed induction. Its wierd.

16th March 2010, 12:08

does coil pack not affect this in anyway mate ? can you not burrow one and see if its a coil pack rather than buying one to find that not the problem

16th March 2010, 12:09

I don't think 'resetting' the ECU does jack tbh... it's operating on the same map after all, unless there's a problem that is.

Remove your MAP sensor (on the left-hand side of the inlet mani for VTS, front for VTR) and give it a clean with something like WD40 - gets gunked up with oil over time. Can also do the same with the throttle body etc.

Failing that, I'd probably be looking at changing the pre CAT lambda sensor.

16th March 2010, 12:09

so if i disconect my battery for 30 mins could this stop overfueling? and any dead spots? is it worth a try?

16th March 2010, 12:13

Quote:

Originally Posted by adamm

so if i disconect my battery for 30 mins could this stop overfueling? and any dead spots? is it worth a try?

Won't do anything imo. I'd be looking at renewing your pre-CAT lambda if it's seriously overfuelling - someone I know on here had a duff sensor on his VTR and it was overfuelling to the point of popping flames.

16th March 2010, 12:20

dont think it pops flames. just smells rich or will the straight through decat exhaust be causing this? also my car doesnt seem to do great on mpg

16th March 2010, 12:25

They do stink with a decat - hard to describe the smell... oily-ish?

I'd recommend you do what I suggested sir_dave does - remove your MAP sensor and throttle body and give everything a good clean with WD40/ carb cleaner. Service etc. if needed and check your tyre pressures.

If you don't see any improvement, replace your pre-CAT lambda.

16th March 2010, 12:26

Quote:

Originally Posted by LeeumH

Won't do anything imo. I'd be looking at renewing your pre-CAT lambda if it's seriously overfuelling - someone I know on here had a duff sensor on his VTR and it was overfuelling to the point of popping flames.

Mines at that point.

16th March 2010, 12:27

Quote:

Originally Posted by LeeumH

I don't think 'resetting' the ECU does jack tbh... it's operating on the same map after all, unless there's a problem that is.

Remove your MAP sensor (on the left-hand side of the inlet mani for VTS, front for VTR) and give it a clean with something like WD40 - gets gunked up with oil over time. Can also do the same with the throttle body etc.

Failing that, I'd probably be looking at changing the pre CAT lambda sensor.

Same as what i was going to recommend, MAP sensor

16th March 2010, 12:37

map sensor, is that the grey on that sits ontop of the coilpack infront of the inlet?

16th March 2010, 12:47

If you look where the breather pipe attaches to the inlet manifold, it's just to the left of that... will have a connector going to it. Little 8mm bolt holding it on IIRC.

16th March 2010, 12:54

Not my engine, but is it that one.

16th March 2010, 12:55

Nah that's for the coil pack. Look to the left of the arrow nearest the bottom... see the wires and the connector? The MAP sensor is the little black box that's connected to those wires.

16th March 2010, 12:59

Quote:

Originally Posted by LeeumH

Nah that's for the coil pack. Look to the left of the arrow nearest the bottom... see the wires and the connector? The MAP sensor is the little black box that's connected to those wires.

Muchos grasias.

16th March 2010, 13:01

Quote:

Originally Posted by LeeumH

Remove your MAP sensor (on the left-hand side of the inlet mani for VTS, front for VTR) and give it a clean with something like WD40 - gets gunked up with oil over time. Can also do the same with the throttle body etc.

I'll try that over the next couple of days then!

Cant imagine the ECU needing to be reset again, the batteries been disconnected for about 6 months lol. Will see what benefits cleaning the MAP/throttle body brings ...

16th March 2010, 13:02

Id get it rolling roaded Dave, see what the power actually does at that point in the revs, see if torque dies off, see how bad the AFR's are then go from there, you could end up throwing money at it left right and centre, so with so much info that can be gained from a session id get it on a set of rollers first

16th March 2010, 15:47

Quote:

Originally Posted by sir_dave

I'll try that over the next couple of days then!

Cant imagine the ECU needing to be reset again, the batteries been disconnected for about 6 months lol. Will see what benefits cleaning the MAP/throttle body brings ...

I don't even think there's such a thing as an ECU reset with these cars.

I found it was smoother at low speeds/ pulling away from cold starts etc. I'd be very surprised if you didn't see any improvement doing what I suggested.

17th March 2010, 17:07

Quote:

Originally Posted by LeeumH

I don't even think there's such a thing as an ECU reset with these cars.

I found it was smoother at low speeds/ pulling away from cold starts etc. I'd be very surprised if you didn't see any improvement doing what I suggested.

Its not really a reset, its basically to clear the ECU 'learnt' settings for Air Temp, Air Pressure, Inlet Manifold pressure, lambda readings. It also clears any sensor errors. So if you have a duff coilpack, lambda or MAP resetting the ECU after cleaning em forces it to re-learn the best parameters (which are already pre-defined, or mapped by citroen) to use for the current climate and fuel. Most of the time the MAP will just be dirty so a carb cleaner will sort it in minutes and its only one allen bolt. The lambdas can't be cleaned, there too fragile :/ borrowing a known working one isn't always easy either as they can be a twat to get out.

The parameters are built in so a car in Africa will run like a car in Scotland, in theory.

Ive had problems with the coil pack, MAP and lambdas. Clearing the ECU just helps isolate the problem because a £20 sensor becomes a £60 sensor if you buy the wrong ones. And if you have multiple sensor errors clearing the ECU can give you a more specific idea of whats going on as most of the time it will be one sensor that needs sorting.

20th March 2010, 06:12

Just been thinking about this a little.

How's the car feel from 5-7k?

I'd try and put the oem airbox back on and see how it feels, or just cut some holes in your front slam panel to get some more air into the filter.

Also, having read through some dyno comments at a recent rr day a lot of the standard 16v engines with filters and exhausts were running lean at the top end, so what might be worth trying is putting a 3.5Bar fuel pressure regulator on (standard on 1.4 and 1.6 8v), reset the Ecu and see how it feels 4k+rpm

20th March 2010, 09:09

Surely though as the injectors are set to spray a pre set amount of fuel, upping the fuel pressure wont do anything because the injectors are still only being told to spray a set amount?

20th March 2010, 09:15

I'm pretty sure they don't calculate the fuel going through them.

As far as I'm aware the Ecu tells them how long to open for, increasing the fuel pressure means more fuel is injected in a given milisecond.

Hence if you have injectors running at 80%duty cycle say at 160bhp, you could up the fuel pressure from 3Bar to 4Bar so that they maintain that duty cycle at a power figure roughly 10% above 160bhp.

I'm happy to be corrected but this is as I understand it.

As the lightly modded 16v's were told they were running lean at top end, and 3.5bar fpr's easily got from a lower spec Saxo it'd be worth putting one in to try and richen up the top end as this is where the 16v makes most of it's power.

Admitidly it's crude but should work - beats a £500remap

20th March 2010, 09:21

Your correct in that the ECU does difine how long the injectors stay open for, but from experience i was under the impression that upping the pressure wont increase the amount the injectors can inject, or adjust duty cycle as its all ECU govourned, agaim im happy to be corrected, thats how i understand it

Example is a friend and I have recenty carried out an engine managemnt change on his Sierra XR4x4 twin turbo, and we change the FPR along with it, the old one was running near 5 bar, wear as the new one was set at 3.5, and the amount of fuel being injected was the same, but the uprated pressure from the previous FPR killed the fuel pump lol

Thats now 286bhp on conservative ignition settings, and only 3.5 bar fuel pressure

20th March 2010, 09:34

Was he running standalone engine management though?

But the injectors are surely limited by the length of time they can open on one cycle of an engine? If this is the case then say the max time is 11ms, at a higher fuel pressure more fuel will be injected than a lower pressure?

If I was to put a 3.5Bar fpr in mine (running standalone) then it'd mess my whole fuel map up, whereas I'm sure the oem Ecu (with limited range) can pull or put more fuel in by changing the injectors time based on readings from the lambda - I'd guess that at the top end the Ecu hasn't got the range to put more fuel in hence running a bit lean? I was only suggesting to up the fpr a tad to try and help this out.

What duty cyclue was that sierra running with 5Bar? Now what's it running with 3.5Bar? And it's making the same power?

20th March 2010, 09:47

If you can standalone with 3.5 bar you would have a completely new base map mate, as your fuel map atm is on the base ecu, running stanalone (Omex, Emerald ect) deletes the oem ecu

I can see what your saying, but as far as i was aware, say the injectors open ten times every ms, uprating the pressure to them wont increase fuel as the injectors know the amount of fuel being sent through them, so although they have more to give, they wont as they know the correct amount of fuel is being put through them.

Because if that is incorrect then an injector wouldnt open at, say, 80% fuel cycle, because there is always a little too much fuel pressure in the rail, if they couldnt process the amount they give, then they would always run at 100%? if that makes sense lol

Its making more power with less fuel pressure mate, il grab the details on it later, its back off the road getting a bigger intercooler and exhaust, then back on the rollers (needs more ignition advance, its only 34 degrees on full boost) then hoping for 330bhp and around the same torque. It already hits 0-60 in 4.7secs, so we haoping for low 4s maybe a high 3 on a good day

20th March 2010, 10:03

Just to add,

As far as im aware, as the ecu gets reading from every part of the engine (lambda, air inlet temp,knock sensor etc) then it can make small base map adjustments due to air temp, fuel RON, etc.

So lets say injectors run at 80% duty, if an uprated filter is fitted and it is now flowing more air, it can adjust the amount of fuel being injected accordingly to account for the extra air coming in by opening the injector earlier or by increasing the duty slightly.

If increasing fuel pressure, the engine still reads the amount of fuel going in, so lets say the physical amount of fuel going in is now more than the required amount, the ecu will trim off the duty, to compensate for the extra going in.

I would have though that the ecu would be able to compensate for the smaller changes, but the higher bhp lads (160+) would need more fuel, so a tweak of the fuel map adjusting the fuel perameters would open injectors more, giving the added fuel

Although as said im happy to be shown otherwise, always eager to learn more if iv been taught wrong

Oh and Dave, id def say get it on the rollers mate, as you can see AFR's and see if it is lean

20th March 2010, 10:36

Quote:

Originally Posted by Russ_16v

Just to add,

As far as im aware, as the ecu gets reading from every part of the engine (lambda, air inlet temp,knock sensor etc) then it can make small base map adjustments due to air temp, fuel RON, etc.

So lets say injectors run at 80% duty, if an uprated filter is fitted and it is now flowing more air, it can adjust the amount of fuel being injected accordingly to account for the extra air coming in by opening the injector earlier or by increasing the duty slightly.

If increasing fuel pressure, the engine still reads the amount of fuel going in, so lets say the physical amount of fuel going in is now more than the required amount, the ecu will trim off the duty, to compensate for the extra going in.

I would have though that the ecu would be able to compensate for the smaller changes, but the higher bhp lads (160+) would need more fuel, so a tweak of the fuel map adjusting the fuel perameters would open injectors more, giving the added fuel

Although as said im happy to be shown otherwise, always eager to learn more if iv been taught wrong

Oh and Dave, id def say get it on the rollers mate, as you can see AFR's and see if it is lean

I agree with that 100%, the rollers would tell you what the afr was doing and power wise through the revs

Another question worth asking is at what point does the Ecu switch from an open loop lambda setup to closed loop? - I remember reading (can't remember if its off here or ssc) that the 16v Ecu switches to a closed loop lambda setup over like 4k and 70% TPS (or something along those lines - can't remember the figures off the top of my head or whether its a MAP amount). The Ecu will then be purely reading the fueling from a map, which case it would benefit from a slight increase in fuel pressure if it's running lean? It might be running spot which case the flat spot is something else.

Here's the thread about the running lean at top end stuff (about half way down):
http://www.saxperience.com/forum/sho...37#post4209437

getting back on topic

For the OP, I'd loot to get better airflow to the raceland setup and go from there if the flatspot is still there.

20th March 2010, 10:49

You should see the AFR's for my 172, standard REnault map, only with an exhaust fitted, they are shocking!! Runs down to 11 at one point, then over 14 at another!!

A custom map will do any engine good in my opinion, especially after seeing my graph!

Also a generic map i dont like, a good exammple is a friend has a 306 GTi-6, and had a filter and exhaust setup and was recommended by a reputable chip company to buy a generic chip to help with the mods.

Well once on the rollers it hit a wall at 6800rpm and dropped so lean it was dangerous! My mapper aborted the run and said take it back,so just a word of warning there

Ah that is a good point mate, a restriction in airflow could cause it

20th April 2010, 17:01

Just to let people know, this issue seems to have cured itself after thrashing it around for 500 miles or so ... think Llandow cleared its lungs out a bit as well tbh. After all, it had been sat unused for 9 months!!

Either that, or the Saxsport has mythical powers

Essentially it now pulls beautifully from idle all the way up to the redline. Brilliant