E38 735i low on power 15mph top speed

[stefan]

Well after buying my e23 and doing a partial restoration on it I have now got a 97 E38 735i with all the toys and only 85,000 on the clock.

I only paid £200 because it starts ok ticks over slow and eratic and will only do 15mph flat out

It was running fine then just lost power when the previous owner was driving it.

Any ideas what I should be looking for

[joem83]

Easiest thing would be to run a quick scan on it, bet there is elevtybillion sensors on it lol.

Does it rev ok in neutral? is it Auto or Manual?

[dickdasterdley]

Have a look on www.the7seriesregister.co.uk - there's some guru level 7 knowledge on there, a bloke called Timm is your man!

[stefan]

I have put it up on 2 7 series forums so will see what they bring.

forgot to say before last owner took the plenum of it had LPG and had the same problems on both fuels.

Even in neutral it was flat as you like when trying to rev, its Auto by the way, wonder if they did a 735 manual in the e38 that would be cool

[joem83]

Could the ht leads have deteriorated? Whip the plugs out and see if they are wet or burnt?

now I think about it, I don't think they did do any manual 7's

[automatic]

Sounds like the ECU has detected a fault and put the car into limp mode to protect the engine. My first move would be to put a fault code reader on it. Clear all the fault codes and see if it runs right then. If the fault comes back then you will need to change whichever sensor the code tells you is duff.

Most garages will charge £30 to link up but you can get a basic code reader yourself for about the same money from ebay. I have the full diagnostics software on my laptop but unfortunatly I am little far from you

[stefan]

No fault codes showing on it when the last owner had them looked at

[RobinJI]

Doesn't sound like any limp home mode I've ever seen/heard off, they'll usually restrict things somewhat, but they'd let you do more than 15mpg, as if you're restricted to that kind of speed you're a danger to other road users, and might as well just stop all together.

Did the previous owner take the plenum off before or after the fault appeared? A really bad vacuum leak could cause what you're describing.

[surprisingskoda]

Jun 15, 2011 12:18:54 GMT joem83 said:

Could the ht leads have deteriorated? Whip the plugs out and see if they are wet or burnt?

now I think about it, I don't think they did do any manual 7's

Very few, just in the 735 model, and maybe the 728. I don't think there was a 740 or 750 manual, and the 730 didn't last long enough to get the option. Probably was a manual in the dizzle as well.


What Robin says is right too - Limp Home Mode should allow about 45-50mph from memory.
If it isn't showing any fault codes it's kind of surprising - they have a sensor or three for everything. It's odd too that it wont rev in Neutral - when the gearbox is at fault, it can still rev in neutral/park but is limited in drive modes. So it's more likely not to be a gearbox issue (which is a relief I'm sure!). The most obvious/likely cause would be one of the CPS being faulty but that would show on a code-read.

[surprisingskoda]

Oh, also, disconnect the MAF/AFM then report back on revability

[bortaf]

fuel pump? no sensors on that or the fuel filter is blocked and dropping the pressure enough to only alow idle ?

[stefan]

I thought Fuel pump but performance is the same on LPG as well.

The owner removed the plenum after the fault, the plenum is unbolted but still in place as it is trapped by wiring, I will take it off as there is a pipe that goes from plenum to fuel pressure regulater that gets hot a falls apart so i will change that as the top end is mostly in bits.

[westy180]

Make sure the brake light switch isnt stuck on, this may cause the engine not to rev up as the ECU thinks your foots on the brake.

[gazjon]

I had a clio once that ran lovely till you hit 25 and it just went flat, turned out to be a blocked cat. Check the back pressure from the exhaut or remove oxygen sensor and see if it improves

[stefan]

Ok will check the brake light switch, some one else has mentioned the cat as well so will be checking both of them.

So much to check I think I like carb and Dizzy better I know more about them, thought my 1981 e23 728i was looking complex

[surprisingskoda]

It's not the brake light at all. My 740 has the light constantly on as the electronic handbrake is stuck on (and broken), but it will still top the ton 60 mph.

[stefan]

Well managed to put all the parts back togeather, does anyone do a manual would have made life alot easyer.

It does start but I am unable to see how it runs as it is jetting fuel out of the seals between the injector and the fuel rail on the front 2 injectors on the drivers side. The injector top seals must be goosed so will have to see if I can get these? (what a pain in the rear it took hours to work out were all the electrics went)

[stefan]

Ok well I have stopped it leaking fuel so have been able to run it up to temp and see what is happening myself.

It ticks over very lumpy and is no better under throttle, it sounds like it is running on 6 or 7 cylinders and shakes the car. It will not rev over 3 to 3 1/2 thousand revs and every now and again it miss fires which almost stops the engine and then it slowly builds up the revs again.

I have tried spraying WD40 around the engine when it is ticking over to see it the revs increase from the 500rpm it is ticking over at but nothing so I do not think it is an air leak so I think it must be ignition related which I suspected as it was running bad and petrol or LPG.

so?

coil packs
cam position senser
Air flow meter (Makes little to no diffrence when you un plug it, engine slows then picks back up to how it was before un plugging it)

any other ideas?

regards

stefan

[rodney]

do a compresion check , id put money on burnt valves , its common on lpg cars , normally around 150k miles tho , if scanner don't bring up codes then its mechanical most likely ,.

[stonyray]

my Laurel did this, it turned out to be the resistor pack for the injectors breaking down, she dropped on to 4 pots and would only hit 40. Check the injector plugs that they are cycling properly,