Thread: 3.9 Rangie running rough - sort of. Help, please

I think we'll need some more history on the vehicle and details of exactly how he can cause it to happen with more than one way of stopping it thats not overly helpful as to fault diagnosis but it does allow some preliminary eliminations.

with no more than whats there theres a good 8 or 9 things it can be but to name a few it could be leads, a dying connection, a dying coil or a problem with the MAF/Map.

im leaning towards a faulty alternator........?

Sounds like too much voltage drop when a load is placed on electrical system
Poss alternator or what about the earth strap for the injectors at the back of the heads loose/bad contact. Or bad earth to coil or just plain bad earths?
Really need to know if it does it on lpg as well as fuel

Brad

Gents

Some further info....

AFM is recently installed, and I'm sure it's OK.Tune voltage set at 1.5V, and CO emissions are well inside limits. Dyno run showed no leaning out at road engine speeds (even high engine speeds).

Battery - nice, new, shiny, SuperCharge jobby (well, 07/07..)

Alternator - substituted Bosch - similar Ford type mounting. Internally regulated, externally excited (!). Tach runs OK off phase tap. Current well held and voltage drop 0.3 volt with everything running, including lights and air.

With the suggestions so far, it's looking like some dodgy earth doo-daa thingy, so I'll get #1 to check all the engine bay earths - remove, clean with steel wool, replace and check again.

I'll also get him to replace the coil (EFI type) and check all the connections on it.

OK, thanks so far - what'll be his next task(s)?

TIA

Pete

Sigh,Its a well known and documented case that The Bosch alternators create more "hash" when under load than Lucas.
This most commonly affects the RPM signal from the coil to the ECU which causes rough running under electrical load around 2000-2500RPM

The fix is to re route the wiring from the Dizzy to the coil away from the alternator, or to subsitute properly earthed Coax for the wiring.
Regards Philip A

I had a 1992 VogueSE recently where there was too much voltage at the coil, when headlamps were switched on there was almost 15V at the coil, and misfiring was happening at those revs too. It had a Bosch replacement alternator with a red coloured higher output voltage reg fitted. I fitted a 13.8V reg assembly(Black coloured) and all was well again.

I was told about this by an auto elec, I hadn't realised there were different/ selectable regs for these bosch units.

I found the problem was solved by disconnecting the exciter wire, so alternator output was Nil. The problem disapeared. (Don't try this with a EAS model, it will induce a non self clearing fault code....)

PhillipA has a point though. I wonder if it had more to do with electrical noise rather than actual output?

JC

if you suspect alternator noise have him temporarily hook up a big capacitor like the doof doof guys use between the alternator and the battery (it'll come with the appropriate wirings/warnings) and see what that does for you.

PhillipA, thanks for the heads up re Bosch products! You refer to coax cables for the distributor wiring - low voltage, I assume. Do you suggest a shielded cable for both of the leads from the dizzy amp to the coil?

Justin, will removing the exciter cable from the alternator prevent its correct operation? Thanks for the check-out bit on the alternator. It has a black regulator, same as most Magna/Ford.

Dave, thanks for the capacitor hint. After the latest of his blown-up head unit transplants (kid with hair clips in CD slot), a big cap could be a help in other ways!

Still looking...


Pete