Two things that may or may not be related -

1. when starting the engine from cold - idle is very unstable for the 60 seconds or so. After that the idle is fine and the engine is solid. I am idleing about 1100 rpm when warm though.

2. On the road and under acceleration load I have a hesitation. As an example; when I'm on the highway and I'm doing about 70mph and I hit the gas, the hesitation is noticable and continues on/off for as long as I accelerate.

I really don't think this is an ignition problem because it would be more constant. I believe this to be a fuel delivery issue. Could this be something to do with the accumulator? I put on a new fuel filter last week in hopes that that might help the issue but there was no change. I was also thinking it might be an injector issue - perhaps a partially clogged injector/s.

Rob

Check the oil breather line for any vacuum leaks around the T Connector. Check all rubber hoses for plyability (They should be springy and supple under your fingers, but not want to give.) And as well, make sure your TB and WUR are functioning correctly.

I would check your Cold Start injector for signs of failure though.

Hi,

Thanks for the information. What is the TB and what are some basic tests that I can run to ensure both the TB and WUR are functioning properly.

I will check for vacuum leaks. To be clear; is the oil breather line the line that comes from the valve cover?

Also, the cold start valve - I'm assume you think this might be the issue with the cold start-up and not with the hesitation on the highway?

Many thanks,
Rob

It sure sounds like a vacuum leak. Make sure all of the hoses are snug, and that there are no splits. From the T by the valve cover, the small hose tends to split...
Tighten all hose clamps you have, particularly around the throttle body.
How much gas do you have in the tanks? Try putting a bottle of injector and fuel line cleaner in the tank and filling up with gas (premium of course!), if tightening doesn't do it...
Hope this helps!
Tim

Is the 1" ish tubing that goes from the a/r valve part of the vacuum system?

Also, the T-connecter and the hoses attached are in good shape. The small hose going from the middle of the T - is there a way to inspect that under the throttle body? I can't seem to get in there.

Is there a diagram of all the vacuum hoses that I should be looking at on my engine?

Thanks,
Rob

Bump

Make sure the in-tank pump runs, make sure the screen is clean, make sure the tanks are clean, replace the fuel filter, blow out the lines, replace all the vacuum hoses.

Hi,

I have already done the filter. Can I get at the in-tank pump and screen from the inspection hole under the back seat?

Also, I searched but could not find a diagram outlining all vacuum hoses on the engine. Does anyone have such a thing?

Is the rubber tube on the A/R valve considered vacuum?

Thanks,
Rob

1) Yes
2) I don't know of any diagram but the system is so simple you don't really need it
3) I don't know of anything called an A/R valve but I'm going to guess you are talking about the aux air valve, and yes a leak there is a problem. The hose down below the valve is the most common offender since it is hard to see and hard to replace and it cracks often

Hi,

You're correct - the Aux valve. The hose on the up side did have a crack in it and for now I have tape it up. My cold start idle is MUCH better and my warm idle has now settled down to about 900 RPM - in short; progress.

Now to figure out why I still have the slight hesitation under load. I will be inspecting the in-tank pump and screen tomorrow. Would the engine even run if the in-tank pump wasn't working? Also, what is the safest way to test this pump?

Thanks,
Rob

id replace ignition leads and distribitor cap if not done recently as it may be a weak spark. they are quite well supressed for radio interfearance as standard so any deteriation soon causes a weak spark. iv replaced mine with copper core leads and mine has stopped hesertating under load.

id replace ignition leads and distribitor cap if not done recently as it may be a weak spark. they are quite well supressed for radio interfearance as standard so any deteriation soon causes a weak spark. iv replaced mine with copper core leads and mine has stopped hesertating under load.

Hi,

The dizzy and rotor are new but the plugs and wires are from PO. I inspected the Bosch Platimums and although initially they were in very rough shape, I was able to clean them up and they look great. The plug wires "visually" look good (but what does that really mean).

What is the best way to test a plug wire?

I don't have a problem changing any of these items to fix this problem, I just don't want to chuck money at parts that won't fix the issue.

Thanks,
Rob

standard ignition leads are carbon inpregnated thread. these when new give less radio interfearance and resonable conductance (low resistance) but they deteriate with use so that the resistance increases. Iv replaced mine with copper core as this gives good conductance and doesnt deteriorate very quickly. this gives a better spark and so better economy and power. ideal ignition resistance for optium spark is 5-6kohms. increasing spark plug gap to 50thousands can also be advantagious for a bigger spark, more than this has been found to not help. good spark means faster burning of fuel which means more power may not be alot but in theory it should.

Hi,

I'm on it. I'm going to check the resistance in my wires this afternoon. I will also be inspecting my internal tank pump and the assiciated screen.

Do you know how to test the internal pump?

Rob

yeah, how do you test the internal pump?

I changed my pluggs this afternoon. I put in NGK Platinums and I gapped them to 46 thou.

I noted that the threads on the old plugs were damp with oil. Is this an indication of a ring or valve seal issue?

The resistance on the the plug wires was at least 6 ohms on each wire. I went for a road test after the new plugs went in and I still have a slight hesitation under load. I will be checking the tank pump and screen tomorrow.

Feedback is very welcome.
Thanks,
Rob

There's been a lot of discussion that platinum's do not work well in our BMW's. I don't have any personal experience, you might want to do a search.

As for oil on the threads I would say it's more than likely a leaking valve cover gasket, although it could be a ring or valve stem seal problem as well.

As for oil on the threads I would say it's more than likely a leaking valve cover gasket, although it could be a ring or valve stem seal problem as well.

Hi,

I'm so sure about the leaky gasket but there could be an issue with valve stem seals. I'm going to look into the difficulty level in checking and possible changing if needed.

I'll do the search on the platinums. I'm off to take a look at my internal pump and screen.

just make sure the plug is of the right heat range. if its too cold it will build up deposits, if its too hot it will burn away and may cause pinking/knocking. either way power will suffer if not near correct temp range

Platinum plugs don't work well. The best to use are bosch WR9DS (silver electrode, hard to find) or WR9DC (copper, easy to find) and autolite AR52 (You can order these at NAPA, they are mostly reccomended for hotter coils, I don't have much info on using them with the regular coil).

IMPORTANT: For those that don't already know, the hayne's book is WRONG about the spark plug gap. Try .035 instead of the reccomended .024-.028 and it will run alot better.


To test the in-tank pump:
Go under the car and take off the hose that connects the in-tank pump to the external pump. Remove at least one wire from the main pump and tape it up so it can't short out on something. Hit the starter for a second and watch for fuel spewing from the hose you took off. Yes the engine will run if the small pump isn't running but it isn't good for the big pump.

Platinum plugs don't work well. The best to use are bosch WR9DS (silver electrode, hard to find) or WR9DC (copper, easy to find) and autolite AR52 (You can order these at NAPA, they are mostly reccomended for hotter coils, I don't have much info on using them with the regular coil).

IMPORTANT: For those that don't already know, the hayne's book is WRONG about the spark plug gap. Try .035 instead of the reccomended .024-.028 and it will run alot better.


To test the in-tank pump:
Go under the car and take off the hose that connects the in-tank pump to the external pump. Remove at least one wire from the main pump and tape it up so it can't short out on something. Hit the starter for a second and watch for fuel spewing from the hose you took off. Yes the engine will run if the small pump isn't running but it isn't good for the big pump.

Thanks for the information - this really helps. I wish I would have known about the platinum info before I spent $28 on the NGK Platinums yesterday - such is life. I gapped them at 45 and the engine is idleing very smooth and my p/u is better than it was before. NAPA's gap recomendation for these plugs was 24. :rolleyes

Before I do the in-tank test - where is the screen that I should be looking for?

the temperature reqired is to do with the tune of the engine. a high bhp per litre reqires cold plugs, a low bhp per litre reqires hot plugs. its to do with the amount of fuel being burnt. the way the ignition works is the coil increases in voltage until there is enouth current to spark at the plug with a specific ignition lead+plugs+plug gaps so if fires at specific voltage. so say a normal setup reqires 12,000 volts and the standard coil is rated at 15,000 volts and a perforence coil is rated at 20,000 volts. the spark will still be fired at 12,000 volts with both coils. the advantage a performence coil has is in higher tuned engines which are blown eg turbo have a high combustion chamber pressure as there is alot more gas in there. this gives high resistance across the spark plug and so a larger voltage is reqired to spark the same gap. id personally stick to copper core plugs i think this other ones eg platiumn are gimics to get boy races to part with there cash thinking it will make there car go faster. multiprong plugs for example have been shown to lower bhp due to sheilding of the spark, the advantage muliprong plugs have is they last longer but that isnt normally a problem with plugs.

screen is on the intank pump. pull it out and you'll see it.

the temperature reqired is to do with the tune of the engine. a high bhp per litre reqires cold plugs, a low bhp per litre reqires hot plugs. its to do with the amount of fuel being burnt. the way the ignition works is the coil increases in voltage until there is enouth current to spark at the plug with a specific ignition lead+plugs+plug gaps so if fires at specific voltage. so say a normal setup reqires 12,000 volts and the standard coil is rated at 15,000 volts and a perforence coil is rated at 20,000 volts. the spark will still be fired at 12,000 volts with both coils. the advantage a performence coil has is in higher tuned engines which are blown eg turbo have a high combustion chamber pressure as there is alot more gas in there. this gives high resistance across the spark plug and so a larger voltage is reqired to spark the same gap. id personally stick to copper core plugs i think this other ones eg platiumn are gimics to get boy races to part with there cash thinking it will make there car go faster. multiprong plugs for example have been shown to lower bhp due to sheilding of the spark, the advantage muliprong plugs have is they last longer but that isnt normally a problem with plugs.
useful info - thanks! now the only thing left is to figure out how to differentiate the word "their" from "there" and how to spell "require" ;)

Thanks for all the input on this thread - including the spelling lessons - arrogant but very funny.:D

Good information on sparkage. So, I took the pump out of the tank, it really was not that bad - I was scared but it wasn't that bad. I did in fact see the screen. It was in pretty good shape overall. There was a little gunga on the screen right below what I'm going to call the "tube something something" but other than that it was clean and the pump worked well.

I have checked the resistance in the plug wires all over 6, changed the plugs and gapped to 45 thou AND cleaned the screen on the internal pump. The engine is smoother than ever but I still have a slight intermittent hesitation at higher rpms under load - so what's next? Where should I be looking now?

Rob

I haven't been following this thread that closely, so forgive me if this has been covered, but have you checked the air filter? This can cause hesitation at higher RPM's if it needs to be replaced.

Thanks for all the input on this thread - including the spelling lessons - arrogant but very funny.:D

lol
yeah, sorry, i didn't mean to be arrogant... just pointing it out. :stickoutt
and i do appreciate the info that he actually gave - i learned a lot from it - he answered questions that i've been wondering about for some time, but never bothered to ask.

Hi,

Air filter is brand new. Since I found a vacuum leak the hesitation has been better as per a 1 hour highway trip yesterday. There is still a vacuum hose that I need to get at under the aux valve.

One thing is for sure - I'm making very positive go-forward steps with this car :lol