Fuel consumption too high.

Level 1 User Joined: 22 Apr 2004 Posts: 34

Hi.
My Ren has used too much fuel (petrol?, gas?) since the engine swap. The swap was E7J to E7J. The consumption is about 35mpg (8l/100km). Doesn't really matter how or where I drive. With the old engine I was able to achieve 47mpg (6l/100km) when driving nicely. Just before the engine swap I replaced the lambda. Am I looking at a crappy lambda (or it's wiring) or could it be something else?

The wiring of the R19 is crap. I'll change the sensor wirings some day. Is it easy to spot where the wires should go in the engine management box?

When the air is cold and moist and starting with a cold engine, the engine stalls sometimes a bit but that disappears quite fast. Might have nothing to do with the consumption...

And if I put the rear window heater on, the engine practically dies. That's not nice in the wintertime. Evil or Very Mad

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

well if it dies when you switch on the rear window then the stepper motors playing up.

If you look on the tech articles section of the forums I done a recent guide on th SPI throttle body. Follow that.

Coolant temp sensor is always a possibilty, these at best last 10 years, more if the cooling system is looked after but this is rare tbh.

Did you fit a speedo cable with the road speed sensor in it and did the dash have the connector for the wiring plug?

Level 1 User Joined: 22 Apr 2004 Posts: 34

Hi Chris.

Why would the widow heater f*ck up the idle stepper motor? I'd like to know before I jump into disassemblying it.

With the engine swap I tested all the sensors with an ohmmeter (temp sensors cold & hot). And the cooling temp sensors and cooling temp light switches looked good (got double of them because the engine had them mounted).

The speedo cable in this one is and has been merely a cable. No road speed sensing stuff for the ECU.

I've cleaned the TB (not disassebled the fuel pressure regulator or the idle motor) - many times.

I was thinking about the lambda as the reason since before the engine swap the 3rd cylinder was very low in compression -> fuel didn't burn properly -> the lambda obviously sent a message and the ECU turned the micture to leaner (which now is soooo obvious considering the symptoms - wasn't then Sad

). But I swapped the lambda because failure in mot and the next failure made me swap the cat and the engine. The old kat wasn't blown into tube, it looked quite clogged. So I don't suspect the new kat.

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

the extra load on the engine when you switch the HRW on or head lights etc etc should be compesated for by the idle stepper motor, when they are sticky they don't respond quickly or accurately enough.

It needs road speed sensing signal for the ECU to know the cars in motion and to prevent stalling pulling up to junctions etc. It also affects the idle. But if its not there an never has been since its been installed it should have learned to ignore this, although it will run better with the right signal. Indeed it may solve all the trouble.

But you also look at the MAP sensor etc, if theres a leak in its pipe it will think its under full load thus throw in more fuel.

Ohmeter testing isnt good enough for the sender, they can fail but still be in operating tolerences, they may read fine up to 80 degrees but at 82 degrees the sensor may tell the ECU the engine has just dropped to 0 degrees. The ECU is not clever enough to realise this is false.

Lambda etc, only way to tell is to get an emmisions test but I would think its ok.

Level 1 User Joined: 22 Apr 2004 Posts: 34

Chris, you puzzle me.

I thought that there were models with and without the road speed sensor (ref. Haynes). And no, there wasn't any connectors left for a wiring plug if you mean the backside of the speed&rev&warning light&etc. panel's backside.

Isn't the engine speed/pos sensor signal enough for the ECU then?

There aren't vacuum leaks unless the MAP is busted. I've renewed all hoses and seals. The brake assistant I clamped to see if the vacuum cylinder leaked. It didn't.

I still can't see how the *idle* stepper motor (ISM) would affect the engine's running when I'm, let's say pulling off from lights. Everything is nice and I'm speeding up until I switch the HRW on. Power gone. Switch it off and here we go again. Oh, and the HRW doesn't affect idle noticeably.

What would happen if I pull the plug on ISM and try switching on then.... Maybe I'll just have to try that to narrow down the possibilities.

I'll have to run the engine *hot* and check the temp sensor then too.

Could a MAP with a broken or stretched diaphram cause something like this?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

Don't worry I puzzle myself as well.

Yes the back of the panel.

The injection models all had road speed sensors, the ECU needs that input.

The carbed models are th eonly models without the speedo sensor.

The plug is where the dash display goes in, if the plug hasn't been used then its wrapped up in a bit of foam, dig around and it should be in there.

All dashes from 92 on had them.

The engine speed and load signal are enough for the engine to run but the road speed input prevents stalling etc on over run shut off. Basically over run shut off happens down to around 1500rpm then the injectors coem back to prevent the thing stalling etc.

Your right the idle solenoid shouldn't affect ou pulling away from lights unless your using very little throttle then it will.

So what your saying is when on the move switchign the HRW on the power goes but its ok at idle etc?

Unplugging the idle control plug will make the engine rev up to nearly 2krpm, maybe more depending and not deviate.

but if the cars fine when driving and only has trouble when you turn the HRW on I'd say alts either playing up or an earth. The HRW is earthed on the back panel under the rear lights as is the fuel pump.

So dodgy earth there when the HRW will make the pump slow causing a loss in power, might not be that but worth a look.

Level 1 User Joined: 22 Apr 2004 Posts: 34

Hi Chris and thanks.

Quote:

Your right the idle solenoid shouldn't affect ou pulling away from lights unless your using very little throttle then it will.

Like I would do that. Embarassed

Yes, the idle doesn't care much if the HRW is on - it may rev a little slower but no prob. But if I'm driving even if 4000rpm, the HRW will make the car slow down. Can't remember how it behaves when I floor it with the HRW on. This is why I use it while I'm using the engine to slow down (no throttle of course) or I've stopped in lights or for some other reason.

Something I forgot to mention... the HRW won't screw up driving in couple of minutes after I start a cold engine.

The road speed sensor puzzles me since there was somekind of plug... don't remeber the material thou. But if there's a plugged hole and this car has always had a '91 SPI system - that shouldn't be. Should it?

What would a cable with the road speed sensor cost? About?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

the HRW beign fine when the cars cold leads me to suspect its a wiring/connector/earth problem.

After all resistance increases with temp so when cold the connection might be ok resistance wise but as it gets used by the HRW and pump and lights etc the connection heats up and reistance goes up with it slowing the pump.

Road speed senosr is a white plug, long and thin.

Speedo is 70quid + VAT from ren but any 19/clio injection cable should do the job. the clio cable fits but it can be a bit tight on some cars.

Level 1 User Joined: 22 Apr 2004 Posts: 34

Hi Chris.
What a rip off from Ren. I'll try to find a better deal from somewhere else.

I guess I just have to track down that wiring/connector/earth problem then to get HRW available.

Thanks Chris. You've been very helpful, once again.

Edit: Will the road speed sensor affect consumption?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

it CAN affect consumption but it might not in this case. But i'd imagine that it would improve matters but I can't say for 100%.