Persistant misfire at idle, stalls at idle in gear

[Swarvey]

The Vehicle: 1987 Range Rover Classic, 3.5 Injected V8

The Problem: Persistent misfire at idle, stalls if idling in gear, but fine throughout the rest of the rev range.

Steps I've taken (In no particular order):
* New rings all round - some were literally broken
* Valves have been lapped in
* Full VRS kit installed
* All brand-new tappets, original tappets worn correctly, so cam should be fine too
* Rockers and rocker arms unclogged, I could have been in a black & white minstrel show when I was done
* Injectors tested for leaks at far above standard fuel pressure
* New injector o-rings
* Tried a spare AFM (Lucas 2AM Flapper)
* Tried two spare ECU's
* Throttle pot tested fine (DMM)
* Rave ECU troubleshooting followed to the letter
* Leakdown tests
* Compression test post-valve lapping 125 PSI on each cylinder, it's low, but yay me! The previous figures were all uneven and as low as 90 PSI, comp ratio 8.13.1? Best i can make out on the stamping, not all characters are completely readable
* Ignition timing checked, and checked, and checked, oh and checked, and did I mention i've checked lol, could do it blindfolded by now, btw I'm starting from 6deg adv
* Distributor rebuilt
* Distributor pickup coil replaced - old one dead, completely, believe me and the Sunshine Motorway
* Distributor stator replaced
* Rebuilt distrutor into a donor housing, swapped base plates after cleaning and reconnecting bob weights, skipped the nylon locking ring for now, still works installed pickup coil, gapped to 0.203mm (smallest in my brass gauges)
* Tried spare coil
* New ignition leads all round
* Tried two brand new sets of stock spark plugs
* Now using Bosch four-earthed plugs (don't ask me why, i like 'em, they work great in the falcon, misfire was still there on two other sets of stock plugs)
* Fuses and Relays fine
* Gas analyzer on exhaust - tune the AFM & CO 1.5%
* Heads cleaned and reinstalled (with new gaskets, part of VRS kit)
* Valley Gasket replaced
* Leaking oil pressure switch replaced with new
* Replaced ECU harness
* Installed a spare tach (dash one won't work, taking tach signal from line attaching ECU to coil because my instrument clusters electronics don't match any wiring diagram i've found to date, including rave)
* Tried a Jaycar Digital Tachometer kit which seamed to kill all spark for some reason - yet to investigate that one
* Bosh ignition amplifier conversion (not me, but I just rewired it this morning)
* Alternator charging fine, keeps the battery topped up and believe me it's being well and truly abused at the moment with the constant starting and stopping
* Rebuilt starter motor after one of the brushes broke lose from it's mounting
* Yesterday I found running vac advance at manifold pressure, instead of throttle body pressure smoothed it all out as in totally gone, problem solved, tried more advance by timing light instead so I could put the vac lines on properly, didn't have same effect, I didn't have a T-Piece for the vac line, so I couldn't attach FPR, it drove and idled perfectly in gear, at stop lights without stalling, just had no power going uphill, i'm guessing because of the lack of FPR-Vac, doesn't matter, replaced all ignition wiring (pickup to amp, amp to coil, ign to coil) with new 3mm Twin-Sheath, soldered and heatshrunk crimps and gapped the pickup coil and stator today and things just got worse
* Brand new fuel pump
* Brand new fuel filter
* New fuel
* Higher octane fuel
* E10
* Regular unleaded
* Misfire seems to minimize when AFM removed, but still noticeable, still stalls at the most inopportune times
** More info **
* No O2 sensors on this model, no Onboard Diagnostics either
* No idle control valve on any of my three manifold sets nor is there provision in the wiring harness
* Non tune resistor on this model... i've got one, i plugged it in... wouldn't start... removed... kept for a trophy

I've basically gone through all this rigmorole to sort out bad fuel efficiency to begin with (was only getting 200km per full tank), but this misfire at idle has me completely stumped, I've been working on it for months!

Does anyone have any ideas? Something I've missed or overlooked? Underlooked? Something completely bizarre and out of this world like really giving VB that good college try instead of a real beer? *digs* Something completely obvious?

I love driving the Rangey, just hate having to either hold some throttle at traffic lights or risk stalling. Any help / ideas greatly appreciated.

[joel0407]

Persistent misfire at idle, stalls if idling in gear, but fine throughout the rest of the rev range.


Maybe put this in your subject line because currently it looks like your suffering general depression.

Starting it in the range rover thread might have helped as well.

I own a TD5 Disco. Sorry I cant help you with you vehicle but I'm happy to offer advise about how you should post a thread

Happy Days.

[Swarvey]

Righto then, mods please move or delete, apparently I can't write a forum post.

[Hoges]

Ummm ...this problem could apply to petrol engines in any many LR vehicles.. it's not model specific. I'd have thought that "tech chatter" is a good general place to get advice:angel:

I think you have partly solved it for yourself re. the inlet manifold vs throttle body as source of vacuum for the distributor advance. I don't know a lot about the early EFI Rover motors ...but all older engines I've had which have a dizzy + vac advance have used intake manifold pressure/vacuum to regulate distributor advance.

Decreased power under load (on hills) suggests lack of fuel and too much distributor advance ... was the engine "pinging" under load? Have you reconnected the fuel Pressure Regulator correctly?

[Ancient Mariner]

Sounds like a Vacuum leak Tec chatter fine by me;)

[Swarvey]

c
Ummm ...this problem could apply to petrol engines in any many LR vehicles.. it's not model specific. I'd have thought that "tech chatter" is a good general place to get advice:angel:

I think you have partly solved it for yourself re. the inlet manifold vs throttle body as source of vacuum for the distributor advance. I don't know a lot about the early EFI Rover motors ...but all older engines I've had which have a dizzy + vac advance have used intake manifold pressure/vacuum to regulate distributor advance.

Decreased power under load (on hills) suggests lack of fuel and too much distributor advance ... was the engine "pinging" under load? Have you reconnected the fuel Pressure Regulator correctly?

Thanks! Yeah I posted here because I thought a misfire was very much NOT restricted to Range Rovers.

I thought I'd solved it too, but after gapping the pickup coil today, problems got worse, barely got it to run at all be fore the sun fell out of the sky. I'll be having another look at it tomorrow. The loss of power I attributed to not having a vacuum line running to the fuel pressure regulator, it wasn't pinging, just had to put the boot in hard and force it to kick down. Yes I could adjust the kickdown, but I'd still like the vac hooked up by the book, I figure it's gotta be like that for a reason.

[Swarvey]

Sounds like a Vacuum leak Tec chatter fine by me;)

Just picked up a need vacuum gauge yesterday, havent had a chance to check for specific leaks yet, but manifold pressure is well inside the greens, stable too, maybe a something to test tomorrow.

[joel0407]

Righto then, mods please move or delete, apparently I can't write a forum post.


DELETED?

Don't get too excited.

It just helps those that can help you find the thread. some of us frequently check all "New Posts" and when your running down the list it helps to know what the thread is about. I find it a tad annoying when I open the thread and find it's nothing i can help with and since I dont have a Range Rover petrol, It's not of interest to me. It just makes browsing the forum less enjoyable.

I appreciate you changing the subject line. Thanks.:)

Happy Days.

[Scouse]

Try running the engine with the alternator belt disconnected.

I haven't heard of a dud alternator affecting an early injected Classic but was involved for days in chasing a mid rev range misfire in an early 3.9 Classic.

Turned out the alternator had a diode problem & was causing interference to the injection system.

For 5min of your time, it's worth a try.

[bee utey]

Having the fuel pressure vacuum hooked up or not won't change the full power as WOT has no vacuum anyway. All that happens is that it runs rich at light load, all other things being correct. If you have the dissy vacuum connected to full vacuum, as the idle revs drop the vacuum drops, timing retards and that increases the rate of stall.

Make sure your pickup-to-ignition module wires are well away from the alternator or electrical interference will play havoc with the spark.

Adjust the idle speed up by using a 3/16" allen key in the recess on top of the throttle body.

Flip the plastic cover off the MAF, then run the engine, and gently manipulate the wiper arm and see if it runs better at different positions than the one its at. You can change the spring position so that the wiper arm is where it runs better. Try different positions and test drive. I've done this a few times on these horrors, it makes all the difference.

Oh and the stock RR tacho runs off a tapping inside the alternator, white/grey wire. This wire won't run a regular tacho.

[Swarvey]

Thanks guys, 2 votes for alternator, I'll disconnect the v-belt tomorrow and see if it makes a difference.

Bee utey I was hoping you'd pop in, I was re-reading your thread regarding the Bosch ignition module conversion last night which is why I too a fair bit of time binding, soldering crimping and heat-shrinking all the brand new stuff this morning. I didn't do the original conversion on this rig, but now I know for sure it's right. My ecu reads engine speed through a black n white wire through a relay to the coil neg, This is the same wire I tapped into for a Rachel signal on a 2" pod tach, seems to disagree with my new dmm which reads rpm though an inductive pickup though. Could that be an issue?

As for the flapper I've studied it thoroughly both in text and in practice. Which is why I've borrowed my mates gas analyzer so I can tweak the afm and get the mixture just right

[PLR]

The Vehicle: 1987 Range Rover Classic, 3.5 Injected V8
* Yesterday I found running vac advance at manifold pressure, instead of throttle body pressure smoothed it all out as in totally gone, problem solved, tried more advance by timing light instead so I could put the vac lines on properly, didn't have same effect,

it drove and idled perfectly in gear, at stop lights without stalling,

replaced all ignition wiring (pickup to amp, amp to coil, ign to coil) with new 3mm Twin-Sheath, soldered and heatshrunk crimps and gapped the pickup coil and stator today and things just got worse
.


G`day ,

using manifold vacuum as you did moves the backing plate to its full travel which inturn changed the orientation of the wires within the distributor .

From what you`ve written it seems you have changed these wires but from your explaination it`s saying the fault is with these wires or related .

The fuel pressure regulator requires vacuum at low revs/idle to lower the pressure so the pipe not being connected should affect it at low revs/idle

[bee utey]

Not sure if I'd add anything to the white/black wire, there may be a resistor between the ECU and the coil. Take the tach wire straight to the coil (-). If your coil is producing random firing from interference your tach will read high.

Setting the mixture by adjusting the MAF is pointless unless your fuel pressure regulator is working correctly. Try a pressure gauge. Vac hose off means increased fuel pressure at idle so no good once under load. That is why I do a "dynamic" tune, i.e adjust the MAF and see how it drives. Don't need a fancy analyser to feel it go better.:)

[Swarvey]

@PLR - I found that it actually required very little suck to even out the rpm at idle, I was just doing the basic test (suck on pipe and see if it holds your tongue) to see if the vacuum advance was working.. I only tapped into the manifold vacuum because it was constant. Constant vac advance smoothed out the idle so I left it there n took it for a drive.

When I say I changed the wires, I didn't mean on the pickup coil itself, there's the old crimps from the OEM amplifier, so I made new cables to go from here (via small blade crimps) to the Bosch module, as per bee uteys guide. I'm guessing you're thinking something along the lines of broken wires on the pickup coil? Put the dmm on the crimps and managed approx 3.1k ohms, which is okay according to rave. Sucked on vac to see if resistance changed and it was stable.

@bee utey - yeah I'll remove the tach from there too, realistically I don't need it, and it doesn't agree with ( has at least once shown higher rpm than) my new dmm with inductive pickup.

I totally agree, I've tuned it "dynamically" many times, but when troubleshooting I like to see the numbers and compare them to factory spec too aid in diagnosing the engine. When I get serious about tuning I've got more hardware at my disposal, o2 sensors, afr gauges among other things. Saving for a DIY megasquirt too.

[Swarvey]

Okay here's what I ended up with, I went to rebuild the dizzy with different weights to sort out the advance curve. Pop the dizzy cap off to find the center button just casually falling out of the cap. What a ****er! That was a brand new cap only a few months ago! So I rebuilt the dizzy with a replacement stator (gapping the old one was a pain, I haven't measured it but I'm sure one of the teeth was longer than the rest), put it all back in with the original cap, set the static, started up first turn.set the timing, removed the vacuum line and it's purring like a kitten, even in gear! I'll leave the vacuum connected directly to the manifold for now, it can't hurt. With the rebuilt dizzy in I was able to reset the idle speed so timing was set to 6deg and we'll see how it goes on this afternoons school run.

Yup, definitely solved, not sure whether it was the weights or the stator, but it's definitely fixed. Very drivable, loads of power, even spun some wheels by over-eager use of the throttle.