Engine idle issue on 350i

[keynsham]

I have just rebuilt my engine with a new camshaft (TVR51, 4 litre) and replaced head gaskets, timing gear etc. I took the inlet manifold offocomplete and didn't take it apart at all as I have done that previously. It is all back together now but it will not idle. It was very difficult to start, a bit like trying to start a car with no choke. When eventually coaxed into life it will rev and seems happy but as soon as I take my foot off the throttle it is as if the fuel has been turned off and it just stops. I can catch it if I jump up and down on the throttle. It will run at 1000rpm with thottle pedal assistance but otherwise not. I suspect as I haven't really changed anything significantly and all sensors were OK before, that I may have damaged a wire when bending the loom about.

So far I have checked to see if the cold start injector does anything and it doesn't but the engine was warming up by then and I am not sure how long that works for?

Anyone got any suggestions as to where to start diagnosing the issue?

[KKson]

Did you double check you wired correctly back the coolant temperature sensor and thermotime switch? Same connector on both and right next to each other.

[BlueWedgy]

might want to double-check head block earths as well.
Could also have a air leak somewhere.

Edited by BlueWedgy on Thursday 10th August 12:38

[keynsham]

I have checked and double checked all wiring and joints, pipes and anything else. It is all as the photos I took before I took it apart. All I have changed are the HT leads and the camshaft. If I manage to start it, it will rev but dies as soon as you lift off the throttle. I have worked out that when it is very cold, the cold start injector allows it to initially fire. I can then sometimes catch it with the throttle. the Auxiliary Air valve is operating ok, but it seems the 'message' to inject more fuel when the airflow is increased via the AAV isn't getting through to the ECU. As I said, it acts just like a cold engine in a car with a choke when you don't have the choke out.

It is very frustrating as I can usually find something wrong, but this has me foxed for the moment!!

[mk1fan]

Does it run if you squirt 'easy start' into the engine via one of the vacumm hoses [two man job]? Then at least you know it is fuel related.

[blaze_away]

Those symptoms describe classic vacuum leak. At idle the butterfly is shut and plenum is at its highest vacuum ergo vacuum leak occurs, then as soon as ypu touch the throttle butterfly opens vacuum collapses and leak aubstantially drops.

Best and most effecyove way to detect and fix is a smoke generator shoved into the plenum inlet hose.

[keynsham]

Actually, when I press the throttle quickly, when I have managed to get it started, there is a loud 'sucking' noise just as the engine begins to rev which seems to come from the throttle flap area of the plenum. I have never noticed it before but it could be a leak. I will have a really good check later to see if there is anything wrong there.

[blaze_away]

On my Chim under the butterfly area are 2 heater pipes attached to a plate. Under the plate is a gasket that separayes water from air inlet. Mine was leaking there. Note the heater pipes arent connected to anything sp air was being sucked in via the pipes and through the crappy gasket.

[BlueWedgy]

Definitely sounds like an air leak around the Plenun / Air meter area.
Out of interest can you please confirm the cam spec and engine size fitted to?

[keynsham]

It is a standard 350i so Rover SD1 Vitesse except for a Kent TVR51 camshaft which is the standard 4 litre spec cam.

[BlueWedgy]

Oh thats an interesting choice, I was looking at a 3.9.
I have read that some cams have increased lift, which could cause the valves to hit the standard piston?

[keynsham]

I think the 3.9 cam is standard in the vitesse engine anyway. The Kent TVR51 was recommended to me by TVRSSW who fit them to all 350i's. I has a lift of 0.4" compared to the 0.39" of the standard cam and needs no other engine mods. As my old cam was evenly worn to giving a lift of 0.37", I suspect I may notice some difference!

[keynsham]

So having checked everything I am beginning to think it is me! I have assumed, based on advice I have been given, that the TVR51 camshaft is a drop in fit with no other work needed. One thing I haven't touched since I rebuilt the engine however is the idle screw. If the new cam required a different idle setting then maybe not enough air is getting through the idle screw and therefore not enough fuel. It would certainly answer all my running issues!

So my question for those who have changed camshafts... does it mess with the idle setting?

[BlueWedgy]

It is my understanding, and it is just that really. If the cam fitted has a longer duration, then this will affect idle speed, and therefore running, the iddle becomes lumpy so will need more idle speed to be smoother.
Perhaps drop TVRSSW a line and see if they can throw some light on it.

[keynsham]

So, after all of that, it seems it was all operator error! I just turned the idle screw out two turns and the engine is fully recovered, tick over and all!! I overlooked this because I was told the camshaft was just a drop in and 'no other alterations or modifications' were needed. I think I took that too literally and assumed all settings should also be the same. Lesson learnt! I will check the exhaust with a CO meter and set the idle mixture as it is a little lumpy at the moment, but apart from that problem sorted without spending any money!!!!

Looking forward to getting out for a blast ASAP, assuming thew rain stops.

Thanks for all the help and comments. Forums are great places.

[BlueWedgy]

That's good well done. I would be interested when you do get out if there Is a perceived change?
I think that there will be an increase in torque lower down with little or not much of a change at the top end perhaps.

[keynsham]

Well actually, I discovered afterwards that the idle was not really the main issue, but the timing. When the timing is set per instructions, 8 deg BTDC static and rotor arm pointing to N0l.1 lead, the car will not start. Having doen a bit of fittling, I discovered that as I turn the distributor ACW, the engine suddenly runs and becomes very happy. I have positioned No.1 piston ad TDC and found my timing marks to read 5 deg ATDC! So the timing marks on the front pulley are basically way out! I have marked the correct TDC on the pulley now and I will set the timing using a strobe light tomorrow to get it right.

TVR's are full of surprises but I do enjoy a good challenge!! It's only an engine after all!

[keynsham]

So my engine is now sorted. Starts and runs as it should. The issues I had were very difficult starting and no idle after a rebuild.

The problems were firstly that the TDC mark on my crankshaft pulley is actually at 5 deg ATDC so setting the static timing at 8 deg BTDC was actually 13 deg BTDC. Secondly, when I set the static timing, I set the crankshaft position to what I thought was 8 deg BTDC and then rotated the distributor cap to align the rotor arm with No.1 lead. However the book doesn't tell you to do this but rather to position the ferrite rod in relation to the pick-up inside the distributor. Once these two things were sorted, it is all now good!

And on a better note still, I initially took my engine apart because of a suspected head gasket issue that was pressurising the cooling system and blowing all the coolant out of the expansion and overflow tank. This is now sorted!

Back on the road to enjoy the sun again at last!!

[keynsham]

Well that was sdhort lived! 35 miles later and the fan has decided to part company with the motor by somehow splitting and melting the plastic boss in the fan itself, and it ultimately overheated.

I have to say my wedge is certainly doing all it can to uphold TVR's reputation for reliability!!

[BlueWedgy]

Funnily, mine lurches from one thing to another as well.
I seem to spend more time doing stuff than driving the thing.

Although this time it was me needing repair lol.

It must be all that extra power you have unleashed?