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88 900 SPG, 141k miles
I have a hesitation, bucking, surging at low rpm, "trailer-hitching", more pronounced on hills and when giving lots of gas. Goes away or is hidden at higher rpms, above 3000 - 3500 rpm. Worst when first started, but always very noticible.
I've done the usual tune up and now just had it to a shop specializing in Saabs (former dealer mech.). Here's whats been done...
NGK plugs (bcp 6es) gap at .025
bougicord wires
bosch cap & rotor
fuel filter
timing at 16 degrees
base boost at 5-6 lbs, max boost 15 lbs
AMM swapped with known good one, no change
turbo bypass valve verified ok
O2 sensor hooked to scope, within range while idling and during test drive while surging. Engine not lean or rich during this test so fuel pressure and injectors ruled out.
Cylinder balance test OK, hooked to diagnostic equipment that takes power from one spark plug at a time, proves each cylinder (spark and fuel) is working.
Vacuum advance ok
Vacuum at idle ok, no leaks.
Coil tested ok.
Hooked to 5 gas analyzer, all gases very good, within range.
Compression 147 - 155 all cylinders
I ran strong fuel injector cleaner through - no difference. I ran octane booster through - maybe slight difference, probably just masking the problem.
Mechanic thought it odd that timing mark jumps about 5 degrees when reading with the timing light. In other words, timing mark is more of a blur than a rock steady line. He suggested looking further at timing chain, cam gears, chain tensioner, etc. I think it may have always looked like this, not sure. Chain, tensioner, and guides were done 35k miles ago. I pulled valve cover last night; flywheel TDC mark and cam marks line up perfectly, gears look tight and fine, chain looks normal. Chain guides look fine, no noticible wear. Chain tensioner very hard to see, I don't think it is extended far but can't verify. No chain slack under the cam gears (between crank and cams). Between the cam gears chain has a little slack but this depends on how you turn the engine. I'm guessing thats normal.
I kept thinking fuel injectors. What if one were bad. Mechanic says this would show up as lean or rich condition or show up on cylinder balance test. Both of which were fine.
My modifications: 3 bar fuel pressure regulator, k&n filter, 20lb turbo bypass valve, boost to 15, low restriction exhaust.
I can't throw any more money at diagnosis! I really need some good suggestions. This is killing me.
A.Roper
88 SPG 141k miles
, Wed, 27 Jun 2001 14:34:45
, Wed, 27 Jun 2001 10:27:51
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