4.5 not liking under 2000rpm

[v8sag]

Just wondering if this is normal. I wouldn't say its hesitant or rough, but the engine doesn't like being under 2000 rpm will driving, it feels like it's just hunting for a little more go at a steady 2000rpm.

Starts and idles beautifully, accelerates like a cut cat, above 2000 rpm holding any rev its fine. Could this just be the map with the short induction installed?

I must admit it's taken me a while to adapt from the Chim 500 and have come to the conclusion; it only likes being driven in one mode, and that's fast. I'll save the city driving for the Chim.

[SimonKD]

Was your car remapped when the short induction was installed? This is critical.

[Byker28i]

The AJP isn't a lazy engine like the rover v8. As standard it's not that happy below 2.5-3k revs as that's where all the torque comes in, 3k as standard. A good mapping sorts it out, or you just drive accordingly and don't try to pull from low revs. Mind you it revs to 8k...

Kits and Classics at Chesterfield is a great place for mapping, probably the recognised best for the MBE

[notaping]

I think it's a fairly common characteristic for the AJP8 to buck slightly at steady low tick over speeds. Mine has done this for most of the time I've owned it - never extreme, but you are aware of it.

It can been tuned out though if you persevere. I managed to get it running very smooth and steady this summer by replacing the throttle pots, changing the throttle link rod ball joints to rose joints (trying to remove as much 'noise' as possible from the throttles) and then recording a series of engine traces and dialing in the mixture settings. It now runs almost like a 'normal' engine at slow constant speeds.

At low engine speed with essentially no load, any changes in fueling reported by the O2 sensors or noisy throttle pots are immediately acted upon by the engine and hence the 'hunting' feeling.

Before second guessing anything though I'd record a series of traces and have a look at what's going on. Look for throttle pot spikes or imbalance between the banks. Check the adaptive values at the 2k range and see if both banks are similar, etc. If you don't feel comfortable with that, take it to a reputable tuner. They should be able to sort it out.

[v8sag]

Thanks for the replies, I think I'm over worrying it. "Bucking" seems an apt word. The annoying thing is, I have a comprehensive history folder from new, besides the obvious physical evidence of the short induction and finding posts from previous owners saying it was mapped too, there's nothing in the file. I'm pretty sure it was also de-catted in NZ, they arrived with the car in the boot, so that could perhaps be contributing to it being a little edgy under/at 2000rpm.

It's having preventive maintenance backlash buckets clearance check soon, so I will ask the engine builder who's looking after it to familiarise himself with the diagnostic software (I have purchased the cable).

The other thing I'll add, I try with city driving to keep a fairly low rpm, any time I back off at over 4000 it's like a fireworks factory explosion out the rear, and considering I used to give tosser's the bird when they gave it the crackle and pops outside my house, I kind of feel like a hypocrite!

Edited by v8sag on Saturday 27th September 08:25

[Byker28i]

Decattng won't affect it. Mine is decatted, which is useful as it reducing the cabin temp and stops the gearbox/clutch/gearchange lever getting hot.
Bad news is the cats quieten the car by 8-10db at 4500-5000 revs.

I usually roll quietly/low revs out my close, even with a quiet exhaust system fitted.

Rolling back from 4000-3000 revs is right on form for pops and bangs on a mapped car You might get flames

[FarmyardPants]

It may be worth checking your earths, eg measure the resistance between the battery -ve, the engine and the chassis. They should be close to zero, obviously. Running a new earth between the engine and battery -ve made my 4.5 run smoother. I can idle along in first gear without any kangarooing, for example

[ridds]

First off, you'll need the relevant cable to connect and the original ECU comms software or the amazing RS-AJP app.

Then I would check:

• Chassis Grounds particularly the one on under the cubby under the radio cubby
• Battery cables and connections to battery terminals
• Coolant Temp Sensor (to the ECU) value
• Exhaust Air Leaks
• Throttle Pots, condition of and setup
• Throttle linkage and return springs on said linkage
• Lambda sensors

Above 2000 revs/min suggests you're using a reasonable amount of throttle, so you would be out of "Lambda Adapted Control" and in "Calculated fueling against TPS and engine speed" mode.

Light Load (small throttle input and / or low engine speed) will mean the ECU / Calibration is in "Closed Loop" for what it's worth, Lambda Adapted Fuel Control and all of the above factors can screw that up. The ECU fuel map has a predetermined fuel delivery target and the Lambda sensor then reads the O2 content of the exhaust gas and the ECU then applies a fuel trim to get said exhaust gas close to a Lambda value of 1.0 ish (14.7 AFR)..

[v8sag]

ridds said:

First off, you'll need the relevant cable to connect and the original ECU comms software or the amazing RS-AJP app.

Then I would check:

• Chassis Grounds particularly the one on under the cubby under the radio cubby
• Battery cables and connections to battery terminals
• Coolant Temp Sensor (to the ECU) value
• Exhaust Air Leaks
• Throttle Pots, condition of and setup
• Throttle linkage and return springs on said linkage
• Lambda sensors

Above 2000 revs/min suggests you're using a reasonable amount of throttle, so you would be out of "Lambda Adapted Control" and in "Calculated fueling against TPS and engine speed" mode.

Light Load (small throttle input and / or low engine speed) will mean the ECU / Calibration is in "Closed Loop" for what it's worth, Lambda Adapted Fuel Control and all of the above factors can screw that up. The ECU fuel map has a predetermined fuel delivery target and the Lambda sensor then reads the O2 content of the exhaust gas and the ECU then applies a fuel trim to get said exhaust gas close to a Lambda value of 1.0 ish (14.7 AFR)..

Thanks so much for the reply and others that have too.

I will have all checked out, hopefully this is the right cable in the pic below

To be honest, I've over committed myself to other TVR projects, so will rely on my automotive engineer and tuner for the diagnostics side of things.
Yep, understand the closed and open loop, I have a 5ltr factory non cat Chim running only open loop, no Lamba(s) and have never ever had any grief, can't say that for the other Chim's I have running them.

Throttle cable play and linkages could be up there, as the "bucking" is only light load and coasting with throttle on/steady.

Besides this small issue the car is running so well and is still in almost the same original condition it left the factory in; it's been so well looked after by previous owners.

While I am here, is there supposed to be a hose off this and if so where to (rear top centre, at the back in the photo)? I presume it's the fuel pressure regulator breather. I still retain my scuttle panel hymen, so thought I'd ask before popping my cherry.

Edited by v8sag on Sunday 5th October 08:55

[v8sag]

Byker28i said:

Decattng won't affect it. Mine is decatted, which is useful as it reducing the cabin temp and stops the gearbox/clutch/gearchange lever getting hot.
Bad news is the cats quieten the car by 8-10db at 4500-5000 revs.

I usually roll quietly/low revs out my close, even with a quiet exhaust system fitted.

Rolling back from 4000-3000 revs is right on form for pops and bangs on a mapped car You might get flames

Had the flames confirmed on a TVR run in the weekend!

[Byker28i]

v8sag said:

Byker28i said:

Decattng won't affect it. Mine is decatted, which is useful as it reducing the cabin temp and stops the gearbox/clutch/gearchange lever getting hot.
Bad news is the cats quieten the car by 8-10db at 4500-5000 revs.

I usually roll quietly/low revs out my close, even with a quiet exhaust system fitted.

Rolling back from 4000-3000 revs is right on form for pops and bangs on a mapped car You might get flames

Had the flames confirmed on a TVR run in the weekend!

[GTi-G60-RB26-RV8-AJPV8]

[quote=v8sag]

While I am here, is there supposed to be a hose off this and if so where to (rear top centre, at the back in the photo)? I presume it's the fuel pressure regulator breather. I still retain my scuttle panel hymen, so thought I'd ask before popping my cherry.

yeah thats just a pressure line that needs to connect to the inlet manifold. helps to adjust fuel flow out of the rail hence rail pressure.

[FarmyardPants]

GTi-G60-RB26-RV8-AJPV8 said:

v8sag said:

While I am here, is there supposed to be a hose off this and if so where to (rear top centre, at the back in the photo)? I presume it's the fuel pressure regulator breather. I still retain my scuttle panel hymen, so thought I'd ask before popping my cherry.

yeah thats just a pressure line that needs to connect to the inlet manifold. helps to adjust fuel flow out of the rail hence rail pressure.

On most cars it is connected to the inlet manifold but on Cerberas it is not connected/reads atmospheric and that’s what the fueling is mapped for.

[GTi-G60-RB26-RV8-AJPV8]

thats good to know!