Difference between revisions of "Petrol engines Diagnosing faults"
m |
|||
| Line 21: | Line 21: | ||
===Ignition causes=== | ===Ignition causes=== | ||
'''Aidan:''' Some may remember Project Caravelle had a problem once upon a time following fitting of new parts during service that he couldn't resolve and ended up throwing in the towel and selling the van at a big loss, then new owner replaced leads with a good old set and it was sorted for a tenner, just because new don't assume they are good, (lets face it nowadays what if anything is made better than it used to be) '''if anything is changed, especially if it's not because of a fault, keep the old to be able to revert if necessary.''' | '''Aidan:''' Some may remember Project Caravelle had a problem once upon a time following fitting of new parts during service that he couldn't resolve and ended up throwing in the towel and selling the van at a big loss, then new owner replaced leads with a good old set and it was sorted for a tenner, just because new don't assume they are good, (lets face it nowadays what if anything is made better than it used to be) '''if anything is changed, especially if it's not because of a fault, keep the old to be able to revert if necessary.''' | ||
HT leads, rotor arm, coil, ECU, | |||
===Carburretion causes=== | ===Carburretion causes=== | ||
Weak misfire/hesitation OR grossly overfuelling | Weak misfire/hesitation OR grossly overfuelling (temp sender/blocked air filter, stuck choke etc) | ||
Air leaks anywhere between carb and cylinder (flanges/manifolds, vacuum pipes etc) | Air leaks anywhere between carb and cylinder (flanges/manifolds, vacuum pipes etc) | ||
Fuel starvation (fuel filter, tank feed blockage, pump failing) | |||
===Injection/ECU/AFM/ISU causes=== | ===Injection/ECU/AFM/ISU causes=== | ||
| Line 33: | Line 36: | ||
[[Petrol engines intermittent 2.1|Temp sensor]] <br> | [[Petrol engines intermittent 2.1|Temp sensor]] <br> | ||
[[Petrol engines intermittent 2.1|Idle Stabilisation Valve/ IS control unit]]<br> | [[Petrol engines intermittent 2.1|Idle Stabilisation Valve/ IS control unit]]<br> | ||
Fuel pressure/fuel press. reg manifold balance feed etc | |||
Over-run throttle stop adjustment (Hesitation) | |||
===Exhaust causes=== | ===Exhaust causes=== | ||
| Line 41: | Line 46: | ||
Burnt exhaust valves | Burnt exhaust valves | ||
==Stopping== | |||
Fuel starvation (electric pump/ strainer/filter/fuel gauge problem)<br> | |||
ECU malfunction (heat sensitive)<br> | |||
[[Petrol engines intermittent 2.1|Vanagon syndrome]] <br> | |||
==Bad starting== | |||
Earthing - starter/starter pinion support bush/bad starter | |||
Flooding (carb, stuck needle valve, punctured float) | |||
Flooding (injection, T2 sender, ISV) | |||
Revision as of 01:28, 1 December 2009
General advice
Replacing parts
Is usually part of eliminative diagnostics - but can catch you out.
Aidan: Just because parts are new don't assume they are good (lets face it nowadays what, if anything, is made better than it used to be). If anything is changed, especially if it's not because of a fault, keep the old part to be able to revert if necessary. This applies particularly to engine ignition components e.g. HT leads, rotor arm, etc.
General approach
A systematic and analytical aapproach from beginning to end usually pays dividends
HM: Try to work logically, and keep notes. Don't make assumptions at an early stage... do the groundwork in systematically eliminating suspected parts, systems and reasons for the problem.
Always "assumed" is the general good state of the engine internals... sound internally, with +ve evidence (e.g. compression test) must be determined before proceeding to any detailed diagnosis of ancillaries that follows.
Usually, start with fuel and sparks. Fuel usually before sparks, if nothing previously known.
New owner/new vehicle?
If the vehicle is new to you, or you haven't owned a T25 before...
HM: Don't assume anything about anything... be a pessimist, until you know better. Go back to basics and work forward
Misfiring/hesitation
Ignition causes
Aidan: Some may remember Project Caravelle had a problem once upon a time following fitting of new parts during service that he couldn't resolve and ended up throwing in the towel and selling the van at a big loss, then new owner replaced leads with a good old set and it was sorted for a tenner, just because new don't assume they are good, (lets face it nowadays what if anything is made better than it used to be) if anything is changed, especially if it's not because of a fault, keep the old to be able to revert if necessary.
HT leads, rotor arm, coil, ECU,
Carburretion causes
Weak misfire/hesitation OR grossly overfuelling (temp sender/blocked air filter, stuck choke etc) Air leaks anywhere between carb and cylinder (flanges/manifolds, vacuum pipes etc) Fuel starvation (fuel filter, tank feed blockage, pump failing)
Injection/ECU/AFM/ISU causes
Vanagon syndrome
Lambda sensor (2.1 MV)
Temp sensor
Idle Stabilisation Valve/ IS control unit
Fuel pressure/fuel press. reg manifold balance feed etc
Over-run throttle stop adjustment (Hesitation)
Exhaust causes
Leaks and holes in the standard exhaust system can result in popping back when on the overrun, and slightly weak fuel/air mixtures that may cause hesitation on light throttles. Seriouly open exhausts can cause valve burning or overheating in the longer term, and can require mixture richening/re-jetting up, to get performamnce back and prevent damage. Of the three fuelling types, the injected MVs runnning closed loop (lambda connected) should stay in tune better.
Wear/Damage/Age causes
Burnt exhaust valves
Stopping
Fuel starvation (electric pump/ strainer/filter/fuel gauge problem)
ECU malfunction (heat sensitive)
Vanagon syndrome
Bad starting
Earthing - starter/starter pinion support bush/bad starter Flooding (carb, stuck needle valve, punctured float) Flooding (injection, T2 sender, ISV)
