Mysterious behaviour of a 4.2EFI

Grazv8 · Nov 24, 2016

Hi guys here's one that has me baffled (doesn't take much!)
So here's the problem, starts ok, feels powerful and smooth for about 20 minutes of driving then all of a sudden it's like someone has flicked a switch labeled 'bag of spanners'.
Symptoms are, noticeable loss of power, and what I can only describe as a clattering from bulkhead area when under load. Fitted new spark plugs, dizzy cap, rotor but same as before, 20 minutes of pure fun then, it's back to the bag of spanners again!?
Vehicle is a landrover 90 manual box with a 1994 4.2EFI
I pulled the plugs and they seemed quite sooted up in a short space of time if that's a clue.
Also if I decide to take her up to 60-70mph she gets there but it sure feels like she's working very hard to achieve it, the word 'cruise' does not spring to mind!!!!
Any thoughts please guys??

cooltide · Nov 24, 2016

Pinking?

Grazv8 · Nov 25, 2016

Hi thanks for reply! It certainly could be it has the characteristics of pinking but I've never experienced pinking on any vehicle before so wasn't sure, if it is, what causes it to start pinking after about 20 minutes of running well?
Sounds like a sharp tapping/clatter like I mentioned, I put higher octane fuel in to see if it helps but nothing really noticeable improved.
i've turned the dizzy anti clockwise a bit but no good (won't even start) I cannot turn dizzy clockwise any further because the vac advance hits the inlet coolant hose!!

cooltide · Nov 25, 2016

Grazv8 said:
Hi thanks for reply! It certainly could be it has the characteristics of pinking but I've never experienced pinking on any vehicle before so wasn't sure, if it is, what causes it to start pinking after about 20 minutes of running well?
Sounds like a sharp tapping/clatter like I mentioned, I put higher octane fuel in to see if it helps but nothing really noticeable improved.
i've turned the dizzy anti clockwise a bit but no good (won't even start) I cannot turn dizzy clockwise any further because the vac advance hits the inlet coolant hose!!

It would be clockwise to retard it, and pinking would occur when fully up to temp under full load / low revs.
If heads have been skimmed / compression ratio is higher you end up with a narrower window of spark timing on 95ron.
Since you have tried 98 with no improvement, could be something else but worth checking timing (and establishing tdc mark on crank pulley is correct)
A problem with operating temp can also make things worse but you don't mention any overheating problems. Are you running viscous fan of electric, are they working, and if electric, is the polarity / direction of travel correct.

Gazbo · Nov 25, 2016

Grazv8 said:
Hi thanks for reply! It certainly could be it has the characteristics of pinking but I've never experienced pinking on any vehicle before so wasn't sure, if it is, what causes it to start pinking after about 20 minutes of running well?
Sounds like a sharp tapping/clatter like I mentioned, I put higher octane fuel in to see if it helps but nothing really noticeable improved.
i've turned the dizzy anti clockwise a bit but no good (won't even start) I cannot turn dizzy clockwise any further because the vac advance hits the inlet coolant hose!!

Not familiar with the model, but just a couple of thoughts from experience with other vehicles. Is there a catalytic converter fitted to the exhaust system? these can internally collapse, there is a platinum coated ceramic matrix that when it breaks up can progressively block the exhaust sufficient to impair or even completely kill the engine performance, it can occur gradually or happen rather suddenly, check for possible blockage by getting under the vehicle when exhaust has cooled and bump the converter from beneath, any rattling, like rocks in a can, will indicate collapse of the matrix and possible blockage.
Secondly, how is the fuel filter? it could be getting progressive but not permanent blockage which could cause the mixture to lean off and cause the lack of oomph and the "bag of spanners" sound. Also you need to do an accurate test and setting of the ignition timing with a timing light to see if some mechanical movement is giving rise to a wandering spark.

Grazv8 · Nov 25, 2016

cooltide said:
It would be clockwise to retard it, and pinking would occur when fully up to temp under full load / low revs.
If heads have been skimmed / compression ratio is higher you end up with a narrower window of spark timing on 95ron.
Since you have tried 98 with no improvement, could be something else but worth checking timing (and establishing tdc mark on crank pulley is correct)
A problem with operating temp can also make things worse but you don't mention any overheating problems. Are you running viscous fan of electric, are they working, and if electric, is the polarity / direction of travel correct.

Hi no overheating problems warms up steady and temperature sits at normal. I checked the comp' all cylinders around 180 psi and I notice it has a composite head gasket fitted. No electric fan fitted yet just the viscous. My only very basic attempt at timing checking was removing plug 1 and turning crank so that cylinder was at top, I noticed that the tdc mark on pulley was not lined up with the marker on the engine, could this be the issue?

Grazv8 · Nov 25, 2016

Gazbo said:
Not familiar with the model, but just a couple of thoughts from experience with other vehicles. Is there a catalytic converter fitted to the exhaust system? these can internally collapse, there is a platinum coated ceramic matrix that when it breaks up can progressively block the exhaust sufficient to impair or even completely kill the engine performance, it can occur gradually or happen rather suddenly, check for possible blockage by getting under the vehicle when exhaust has cooled and bump the converter from beneath, any rattling, like rocks in a can, will indicate collapse of the matrix and possible blockage.
Secondly, how is the fuel filter? it could be getting progressive but not permanent blockage which could cause the mixture to lean off and cause the lack of oomph and the "bag of spanners" sound. Also you need to do an accurate test and setting of the ignition timing with a timing light to see if some mechanical movement is giving rise to a wandering spark.

Hi thanks for reply, there are no cats fitted, I have just changed pump and filter which made her more responsive but didn't improve the clatter/pinking noise. I think you are right regarding having the timing checked, I will try to get it down to the garage this week and see what that brings. Is there anything else that could cause 'lean off' when full operating temp is reached?

Gazbo · Nov 25, 2016

Grazv8 said:
Hi thanks for reply, there are no cats fitted, I have just changed pump and filter which made her more responsive but didn't improve the clatter/pinking noise. I think you are right regarding having the timing checked, I will try to get it down to the garage this week and see what that brings. Is there anything else that could cause 'lean off' when full operating temp is reached?

Not really up on fuel injection, more an old school carby man, but still, sus out the exhaust system for some transient blockage, just to rule that out.
I do understand that temperature senders communicate with f.i. management but how the interface really works I am not sure . If what is happening has ocurred all of a sudden then you can almost bet that a mechanical or electrical component has failed
From what you are describing it seems like some form of mechanical disturbance to timing, maybe ignition, maybe valves, not even sure what engine it is but one thing for sure, I'd be real interested to know your eventual findings, when you reach the end of this, good luck in tracing what it is.

Gazbo · Nov 25, 2016

Grazv8 said:
Hi thanks for reply, there are no cats fitted, I have just changed pump and filter which made her more responsive but didn't improve the clatter/pinking noise. I think you are right regarding having the timing checked, I will try to get it down to the garage this week and see what that brings. Is there anything else that could cause 'lean off' when full operating temp is reached?

Not really up on fuel injection, more an old school carby man, but still, sus out the exhaust system for some transient blockage, just to rule that out.
I do understand that temperature senders communicate with f.i. management but how the interface really works I am not sure . If what is happening has ocurred all of a sudden then you can almost bet that a mechanical or electrical component has failed
From what you are describing it seems like some form of mechanical disturbance to timing, maybe ignition, maybe valves, not even sure what engine it is but one thing for sure, I'd be real interested to know your eventual findings, when you reach the end of this, good luck in tracing what it is.

cooltide · Nov 25, 2016

Grazv8 said:
Hi no overheating problems warms up steady and temperature sits at normal. I checked the comp' all cylinders around 180 psi and I notice it has a composite head gasket fitted. No electric fan fitted yet just the viscous. My only very basic attempt at timing checking was removing plug 1 and turning crank so that cylinder was at top, I noticed that the tdc mark on pulley was not lined up with the marker on the engine, could this be the issue?

It could be. Mark tdc on the pulley with tippex and ask your fitter to time it at 5 deg btdc (vac advance removed). He may have to remove the dizzy and refit to achieve. If you have 14 bolt heads (with the external 4 bolts) and the thicker composite gasket you may get more advance, but its a safe starting point which you can mark up on the dizzy / timing cover

Grazv8 · Nov 25, 2016

cooltide said:
It could be. Mark tdc on the pulley with tippex and ask your fitter to time it at 5 deg btdc (vac advance removed). He may have to remove the dizzy and refit to achieve. If you have 14 bolt heads (with the external 4 bolts) and the thicker composite gasket you may get more advance, but its a safe starting point which you can mark up on the dizzy / timing cover

That's great advice, I will do it tomorrow, and then get her down to the doctor early next week, will let you know what happens. Cheers!!

Grazv8 · Nov 25, 2016

T

Gazbo said:
Not really up on fuel injection, more an old school carby man, but still, sus out the exhaust system for some transient blockage, just to rule that out.
I do understand that temperature senders communicate with f.i. management but how the interface really works I am not sure . If what is happening has ocurred all of a sudden then you can almost bet that a mechanical or electrical component has failed
From what you are describing it seems like some form of mechanical disturbance to timing, maybe ignition, maybe valves, not even sure what engine it is but one thing for sure, I'd be real interested to know your eventual findings, when you reach the end of this, good luck in tracing what it is.

pete1987RRC · Nov 25, 2016

are you running petrol or gas, think petrol is 4-8 BTDC gas on mine is on the o of before.
Hard to imagine what could rattle from a Mecanical perspective which would cause such a power drop.
Is it still EFI?

I wonder if one of the ram tubes in the plenum came loose?

Grazv8 · Nov 25, 2016

HI, checked exhaust out this afternoon all seems ok, looking a bit thin in places though.( a bit like my hair! ) exhaust easier to replace though!
I will let you know when I find the problem, thanks a lot for your input you have got me thinking. cheers!

Grazv8 · Nov 25, 2016

pete1987RRC said:
are you running petrol or gas, think petrol is 4-8 BTDC gas on mine is on the o of before.
Hard to imagine what could rattle from a Mecanical perspective which would cause such a power drop.
Is it still EFI?

I wonder if one of the ram tubes in the plenum came loose?

Hi thanks for your reply, we think the clatter/tapping noise which is only present when under load, coupled with a noticeable loss of power is actually pinking/detonation, but why it does it when it does is a mystery at the moment. The engine is only on petrol and is still EFI.

pete1987RRC · Nov 25, 2016

Only under load must be pinking.
Is the dizzy vac advance pipe perished or leaking.
Have you changed the rotor arm, the bob weights below the plate in the dizzy are very easy to dislocate and jam.

Grazv8 · Nov 25, 2016

H

Gazbo said:
Not really up on fuel injection, more an old school carby man, but still, sus out the exhaust system for some transient blockage, just to rule that out.
I do understand that temperature senders communicate with f.i. management but how the interface really works I am not sure . If what is happening has ocurred all of a sudden then you can almost bet that a mechanical or electrical component has failed
From what you are describing it seems like some form of mechanical disturbance to timing, maybe ignition, maybe valves, not even sure what engine it is but one thing for sure, I'd be real interested to know your eventual findings, when you reach the end of this, good luck in tracing what it is.

HI I checked the exhaust out this afternoon, all seems ok, it's looking a it thin in places though (a bit like my hair!!) exhaust easier to replace though!

I will let you know what happens, thanks for your input you have got me thinking. Cheers

Grazv8 · Nov 25, 2016

pete1987RRC said:
Only under load must be pinking.
Is the dizzy vac advance pipe perished or leaking.
Have you changed the rotor arm, the bob weights below the plate in the dizzy are very easy to dislocate and jam.

I am totally new to rover v8's, one of the very first mistakes I made was pull the rotor arm off without holding down the shaft, and all the timing weight springs fell off!! I put it all together again and got it checked out all was fine, that was last year, I must admit I did wonder if i had unsettled something so double checked all is good. I put a new vac advance unit on at the same time. I have just checked the pipe by sucking on one end, I could see the vac unit working ok rotor arm turns and springs back ok so I feel quite confident all the internal gubbings are ok.( famous last words)

ukadamwest · Nov 25, 2016

Had a quick read through, do you get poor starting behaviour when it happens ?

the engine should reach operating temperature much quicker than 20 mins.. the distributor amp modules do suffer from heat exposure and will fail especially when hot, resulting in a weak signal, however the symptoms are more usually stalling and poor starting when hot.

oakey · Nov 25, 2016

Could pinking be caused by carbon build up in cylinders getting hot and predetonating mixture? What is mileage? If engine been running rich then carbon build up could be significant.
If its ignition timing then it should only pink under load and when load is removed pinking should disappear as the ignition catches up with engine revs.
If I understand you correctly, the pinking starts then doesn't get better or worse dependent on load?

Mysterious behaviour of a 4.2EFI

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