My 3rd e24 ! few issues speedometer, loss of power under acceleration

[pepsih]

Hi Guys I just bought my 3rd 635csi!
the car is amazing, i will post some pictures as soon as the weather gets better, it has 42k miles on it, 42 thousand miles only! however the car has been sitting for a while but i was brought to life by a shop before purchase.

They have replaced the following: battery, coolant hose, radiator,
drained fuel tank, flush out lines install new fuel filter.
however it does have 2 issues:

1)
The cluster does not work properly basically tachometer, coolant temp, fuel consumption display and Service indicator light DOES NOT work,
speedometer and fuel tank level is working.

I removed the cluster and installed the one from my 2nd e24 and the tachometer is working, the S.I. light came on at start im not sure about the temp gauge because i didn't let it run for long, however i feel it is also working since it moved when i started the car.

I installed the cluster from my 3rd car to my 2nd car and it DOES NOT WORK.

I checked the voltage on the CR14250 BATTERies and it is 1.4V, however the old one is 1.8v(the one that the cluster has zero issues) i didn't have a chance to inspect properly the cluster board because i did not take it apart completely.
I'm currently checking the diagrams for any clues, but i have a feeling that the batteries are the issue
could you guys guide me?


2) the car is starting, idling perfectly, when i press the throttle to 3-4k rpm it works great however once i start to drive it
the car is losing power and it is stuttering, and then looks like it's trying to pickup power then stuttering...
since the car has been sitting for a while, and even if the shop cleaned the tank and replaced the filter, should i suspect some more contamination in the fuel system?
or it could be something else, bad plugs? as far as i know they were not replaced.

thank you for you help

Once the car will be up and runnnig and the weather wil be nicer i promise to do a proper photoshoot

Whats-App-Image-2021-02-27-at-8-26-40-AM.jpg

[wogden700]

#2 sounds like a vacuum leak.

[pepsih]

#2 sounds like a vacuum leak.

I'm not saying that this is not the issue but don't you think that the car would struggle at idle or when i press the throttle?
however in this case the car works perfectly fine it just start to acting up while im driving, during acceleration or even when im driving on higher (aroung 1500rpm) or above

[wogden700]

I do yes. I had a vacuum leak that presented similarly. I had a slightly low idle and the car would run fine under hard acceleration but any sort of normal acceleration or driving, it would sputter and buck and feel like it was about to stall but never did. I had a very bad vacuum leak from a rubber hose that it turned brittle and cracked.
A shop just worked on your car so it's possible they artificially increased the idle which could hide a vacuum leak at times
A simple check would be to open the hood with the car idling and then pull out the dipstick you should see a noticeable drop in RPMs as this creates a vacuum leak. if you don't get a noticeable drop in RPMs then you already have a vacuum leak. This method is not foolproof but is a great place to start..

[pepsih]

Thanks for the quick tip ill do the dip stick method once I get back home. However yesterday i removed the oil fill cap and the car noticeably drop in RPM.

[carsnplanes]

It sounds more fuel related actually. The demand for fuel is not very much at idle or free revving so it's hard to make a case with that. Under load, fuel needs are more critical.
Is your car an Auto or manual?
Were both fuel pumps checked for good operation
Fuel filter replaced? ( I see you said it was)
Fuel pressure checked at the rail?
FPR working and vacuum hose to it connected?
Opening the oil cap is a large vacuum loss so it would stumble anyway. Introduce a small leak like the pulling of the oil dipstick as others have said and see the response. If you see a drop in rpm then, then i think you're good with no other vacuum leaks.

A weak coil can cause stumble under load also. Check all grounds including body grounds at the left inner fender well ground gang point(brown wires). Remove, clean(wire brush both the terminals and the body side and reinstall)
Your bumpers look like 87 or older so I'm assuming a M30B34 engine.

[pepsih]

The car is a manual

https://ibb.co/GnKCh43

This is what the shop did before i purchase the car from the previous owner.

Mostlikely they only drained the tank and replaced the filter.

The car is VERY clean and it was always garaged inside so I think my research should be focused on the fuel, but ill definitely check the ground and coil.

[carsnplanes]

The car is a manual

https://ibb.co/GnKCh43

This is what the shop did before i purchase the car from the previous owner.

Mostlikely they only drained the tank and replaced the filter.

The car is VERY clean and it was always garaged inside so I think my research should be focused on the fuel, but ill definitely check the ground and coil.

So it doesn't sound like they solved for your stumbling under load. That tells me they didn't really do a test drive otherwise it would have appeared at that time if the problem was there all along.
Take advantage of being able to test for acceleration under load while sitting with park brake on and slowly try to move in 2nd gear. This puts a load on the engine without trying to actually move it if it were in 1st gear.(too much torque). The engine should be strong enough to try to move the car without actually feeling like it is stumbling in the process. If it doesn't take much to make it stumble this way, then sounds like fuel weakness or maybe there is still water somewhere. Water can act like a stumbling block but may eventually clear out.
Report back when you can.

[pepsih]

So it doesn't sound like they solved for your stumbling under load. That tells me they didn't really do a test drive otherwise it would have appeared at that time if the problem was there all along.
Take advantage of being able to test for acceleration under load while sitting with park brake on and slowly try to move in 2nd gear. This puts a load on the engine without trying to actually move it if it were in 1st gear.(too much torque). The engine should be strong enough to try to move the car without actually feeling like it is stumbling in the process. If it doesn't take much to make it stumble this way, then sounds like fuel weakness or maybe there is still water somewhere. Water can act like a stumbling block but may eventually clear out.
Report back when you can.

Hi,
im not sure 100% if I understood correctly but basically what you're asking me to do is the have the hand brake engaged? shift to 2nd gear and release slowly the clutch until the car almost cuts off correct?
if yes, i did that and it is not stumbling,
I actually had the opportunity to test drive it again yesterday, so I realize one more thing, if you accelerate gradually at higher gears (2 and up) the car run much better than if you press the throttle harder.
basically if you accelerate smoothly chances are that the car wont stumble( not always the case because at higher RPM IT IS stumbling) but if you're "rough" on the car and try to accelerate quickly the car will definitely stumble.

The reason why im trying to explain this is that i also suspect that the COIL is not giving enough juice to the plugs if I suddenly press the throttle, does that make sens, ?
Im not sure how old are the plugs i'll definitely change them soon but i doubt that all the plugs would be bad under hard acceleration, and i kinda know how the engine would react if it misfires.

Basically if i suddenly press the throttle the car start to JERK, and I look like I would be driving a stick shift car for the 1st time lol i does happen at any gear if i press the throttle hard enough

[DesktopDave]

Congrats on another E24! They're a hard habit to break, aren't they?

I'd be looking for about 3VDC on those cluster batteries, as I believe all later E24 got the lithium types. There's an updated board from Programa without a battery that's supposed to solve those issues permanently. It's expensive, and I've heard mixed reviews, but I've always been tempted to get one.

Cars that have been sitting for a while can have a variety of unusual problems. Low compression, sticky FPR, a dirty AFM, etc.. You have a massive advantage with all those known-good parts in your other E24s, swapping parts out is my favorite way to track down problems.

That part-throttle stuttering can be caused by a wide variety of problems. I'd start with the easy stuff - verify both fuel pumps are running. Pull the plugs and see if it's running rich or lean. Consider replacing them while they're out, do a nice valve adjustment while you're there. I'll also give the spark plug wires a wiggle when I'm testing them for resistance. There are updated Kingsborne plug wires that are well regarded. A new cap & rotor is likely a good idea.

Consider a smoke tester to track down vac leaks. Then get into the nitty-gritty stuff. Test all the sensors to BMW spec, especially the critically-important AFM, DME coolant temp, speed & position senders. Here's a good tutorial for chasing down Motronic problems:
https://www.hpsimotorsports.com/motronic-
He's updated it several times, some parts will not pertain to your car.

[carsnplanes]

Hi,
im not sure 100% if I understood correctly but basically what you're asking me to do is the have the hand brake engaged? shift to 2nd gear and release slowly the clutch until the car almost cuts off correct?
if yes, i did that and it is not stumbling,
I actually had the opportunity to test drive it again yesterday, so I realize one more thing, if you accelerate gradually at higher gears (2 and up) the car run much better than if you press the throttle harder.
basically if you accelerate smoothly chances are that the car wont stumble( not always the case because at higher RPM IT IS stumbling) but if you're "rough" on the car and try to accelerate quickly the car will definitely stumble.

The reason why im trying to explain this is that i also suspect that the COIL is not giving enough juice to the plugs if I suddenly press the throttle, does that make sens, ?
Im not sure how old are the plugs i'll definitely change them soon but i doubt that all the plugs would be bad under hard acceleration, and i kinda know how the engine would react if it misfires.

Basically if i suddenly press the throttle the car start to JERK, and I look like I would be driving a stick shift car for the 1st time lol i does happen at any gear if i press the throttle hard enough

Ok, I get it. So basically on large throttle openings or demand for fuel, it stumbles. If you haven't pulled the plugs to check the gaps, I would do that simple job first. Next, it sounds like possibly the Fuel Pressure Regulator(FPR)may not be holding pressure in the fuel rail.
From the Bentley Manual, here is the FPR explanation and tests.

Description of operation: fuel pressure regulator
Depending on requirements, the fuel pressure regulator regulates a low or high fuel pressure. This requirement is set
with the help of the pressure regulator.
Depending on the engine's operating state, less or more fuel is needed:
-
at idle speed, less fuel
-
at full load, considerably more fuel.
The injection rate is precision-adjusted by means of the injection time; the injection time is controlled by the DME.
The partial vacuum in the intake manifold serves as engine load information for pressure regulation. The diaphragm of
the pressure regulator is actuated with this partial vacuum.
A partial vacuum builds up in the intake manifold during idling operation or in overrun mode. Depending on the partial
vacuum value, the fuel pressure decreases starting out from the nominal value. The nominal value is stamped in the
fuel pressure regulator housing.
At full load, the partial vacuum in the intake manifold is approximately equal to zero. The fuel pressure regulator
regulates the fuel pressure to the nominal value stamped in the housing.
Description of operation: fuel pump
The control function of the fuel pressure regulator must be ensured in all operating states. The fuel pump must
therefore always be able to generate a higher fuel pressure than the pressure regulated by the pressure regulator.
Description of operation: fuel return line
When the engine is at a standstill and the ignition key is in position 0, the fuel return line after the pressure regulator is
at zero pressure.
Description of operation: pressure retaining function
The pressure regulator closes when the engine is at a standstill and the ignition key is in position 0. The fuel pressure
in the delivery line is retained over an extended period. A non-return valve closes in the fuel pump. These measures
help to retain the fuel pressure in the fuel system. Extended starting times are thus avoided.
Complaint: drive characteristic faults, lack of power
-
Run engine at idle speed and measure fuel pressure.
-
In order to simulate "full load" state:
Disconnect vacuum hose from fuel pressure regulator and measure fuel pressure.
The measured value must increase by 0.4 to 0.7 bar depending on the engine. Note down measured value.

[1986series6]

Jody,

How are you? When you state: "A non-return valve closes in the fuel pump". Is that the lift pump in the tank?
Where would that valve be located for the #8 fuel pump?

thanks
Bob V

[carsnplanes]

Jody,

How are you? When you state: "A non-return valve closes in the fuel pump". Is that the lift pump in the tank?
Where would that valve be located for the #8 fuel pump?

thanks
Bob V

Bob,
Hows' it going with you?

The above description excerpt is from the online Bentley manual.
The non-retrun valve or "checkvalve" as it is sometimes called, is in most fuel system pressure output lines. Since our E24's have two pumps, I am not sure which of the two contains the non-retrn valve in it. I would suspect the main pump as that is the pump that is the first stop back from the engine's fuel rail. If working correctly, the non-return valve will keep a column of fuel between the pump and the fuel rail in order to keep a level of head pressure ready at the injector rail. Additionally, the FPR while no vacuum is applied, should lock off fuel as well, from returning to the tank. Both of these devices should keep enough pressure in the injector rail for a good next start. Over time of course, the pressure may bleed off. I believe the ignition switch in the on and crank position, the pump puts out and continues as long as the reference sensor detects spark and running. If not, the pump ceases to pump as controlled by the ECU.

[1986series6]

I'm asking because the new high flow pressure pump will cycle for 3 seconds when ign. turned on.
The car starts right up cold and will stall after a minute or so. If I cycle the pump twice before starting
the engine won't stall and warms up ok.

Also, if I cycle once, sometimes after a little hard acceleration it will starve for fuel and stall.
It won't restart until I cycle the pump twice. Then very hard redline shifting is ok. I have apex in Clifton
checking the in tank pump. So far the only remedy is an OEM BMW for over $400 or Walbro #255 $100 fabricated to fit. I know that Airflex had them
but no longer manufacture.

[carsnplanes]

I'm asking because the new high flow pressure pump will cycle for 3 seconds when ign. turned on.
The car starts right up cold and will stall after a minute or so. If I cycle the pump twice before starting
the engine won't stall and warms up ok.

Also, if I cycle once, sometimes after a little hard acceleration it will starve for fuel and stall.
It won't restart until I cycle the pump twice. Then very hard redline shifting is ok. I have apex in Clifton
checking the in tank pump. So far the only remedy is an OEM BMW for over $400 or Walbro #255 $100 fabricated to fit. I know that Airflex had them
but no longer manufacture.

Bob,
Not sure or remember what mods or changes you had done to the fuel delivery as far as the pumps are concerned. Also not sure what changes if any you had done to the cold start system circuit. If there's anything still stock on your engine as far as that is concerned, you should still have the thermo time valve on the coolant manifold which controls the cold start valve/7th injector, of course assuming you u still have the original ECU which controls that function and the CSV is still installed. As far as the pump management, yes, you should have a brief power on of both original pumps in the "run" and while cranking. Do you still have the original style FPR attached to the front of the fuel rail? That and the original pump check valve should keep enough pressure in the fuel line and injector rail for a while. It sounds like it is not if you have to prime the rail with three blasts of fuel pump with your ignition switch on-off-on.. Do you still have two pumps?

[Bert Poliakoff]

From the little bit I am starting to learn due to a possible conversion, Motronic 1.3 does not use a CSV. I think Bob has a stand alone system so I wouldn't even begin to start guessing how that functions

[DesktopDave]

I think you're on the right track, definitely. If pressure is lost in the fuel rail, you'll definitely get some hard starts and cold-running problems until the pressure builds across our (very long) fuel rail. I'd guess your 'two-prime' method is just a little better at fully pressurizing the FPR, lessening the pressure drop. The engine needs substantially more fuel when cold, especially at high RPM.

I'm pretty sure the Motronic 1.0 cars had the anti-backflow valve on the output side of the high pressure fuel pump. I have one in the shed, I'll take some pics if I get a chance. It's actually a removable threaded fitting on some Bosch pumps, but it can't be easily adapted to off-the-shelf pumps with barb-type fittings. A leaky FPR or injector (don't forget the cold-start injector) would de-pressurize the system pretty quickly. The FPR is quite hard to diagnose as any 'leaks' are simply returned to the fuel tank, and it's a completely mechanical system. I'd be tempted to leave a fuel pressure gauge "teed" into the input hose at the back of the fuel rail, run the car, let it sit, see how long the pressure lasts. There is a BMW spec about residual system pressures somewhere, maybe the Bentley? On a related note, I'd guess that the early systems were highly depended on fuel pressure, the older cars had several devices to keep pressure tightly regulated, including some passive inline pressure regulators. Later pumps eliminated many of these systems.

I didn't want to threadjack, but this is for Bert:
I can 100% confirm all that. Motronic 1.3 eliminated the stand-alone cold-start enrichment setup. That's a big plus on the 1.3 conversion, along with the integrated ICV idle controller system. Parts like injectors and sensors are also far more common, cheaper and easy to find. Upgraded versions are available in many makes and models. You'll also need a different temperature sender for the gauges. I believe it's part 13621709966, very widely used and cheap. This updated sensor doesn't integrate the secondary switch to support the coolant overheating dash light. Unused sensors in the coolant neck can be replaced with oil pan drain plugs, IIRC.

[Bert Poliakoff]

I am only thinking of converting if the 002 ECU won't run my lightly modified M90 motor. Lightly modified being a 284 cam and true 10:1 pistons and if it runs well then, I will insert a 2mm oversize throttle body into the mix and see what I get. I have had mixed feedback over the years about whether or not the 002 will run it with many saying it should be fine. I am also running total open loop. Waiting for the motor to come from the machine shop after it's second rebuild when I got only 20 minutes from the first before it literally trashed. Motor was rebuilt 10 years ago and waited until 6 months ago to be lit up so no way to go after original builder who was supposed to be one of the best in town. Oh, well

[1986series6]

Well, thanks for the input guys. So the in tank pump was not working, and the high flow outside pump was
doing all the work. I could get a direct BMW in tank assembly but I'm going to convert the in tank with a Walbro 255.
I'll fabricate to fit the assembly and I'm (almost) sure this will solve my problem.

Desktop Dave is correct, I had a cold start valve but with the stand alone ecu it enriches through the injectors.
My cold starts are flawless. Fires right up running @ around 1400 rpm and as it warms up slowly the rpms calm
down to 800 @ normal operating temperature.

Thanks again guys I'll try and do a picture-see-do but I'm not that great with writeups.

[pepsih]

Thank you for all your advices, ill keep you posted, for now i will focus on my instrument cluster issue, i don't feel like starting and driving the car without knowing it's temp.

[DesktopDave]

Thank you for all your advices, ill keep you posted, for now i will focus on my instrument cluster issue, i don't feel like starting and driving the car without knowing it's temp.

I was driving my car for a while without a working temp sensor. It was during the engine swap, it took me a while to figure out what was functional. Since I'm both cheap AND impatient, I took the car out regardless. I just took my cheap IR thermometer along for the ride, and drove around the neighborhood more or less within walking distance of home. I'd just pull over about every ten minutes to take the car's temperature. I was very happy with that IR thermometer's performance. You can check radiator effectiveness, fanstat function, block & head temperature, even which injectors are sticky (lean cylinders run far hotter at the exhaust pipes). All in all, an amazing tool.

I ended up using the thermostat housing as the baseline temperature. It was convenient, consistent, easy to get at. My favorite discovery of the day was that the entire cooling system wasn't really working at all. The engine-driven cooling fan clutch wasn't working. The fanstat switches were both functional, but the low-speed AND high-speed relays were defunct. Thank goodness the A/C could still turn on the aux fan. When the housing got up over 200 degrees F, I stopped off for a coffee break to let it cool off.

So the moral of the story, if you're interested, is that a cheap IR thermostat is FAR more accurate than the VDO gauge in an expensive BMW. Who knew?

Be aware, if you follow in my footsteps , that an IR thermostat is not foolproof. It will not take a good temperature off highly reflective surfaces. I found that out when trying to tune carbs by temp. The motorcycle had chrome exhaust pipes, it was almost completely futile.

[pepsih]

PROBLEM SOLVED!!!!

DESPITE the fact that the mecanic replaced the fuel filter and cleaned the tank, he must done a bad job... looks like i had a clogged in the line. i was at the red light and when i when i put it in the 1st gear the car almost stalled, then i press little more gas and the car start to run great!
so i immediately went to the gas station and now the car drives great!


when it comes to the cluster the main cluster board is bad, i will try to send it to someone to get it fixed.

[1986series6]

I wound up getting the Walbro 255 pump and adapted to the assembly.
Hard time finding the correct size of the output hose (11.5 x 18.5mm).

Got it from https://www.belmetric.com/smooth-hig...gssptocsul1h91

Had to shorten the return tube I brazed on and remove the clamps holding the pump to clear the opening.
Used twisted wire to hold the pump to the return tube. I don't have photo of final configuration.
I shortened the overall height from 9.0625 to 8.9375.

Also, I used 6 x 12 hose as a spacer to fit on pump outlet and slide the 11.5 over the 6 for a tight connection.

This solved my starving fuel problem. Next is to swap out the line from the in tank to high pressure, high flow exterior pump.
It's 35 years old--enough said!

IMG_2084.jpg

IMG_2083.jpg