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Discussion Starter · #1 ·
Hi Everybody

The problem: as title.
The car:

1991 CS 2.3T
Manual
130,000 miles


Recently I had been having misfiring and boost problems which have subsequently now been repaired. It turned out that the DI cassette was on its way out.

Anyway, during this time I was experiencing bad fuel economy, 22 mpg(calculated from completely brimmed full tank to full tank, not from the EDU).
As I knew the car had a ignition problem I put the bad fuel economy down to that. However, the car is now driving very well, good performance, smooth power delivery etc.

The car also had its MOT recently and the exhaust emissions were all well within normal.

I have no 'check engine' light coming on.

When I first got this car about a year ago I was getting about 28-32 mpg which I was happy with as it was a little better than my last 2.3T

But, this car will not give better than about 22mpg, and I have been driving it with fuel economy in mind.

The car also idles smoothly at about 850-900 rpm. So, I guess i can rule out a dirty AIC.

I have done several searches on saabscene to see if there are any other similar posts but the ones that i find also have other symptoms which i am not getting.

Car was recently serviced. Plugs, air filter, oil filter, oil. The service has not helped with the poor fuel economy.

I have read about faulty lambda sensors giving poor fuel economy but it is 22 mpg not 10mpg which i gather is about the norm for a failed lambda sensor.

Any adice you guys can give me would be gratefully received.

Cheers

9k

Sorry about the long post but thanks for taking the time to read it.
 

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not much comfort i guess but my'96 2.3 lpt only does about your average. upto 28 on long runs,and down to 18 around town.it is an auto but even so....ive asked about this at services questioning fuel filters,plugs etc etc and come up blank. guess its just an alcoholic!
 

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Last August purchased my first 98' 9000 Auto 2.3T with 138,000mi it got 24mpg since Winter I average 20.5mpg and noticed 6 weeks ago temp pseudo gauge, dial bounces around 37-45percent of full sweep. The thermostat is 10,000mi old and I suspect this my be my problem??? Low temp signal from sendor to ECM will give a rich mixture therefore a lower fuel economy.
If temp sendor"s" not sure as to how many, they deteriorate with age, this also can count for poor fuel economy. I had a 84'Chevy that had 4 temp sendors on thermostat housing and more on block and head, it seem like a conglomerated average of signals put in a catagorized spectrum to be analized by the ECM . Also you have on Saab
(2)oxy, air, map and other sendor signals that make up for good fuel economy. You might have one two or possibly three bad signals working intermittently.
Good luck!
 

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Discussion Starter · #4 ·
k9saab. Sorry to hear you have got pretty poor fuel economy too. I am determined to get to the bottom of this though. When/if I ever do I will re-post here and maybe something will help you and others.

Saabitall9000: Thanks for the info. I will look into temperature senders etc. In the UK with our crazy fuel prices (@ £0.80 per litre) this 22 mpg is really bothering me when I know it could be better.

Something that I did notice was that that, all of a sudden, the fuel economy bar (sorry, not sure the correct term for this 'on the fly' gauge) at the bottom of the EDU would change very dramitically with only small changes in throttle pressure. At the time, I assumed that something was wrong with the gauge as I never fully trust the fuel economy meter anyway. However it appears the gauge is fine as my fuel economy really has plummeted.

Thanks chaps.
 

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Unfortunately cats can mask overfuelling problems because they are doing their job i.e. burning off incomplete combustion products, so passing the MOT is not necessarily a sign of good health!

I wouldn't discount the lambda sensor, and other likely culprits IMO are a faulty air intake temp sensor or coolant temp sensor. Either of these could make the ECU think that the engine is still cold and so supply more fuel than needed.

A dirty AIC valve wouldn't normally result in high MPG unless it was stuck open, in which case you would notice a high idle.

I think it would be worth getting it checked out with Tech 2- it can tell you the temps the sensors are reading. If they look OK then it's probably the lambda sensor.

As a last distant possibility, it might be worth trying some injector cleaner. A partially stuck injector could be throwing extra fuel in.
 

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Discussion Starter · #7 ·
k9 Saab: I am going with a full tank. Just for 2 or 3 runs up the strip!

Bubbles: Thanks mate for the info. Good point, I had forgotten that the cat may mask high emissions ie HCs from not completely burnt fuel.

Your other suggestions, would these not cause activation of the CEL?
Sorry, whats a Tech 2? I am assuming its a diagnostic computer. Is this from a main saab dealer only or would my indie be likely to have one?

My last two tank fulls of petrol have included a large dose of injector cleaner. but thanks for the suggestion anyway. I didnt think this would be the problem but it was a cheap thing to try!

Something else that I did today was to reset the ECU (disconnected battery for about an hour) and then did an adaptation run. 2500 - 4500rpm in 4th.
This actually looks like it may have helped although I need to use the car a lot more before I would be confident to state any real changes.

Thanks all for the help.

On a fun note, do you think it would be worthwhile treating the car to a tank of optimax and octane boost? just for the santa pod run.
 

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Yup, Tech 2 is a diagnostic computer. A decent indy will have one.

Another possibility, although less likely, is a faulty throttle position indication, which might mean there's no fuel cutoff on overrun.

Optimax/ocatne booster will certianly give you more go- you just need to make sure you've fully adapted the car to get the best out of it.
 

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Discussion Starter · #10 ·
Had the car tested with the Tech 2 computer. They didnt find anything in particular wrong. He just reset and callibrated it....callibrated what I dont know as I forgot to ask. Doh!

Since I reset the ECU and did the adaptation run things have improved a bit anyway.

Also, something that I had forgotten about is while I was having the DI cassette problems I changed the air filter to a new standard one.
The old one had completely disintegrated. Could this potentially be why I was getting better fuel economy before, due to the very free flowing (ahem!) air filter? And since the new, actual, air filter is in place my fuel economy has got worse?

Cheers 9k
 

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Discussion Starter · #11 ·
Can anyone answer the air filter/ fuel economy query? I am tempted to get a high performance one if it helps a bit with fuel economy.

Any recommendations?

K&N, ITG, JR, or maybe an induction kit from Elkparts.

Anybody got anything good or bad to say about any of those or to recommend an alternative?

Cheers
9k
 

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Discussion Starter · #13 ·
Yep, I've used a couple of bottles of injector cleaner. Didn't seem to make much of a difference unfortunately.

I'm using the same cheap supermarket fuel as I was when I was getting fairly repectable fuel economy.
I wonder if I should give it a tank of Optimax?

The only thing I can think of was the massive difference in the state of the air filters, old to new.
Thanks for the suggestions.
 
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