348 Missfire Problem

Hi Guys, Hope someone can help.

I have a low rev missfire with my 1990 384 Euro spec 2.5motronic. At idle its running on about 3 cylinders and when pulling away I have to dip the clutch a second time to stop it stalling. At high rpm it's fine.

So far I've,
Changed the plugs and leads.
Throttle switch tested and working
Replaced the MAF's and they read 383 and 387 ohms.
New Lambda sensors fitted.
Reset the ecu's

After resetting the ecu's I've run the engine for 10minutes without touching anything, but its running on 3-4 cylinders so it can't be learning the correct parameters.
The car is running rich on fuel so I'm wondering if ;

Fuel injectors are leaking?
Temp sensor on the engine not working and hence over fuels because it thinks the engines cold?
Cat temp ecu's playing up? No cats fitted and the thermocoples tied out the way.

Any other ideas??

I've ordered a test button today so I can read the fault codes because euro cars don't have the switch as standard. Could someone let me know what pins it should be connected into?

Thank in advance guys.

 

or could it be the crank position sensors??

 

Check for air/vac leaks on the intake.

 

Thanks, Already checked and are ok.

 

only at Idle?

Air idle controls??

fuel pressure regulators- check the vacuum lines see if raw fuel is being pulled in to the intake.

does it idle right when it's started from cold?

 

I think you will find that the 2.5 Motronic does not have the capability to store and download fault codes - that came with the 2.7 Motronic system.

I would definitey take a look at the crank position sensors and the wires running to them. There are numerous cases cited here of misfires directly caused by loose or dirty connections at the crank sensors, or broken wires under the boots.

Good luck, please keep us posted on your findings!

 

+1

Took the words right out of my mouth.

I just replaced the entire wiring loom, for both sides, this summer do to exactly this. The shielding on the wires, under the rubber boots going to the CPS clip on the loom, have a tendency to get brittle and crack. Plus the wires will sometimes get broke off the back of the pins on the back of the female clip. You will also want to have a look at the condition of the shield going around the wire coming off of the sensor itself. I had one that was just about pealed all the way off.

 

I am with you boys on this one.

 

thanks guys thats a great help.

I hope to rule out corrosion in the connectors because I did an engine out rebuild and cleaned all the contacts with cleaner with great detail because this is normally a cause of many problems.

Didn't think of the fuel pressure vacuum pipe, that must be an easy one to check. More I think about it, I do get the RH bank running richer judging by the constant white smoke comming out the RH exhaust pipe. This may also be a reason why I struggle to restart the engine when hot.

Crank position sensors did come to mind. Candellera had that problem on his 348 but was more severe than my missfire, his wiring connector broke completely. Are the 2.7 crank sensors the same as 2.5? I may swap mine with a friends to check.

If the test switch on the 2.5 doesn't work, how do the dealers read fault code or dianose faults?

I'll let you know how I get on, may be a week or so because I'm moving house over the weekend. Plus point is I'll have a new garage to work in.

Again, Many thanks.

 

I'm not 100% on this, but I would imagine that the CPS are the same as for the 2.7? What say you Daniel-son?

So try swapping them with your buddy, and let us know either way how it works out.

 

Too rich = black smoke
Burning oil=grey/blue smoke (can be misjudged as white)
Burning coolant/water=white smoke


The 2.5 Motronic tracks error codes, but I don't know where you'd find a plug in to the wiring harness to get those codes on the 2.5. You'd also have to add bulbs behind the CEL dash plates (you can use your seat belt warning bulbs).


I'd check your oil fill reservoir for milky grey soup, and I'd check your coolant reservoir for a rainbow film on top.

I'd pull the lid off of your airbox to see if your airfilter is covered in oil, too.

Those are the easy tests. Then I'd yank off the little black vacuum hoses that go to each Fuel Pressure Regulator. Rub your finger on both ends of each hose, then smell your finger for fuel.

A fuel smell on your finger means that you have a failed FPR, which is an easy, cheap, and quick fix.

Put a timing light on each spark plug wire to verify spark, too. Hyper easy to do on the exposed wires on our 348's.

 

It's white smoke, quite normal for cars in England to have white smoke on startup as it's quite wet and damp here this time of year.

Will add some lights and try, Nothing to loose.

Air box and oil tank are fine.

Not tried this, will give it a go.

Not used a timing light but have tested each lead and I get a good spark.

Crank position sensors are the same 2.5 vs 2.7 so I'll have to be nice to a mate and borrow his for a quick check. Does anyone know the Bosch part number, I could then get some from a local store.

Again, Many thanks for all your help. I'll let you know how I get on.

 

That wouldn't have anything to do with crank position sensors, if that saves you any steps. If you were rich you'd have black smoke.

 

BOSCH # 0261210029

 

AFAIK M2.5 stores no codes and provides no diagnostics at all. You need to rely on pure detective work on these. I'm still working through the code in the EPROM, but so far, nothing to indicate that it does any diags.

White smoke of any sort is bad. Steam on the other hand is fine if the engine is cold, but once it's warm, it should no longer blow steam, unless the weather is really, really cold. If the weather is OK and the engine blows steam when warm, check your coolant level - it may be going down....

YMMV etc etc

 

I think your right, no means of getting a fault code reader to work so it's old detective work.

I think it's steam comming out the exhaust upon inspection. It stops when it's warm and the coolant is fine.

Many thank for the CPS part number, I may just replace them because they are only a few quid and even if it's not the cause, it will preventy me getting any cps faults for a few years.

I'm so keen to get working on the car but I'm moving house over the next few days which has to take priority. But I'll be in my new heated garage everynight nest week getting it fixed.

Really can't thank you guys enough for your help so far. I'll let you know how I get on

 

Glad to help out. That's what the 348 Brotherhood is all about. We look out for one another. We even look out for the 355 and Mondial T guys, right David. Hehehehe

 

Maybe another thing to check is the grounds attached to the driver left side intake valve cover (driver side in US, pass side in England). There were two or three wires toward the upper, rear of the cover that were loose on my car that would cause a bank of cylinders to die. The wires may be the grounds for one motronic. Also connect a fuel pressure gauge to see what is happening. Good luck!

Jeff Pintler
89 348tb, 86tr

 

LittleBlackFlash has still not resolved the issue. I've heard the car and the best way i can describe the mis-fire is overfueling on idle.

Imagine you had an old carb equipped motor with a manual choke and the choke was constantly on......vehicle idles erratically and then slowly clears as the revs increase. What sensor controls the fuelling on a 2.5 Motronic when the engine is cold?

 

At idle when cold for fuel/air (not spark!):
MAFs
water temp sensors
battery/alternator voltage
Throttle position sensor
Throttle cable/pedal
Throttle bodies
Air Filter (could be clogged)
Idle Air Control Valves
Idle Air Bypasses
A/C sensor
plenum vacuum
Fuel Pressure Regulators (could be faulty)
Fuel injectors (could be leaking/stuck/semi-clogged)
Motronic ECUs and onboard fuel/air mapping


When hot, add in O2 sensors to the list.

 

MAFs..............................................MAFs are fine, 383 and 387ohms
water temp sensors...........................Could be a suspect. Which of the 3 is temp sensors is it? Is it the same as the gauge?
battery/alternator voltage..................14v when running, should be ok
Throttle position sensor......................Continuityt between pins 1&2 on idle, 2&3 over 72% open.
Throttle cable/pedal..........................Allows the throttle to close, what else should I check?
Throttle bodies.................................Advice on setting these up would be useful.
Air Filter (could be clogged)................New filter, checked for any oil but it's fine
Idle Air Control Valves........................Could be a suspect. How do I check them? Candellara's car ICV make a noise for first 5 mins. Mine don't.... should they?
Idle Air Bypasses...............................Is this not the same as above?
A/C sensor.......................................Whats this?? and how do I check it?
plenum vacuum.................................No air leaks but not checked the vacuum. What should it be?
Fuel Pressure Regulators (could be faulty)...........................Not checked the air pipe yet (moving house)
Fuel injectors (could be leaking/stuck/semi-clogged).............Can get them reconditioned for £100, should this be a priority?
Motronic ECUs and onboard fuel/air mapping........................Can't change it so assume its ok.


When hot, add in O2 sensors to the list. Sensors changed and makes a difference, car dosen't seam to be so rich.

Still have to check the cranks sensors. Should I get a reading accross the 2pins when the crank the engine over by hand.. on off on off etc?
Do the crank sensors feed directly back to the ecu and which case can I check the reading there.

Sorry for so many questions...

 

3 temp sensors marked. What does each one do?
Image Unavailable, Please Login

 

Yes the cranks sensors go back to the ecu's via the wiring harness.

The other thing you will want to have a look at is the cam position sensor on the back of the intake cam on the 1/4 bank. Looking in form the back it's to the bottom right of the air box, the top cam. Check to make sure it's clean and connected properly. You may even want to pop it off to make sure the rear cam seal hasn't gone bad and allowed oil to get inside the sensor housing.

 

Yup, you want to chem 'em, but the crank sensors and cam position sensor are for spark instead of for fuel.

 

Nope. One sensor is for the gauge alone.

Is his 348 running properly when cold?

Nope. Different. The idle air bypasses are metal tubes that go around past (i.e. bypasses) the butterfly of each tb. Loosen the outer lock screw, then loosen the idle air adjustment nut to add air when the throttle butterfly is closed (e.g. at idle), then tighten down the lock nut while holding still the idle adj nut.

Especially useful if the electric idle air control valves are buggered, or if the idle air bypass tubes have grown a bit clogged with gunk over the years.

It's just a wire going from the A/C compressor to one engine ECU.

It should be balanced between left and right banks.

FPRs should be a priority test whenever you are running too rich or having trouble starting.

Not the top-most priority, but an eventual maintenance item.