Any ideas whats causing this

[Richie-Van-GTi 74 2 Cars]

Car idles great at 14.6-14.7 afr, above 3k its great, from 2-3 k its very hesitant, misfiring and generally embarrassing to be near.

Spark plugs are all black on one side only.

Its been on the rollers 3 times and they cant find anything wrong with timing or fueling. Its now had coil pack, leads, ignition amp, injectors and plugs. Fpr is new and pressure has been tested etc.

Driving me crazy as I just want to drive it.

1.6 8v gti, 11:1 CR, piper 275 cam, 4 branch manifold, 60/2 billet flywheel, adaptronic E420 ecu, map sensor, throttle potentiometer, 200cc injectors, wideband lambda and mapped as map vs rpm

Edited March 21 by Richie-Van-GTi

[Thijs_Rallye 89 4 Cars]

Is it hesitant between 2k and 3k @ wot? Or part throttle? Did they only map the high load cells or also the "zero" load cells in the calibration? Does it run open or closed loop in that part? There are a lot of factors in play, especially with a cammed engine. Cammed engines and map sensors do not always play nice afaik.

 

Looking at the plugs it appears to run pig rich. What heat range are they?

[Richie-Van-GTi 74 2 Cars]

49 minutes ago, Thijs_Rallye said:

Is it hesitant between 2k and 3k @ wot? Or part throttle? Did they only map the high load cells or also the "zero" load cells in the calibration? Does it run open or closed loop in that part? There are a lot of factors in play, especially with a cammed engine. Cammed engines and map sensors do not always play nice afaik.

 

Looking at the plugs it appears to run pig rich. What heat range are they?

Hesitant at any throttle range other than steady rpm, all open loop, not been able to get it running well enough to test closed loop. Map readings look fairly steady throughout the range.

Plugs are ngk bcpr6es, tried 7s as well

[petert 608]

So hard to diagnose from the bus I’m on, but first thing I’d do is make it idle at 13 to 13.5.

[petert 608]

Are you sure the wideband is correct? Idling an engine with a bigger cam at 14.7 seems foreign to me.

[Richie-Van-GTi 74 2 Cars]

9 hours ago, petert said:

So hard to diagnose from the bus I’m on, but first thing I’d do is make it idle at 13 to 13.5.

Sounds very rich for idle, would expect that at high rpm.

9 hours ago, petert said:

Are you sure the wideband is correct? Idling an engine with a bigger cam at 14.7 seems foreign to me.

Yes wideband is correct, he tested everything and validated the figures with his standalone equipment while mapping.

Only parts that weren't reliable were knock sensor which is not being used now and the idle control (mi16 pwm type) which is now converted back to a standard SAD system.

[petert 608]

Idle AFR can be difficult if you don't have a sensor in the oem position, as there isn't enough flow. How did you set the idle AFR? Is there a zero throttle map, which overrides the MAP sensor?

[Richie-Van-GTi 74 2 Cars]

No override, it just uses map vs rpm throughout. Idle isnt an issue though, its just the 2k to 3k rpm range

[Richie-Van-GTi 74 2 Cars]

I did wonder if its the FPR, maybe its pulsing the fuel pressure in that range and would it be better to remove the vac hose on it and just have one pressure throughout? Not sure exactly how they behave normally, I would expect a smooth transition but at what throttle/map range?

[welshpug 1,677]

that may well be an useful place to start, remove any possible variance, is it a fixed FPR bar the vacuum reference?

 

rather odd to be mapping a lumpy cam engine on MAP, typically it would be on TPS if there's chance of uneven or large pulses.

 

this is where your money pays to find a good mapper.

[Thijs_Rallye 89 4 Cars]

3 hours ago, Richie-Van-GTi said:

I did wonder if its the FPR, maybe its pulsing the fuel pressure in that range and would it be better to remove the vac hose on it and just have one pressure throughout? Not sure exactly how they behave normally, I would expect a smooth transition but at what throttle/map range?

I would expect the map sensor to swing even wilder than your fuel pressure because of the intake pulsing. Did they use a separate vacuum gauge during the rolling road mapping session? I wouldn't be surprised if it's harmonics that are ruining the map signal. 

 

Like Peter says, some ECU's have the possibility to run a different load strategy at certain operating points / areas. Or maybe it supports signal conditioning at those areas. That could be a solution if it are the harmonics in the intake.

 

Is the map fitted directly in the plenum or is the vacuum routed to the sensor with a hose? Might be worth a try as well to "throttle"/pinch the hose to hopefully smooth the vacuum signal as a test. 

 

It's all mostly guess work from my side here though, hard to tell without having hands on the vehicle.  

 

[SRDT 199]

When using MAP wit ITBs you need a small plenum to get rid of pulses and I think some OEM have something simimiar on the vacuum hose when the MAP sensor is inside the ECU.

[Richie-Van-GTi 74 2 Cars]

Map sensor is remote on a thin vac pipe, about 4mm ID I think from memory, standard plenum and throttle body but a potentiometer rather than the old school switch.

Its quite an old adaptronic ecu so it doesnt have a load of extra functions for splitting the mapping across the loads etc, its one map or the other. It could be mapped as TPS/rpm rather than map sensor but want to be sure that is the issue first, 2 different mappers have had it and neither commented on the map signal being an issue.

[welshpug 1,677]

Remote mounting the map sensor is fine and not uncommon,  but you do need a firm rubber hose for it, thin silicone is not very stiff.

 

You can also fit a damper inline, zx and 405 used them.

[Richie-Van-GTi 74 2 Cars]

1 hour ago, welshpug said:

Remote mounting the map sensor is fine and not uncommon,  but you do need a firm rubber hose for it, thin silicone is not very stiff.

 

You can also fit a damper inline, zx and 405 used them.

Its a good quality vac line, not soft silicon, quite firm braided pipe.

Will have a look for the damper, thanks

[Richie-Van-GTi 74 2 Cars]

A quick update, saturday the problem developed significantly and had to come home behind an orange chariot known as the RAC.

It felt like the coil was just turning off and on when the car was under load so I suspected a break in the wiring somewhere.

Spent sunday renewing all the earth straps and main live wires, also switched 3 relays that control my fuel, coil, injectors and idle control.

 

Car now seems to be driving perfectly.

[Telf 232 2 Cars]

I might be getting the wrong idea here but my 8v is running just off the throttle sensor potentiometer. I'm on an Emerald ECU. I originally wired a map sensor in and its still fitted but unused, when I took the car to Emerald they disabled it and said it would be mapped just on the throttle sensor and Lambda reading.

 

It's just an 8v on the standard throttle body and plenum intake.

 

So why do you use a map sensor and TPS?

[Tom Fenton 1,562]

On 3/21/2025 at 6:18 PM, Richie-Van-GTi said:

 

1.6 8v gti, 11:1 CR, piper 275 cam, 4 branch manifold, 60/2 billet flywheel, adaptronic E420 ecu, map sensor, throttle potentiometer, 200cc injectors, wideband lambda and mapped as map vs rpm

 

By no means an expert, but this spec cam compression says to me it would be much better suited to being mapped using TPS as main load reference.

[SRDT 199]

On 4/8/2025 at 8:59 PM, Telf said:

they disabled it and said it would be mapped just on the throttle sensor and Lambda reading.

TPS + lambda is much better than TPS alone. Some early single point injection systems ran like that.

To be really as good as TPS + MAP you need a more accurate TPS at small openings, also any problem with the lambda signal will make it run poorly.

[petert 608]

Blending MAP and TPS is much better than either alone. You need at least one MAP sensor to compensate for altitude correction.