Renault 21 non hot starting

[düdo]

Evening all, I am hoping someone can shed some light on my issues which have stumped me despite best efforts..

I've just put a 'new' motor in my 1988 R21 - it's a 1.7 multi-point injected F3N petrol.

It starts and runs but idles around 1500 rpm. As it warms up the idle increases til it eventually it stalls around 2500 rpm. I then can't start it for approx twenty mins.

My efforts so far :

- checked for vacuum leaks.
- replaced temp sensor in the block
- replaced idle control valve and throttle control valve. Used but supposedly good
- swapped used ECU

Injectors are reconditioned, fuel pump is new. Once it's stalled there's still spark at the distributor which is also new. I haven't checked to see if the injectors are spraying after it stalls but there fuel pressure on the rail

Any ideas greatly appreciated as I'm a bit stuck. Maybe someone has had similar symptons? Thanks a lot

[vitesseefi]

Does it answer the throttle and could you keep it going if kept it revving higher with the throttle open?

Pretty sure it will be a vacuum leak somewhere.

Reasoning being that the engine must have air to run and an unloaded engine doesn't need much air to run quite fast. I'm wondering if it'll run when coldish because the ECU is adding fuel making it rich enough to run but as it warms up the ECU backs off the fuel until the extra air makes it too lean to run any more?

My brother had issues with his 1.7 carb fed R21 which would idle very lumpily and slowly on 3 cylinders except when it was on choke when it would idle faster than usual and on 4 cylinders. At higher loads and rpms it was almost normal. We eventually compression tested it (by chance with the throttle closed) and got 1 cylinder with more compression than the others and it dawned on us that it had an airleak at the gasket where the manifold joins the head. There was a little piece gone on just one cylinder (the one with the higher reading), at the bottom where it was impossible to even spray carb cleaner. New gasket solved the problem.

Nick

[düdo]

Thanks for the answer Nick. That gets me thinking.

I sprayed the whole induction area with carb cleaner looking for a leak but I actually just thought that the manifold blew a little smoke when it started again. The in/outlet share a gasket. I swapped manifolds and used a new gasket but maybe I didn't get it tight enough?

It's become like a game of chess. Me v R21 Nevada

[ChasR]

I would have also thought it's a vacuum leak as well.

[ettorebugatti]

TDC sensor can go faulty on the Renix controlled engines. As the ground loop/earth to the engine.

But vacuum leak sounds like a main contributor.

[MonzaPhil]

I seem to recall them warping inlet manifolds leading to this sort of thing.

[düdo]

Sept 20, 2016 13:48:42 GMT MonzaPhil said:

I seem to recall them warping inlet manifolds leading to this sort of thing.

That's another interesting idea. Thankyou. I had to use the inlet and exhaust manifold from the old engine as they fitted together and the exhaust manifold has the lambda sensor fitted there rather than at the cat which the 'new' motor would have had. The previous engine had been cooked so maybe the manifold got it as well?

Tightened the manifold studs today and the first one sheared so spent my limited time taking it all apart again and trying to drill and pull the stud remnants without any luck. Trying to drill a stud that you can't really see upside down using a mirror isn't recommended. Would have got it on the bench but I really can't take the whole motor out again. It's the furthermost outside stud closest to an exhaust port. I'm sorry to say I Hylomared it and put it all back together, closed the door of the barn and went home. Lonesome cowboy Joe. Well, Rolls Royce apparently used Hylomar to seal the flanges in gas turbine engines. Maybe I should slap some on the intake manifold too? And squirt the rest up my nose! 

[georgeb]

Sept 20, 2016 13:48:42 GMT MonzaPhil said:

I seem to recall them warping inlet manifolds leading to this sort of thing.

That was my first thought.

Many years ago, I worked for a Renault dealer and was heading home in a px 21 Turbo. Just for the crack, I set the cruise control for the Heart of the Sun and about 2 minutes later, the bloody thing ran away with me, accelerating hard where I didn't want it to.

Whizzed it into the mechanics the next morning and that's what had happened. Manifold warped.

Sold it to a policeman friend of mine on the grounds that if it happened again, he'd get away with it

[düdo]

Sept 23, 2016 7:07:08 GMT georgeb said:

Sept 20, 2016 13:48:42 GMT MonzaPhil said:

I seem to recall them warping inlet manifolds leading to this sort of thing.

That was my first thought.

Many years ago, I worked for a Renault dealer and was heading home in a px 21 Turbo. Just for the crack, I set the cruise control for the Heart of the Sun and about 2 minutes later, the bloody thing ran away with me, accelerating hard where I didn't want it to.

Whizzed it into the mechanics the next morning and that's what had happened. Manifold warped.

Sold it to a policeman friend of mine on the grounds that if it happened again, he'd get away with it

Thanks George. It does appear to be a warped manifold.

I want to fit the second manifold and try it but the broken stud in the engine block mentioned above has turned into a real nightmare. I got a drill on it eventually and it started turning clockwise, further into the head. So I figured that a left turning drill would draw it out. Problem is that no one has heard of such things here and I ended up with a left turning bit shaped like a christmas tree which of course broke off in the hole that I had drilled in the stud. Attempts to drill it have just made a right dog's dinner of the hole. So I'm stuck.

I'm thinking that I might have to take the engine out again and helicoil it?

Or there's another threaded hole in the block above the one that I've stuffed. I'm wondering if I weld a small extension onto the manifold if I can use that?

[düdo]

The pain continues...


I've amended the title as the runaway idle is now sorted - I'd got a couple of the vacuum hoses wrongly connected. But the hot non starting continues. The diagnostic machine indicates a sudden temp leap from 60° to 160° as the engine heats up. Obviously a false reading but can't tell the management system that and the engine won't start

It has been in a local workshop with Englebert for over a month and he can't crack it.

- all sensors and cables to them have been tested
- the ECU went to a pro to be tested and came back with no problems indicated

Englebert wants to send it to another technician for testing for second opinion as he's convinced that he can only be the ECU. The workshop they sent it to is very reputable and I have used them before so I'm not convinced..

Any ideas appreciated no matter how bizarre.. 'maybe because it's an old French heap' I already know!

Thankyou

[vitesseefi]

It's an old French heap...... They are a special kind of awkward!

Have you considered the possibility that the temperature sensor may not be the correct one and has a different resistance/temperature profile relative to what the ECU is configured for?

Nick

[düdo]

That's a good shout vitesseefi thanks.. I was circling that area and actually had got the wrong sensor installed which was corrected by Englebert. Didn't change anything. Or perhaps he's got the wrong one too? Or there's some continuity issue there? But they checked everything.. he gets his gimp/apprentice to work on it as experience in French mind-fcuks. I think it's starting to do Engleberts's head in too! Have a Pernod my dear..

Will send the ECU for second opinion then I reckon it's back to detailed circuit testing. It's frustrating that it's now got TÜV/MoT for the first time in fifteen years but is undriveable. Maybe I'll have a Pernod.. leave the bottle here garcon.

[nomad]

I've got no Renault experience but painful lessons from years ago :
 Nissan 200SX S13. "new" engine kept hunting at tickover, finally found identified that the TPS (throttle position sensor) on the new engine looked identical to the old engine but had different but gave different resistance which confused the ECU. Maybe fit all the old sensors to the new engine and try that ? or check resistance on each with a basic multimeter to check they are the same?
 Citroen Xsara. It's French. They hate us! ( there were only 4 colours in the wiring harness making fault-finding "fun", and the speedo binacle needed to be removed to swap the brake light switch. Rumour has it this only applies to UK models!)

Hope you get it sorted, expect it to be simple to fix - once you've found the problem.

[düdo]

Thanks for the ideas nomad.. it's a never-ending palavar

R21 still with Engelbert who has sent the ECU to another specialist. It's a load of sweat for a worthless piece of 'ancienne merde' ( bad translation of ye olde wibblepoo) but we persevere..

[ChasR]

I was going to ask about the resistance readings that the ECU sensor gives at verying temperatures and whether it runs without it.

[düdo]

Dec 1, 2016 23:36:59 GMT ChasR said:

I was going to ask about the resistance readings that the ECU sensor gives at verying temperatures and whether it runs without it.

Thanks for the reply. Are you referring to the temp sensor?

There was the idea to put a resistor in line to the temp sensor so the ECU always thinks the engine's cold but Engelbert sent the ECU to the second specialist who found a fault of some description. It's arriving back tomorrow so we try again..