A friend of mine's daughter has a 1994 Suzuki Swift 1.3 Gti.
(The car has had 1 session at an engine diagnostic centre (told that was the "best bet" by a Suzuki dealer), but not tested on a rolling road. The centre didn't come up with any actual solution.)
The engine idles at the correct overall speed, but is very lumpy and the ignition timing viewed on a strobe is jittering about 5 degrees. Above about 1200 RPM the ignition timing appears stable (throttle position idle switch?) and advances correctly.
If the throttle is opened quickly, engine response is very sluggish and accompanied by a deep "throaty" noise. This is even when standing still. On the road, there is virtually no power until engine reaches approx 3000 rpm and then power returns and engine revs freely. It comes in fairly suddenly, but not like an absolute switch. The car will run along the flat or downhill in a high gear with lowish revs as normal, i.e. no bucking from the engine. But setting off from rest requires constant 3000+ rpm and loads of clutch slip, and hills require a run at them.
Full static diagnostic has been carried out and all timing, HT and emissions were OK. Leak tests have also been carried out on all inlet manifold pipes and no problems found. Chemical test on radiator coolant indicated no leaks from head gasket.
ECM code 34 (air flow sensor (AFS)) is stored in EMU, but "Check Engine" light is not on during normal running.
Restricting the air flow to the inlet port of the AFS (not the whole engine) causes engine to stall, so it appears to be doing at least some measuring. No other test on AFS carried out yet. Tests have been carried out on Throttle Position Sensor and Idle Speed Control solenoid/valve and found to be OK. EGR relay looks ok, and nipping of the EGR pipework seems to make no difference either way.
Anybody any ideas?
I'm afraid I have to go away for a couple of days now, so won't be able to answer anyone's further queries until Monday, but I thought I'd post this now then at least there's more time for people to see it. Hope that's OK. My friend may be testing more areas in between times anyway.
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COuld be AFS - monitor its output as rpm is increased.
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I don`t know the car but assuming the ecu has an advance retard.it is possible the vaccum pipe is split which will cause that problem.as I say I don`t know the car but it would be advisable to check all vaccum pipes for sign`s of damage/split`s.I have found it to be a problem on a lot of cars.Let me know
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Partially blocked exhaust? Collapsed inards in a silencer perhaps?
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My friend's made some more measurements:
Voltages measured on AFS:
Ignition on, engine stopped: 0.6V (agrees with manual)
Engine running: 1.7V to 2.3V 800 to 3000rpm
Injector signals observed with an oscilloscope:
As you open the throttle the no. of pulses increases briefly and as you close the throttle the pulses disappear. This appears to respond very quickly, but is not accompanied by an increase in engine revs.
Fuel flow rate measured: 0.5l in 10s, i.e. 3l/minute - Haynes manual states >2l/min, so looks ok.
Noted that that the fuel pressure regulator has a hole in the top with what looks like a rubber seal behind it. After start up and a few minutes of idling, there's a small, continuous fuel leak from it. This has only been happening since last Monday, so not likely the cause of any of the cause of the problem, but may be a side effect - pressure too high? Would this mean too much fuel going in at low revs, so choking it? Exhaust has a lambda sensor (but no catalytic converter) - would ECU try to do something to pull the mixture back to normal?
He may yet have to visit another fuel injection specialist centre...
Don't miss the next instalment...!
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I had exactly the same symptoms when the cambelt on my nissan was fitted incorrectly (timing wandering about no power)...Could be yours is out a tooth or two if it's fitted with a cambelt or a faulty crankshaft position sensor or even the crankshaft pulley has worked loose.
hope this helps
steve
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You were correct Dieselhead - the problem was effectively an incorrectly-fitted crank pulley. I'd wondered about this myself but assumed that when the car had been to at least 2, possibly 3 diagnostic centres and each had proclaimed the ignition and valve timing correct, that that possibility had been investigated. Turns out none of them tried the old 'screwdriver down the spark plug hole to check TDC' test!
The whole valve timing was retarded by up to about 10 deg relative to the crankshaft due to a worn keyway on the crankshaft end pulley. A HOME-MADE key was found to be in there, and it seems likely that if it was not a good fit in the first place, an initial bit of slopping about had gradually caused the keyway to wear, causing more slap when going on and off the power, causing more wear, and so on.
The pulley is in 2 parts - the first part is keyed into the end of the shaft and held on with a single central nut. The next part is bolted onto the first with 5 screws. You'd actually only need to remove the outer part to change the cambelt, but my friend suspects that the whole pulley was removed when the belt was last changed, and the key lost during the process, leading to the home-made one being substituted!
The keyways in the pulley and crankshaft were built-up again using some proprietary quick-hardening epoxy metal putty stuff and on reassembly the engine ran correctly again!
There had already been a clue when one of the diagnostic centres measured unusually low vacuum in the inlet plenum (but they didn?t get any further diagnosing a cause) ? I guess the exhaust valve would still be open a bit (too long) during the induction stroke and the inlet valve during the compression stroke. Isn?t hindsight lovely.
And no, he didn't even take it straight back down the auction - it's back in use by his daughter.
We'll see whether the fix holds-up!
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I doubt a worn keyway in crank more likely to be wrong size key fitted allowing free play on crank/pulley tis also not likely a home made one will work.Due to torgue on crank.it only takes a key that is a few thou out of thickness to cause it.still should not have happened.still good luck
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