what your 100% sure is correct may not be!
I recently had a guy over to do a minor test & tune on his car,(name with -held due to protecting the guys good name )no hes not on this site hes a neighbor) (an 1985 vette) because it didn,t run very well, (It idled like crap,after a cam upgrade)now it had a fairly normal low rpm power curve but it failed to pull well after about 3500 rpm
he was convinced it was an injector issue and wanted me to test and replace the injectors if required, or that the cam he had installed was defective
I told him the first step was to DROP BACK TO THE BASICS
and verify everything as we proceeded
but he was 100% convinced he had done every step in the cam install correctly, and wanted me to concentrate on finding the defective injector(s).
step one
I verified his engines TDC on the timing tab and damper
(the result was that the damper marks were off by about 4 degrees) I asked if he had degreed in the cam (knowing the obvious answer)
then I installed an adjustable timing tab and told him he was required to buy a replacement functional damper
STEP TWO
I suggested we adjust the ignition timing , and we got that correct to factory specs
STEP THREE
I suggested we adjust the valves,(he was 100% convinced he had that correct)
well I pulled the valve covers which is not easy with the alternator in the way) and after adjusting them at idle found they were all over the map on preload, (some were 1/4 turn in from zero lash some were 1.5 full turns in) he had adjusted them by spinning the push rods between his fingers, feeling for resistance after seeing the intake valve close., and I noticed one valve spring was cracked,(replaced that but had to use a stock spring so I strongly suggested he buy a full new set, I looked up the correct part number (YEAH! I KNOW! the chances he,ll follow thru and buy and install them are about as good as my wife buying me a MISTRESS for my birthday)
STEP FOUR
once the valves and timing were adjusted I checked for fuel pressure and found, that the fuel pressure was 36 lbs but dropped rapidly if the engine was shut off, it turned out the 9th injector was leaky(luckily I had a spare from a salvage yard)
step five
I checked for vacuum leaks and found the lower left runners were not sealed correctly(that was corrected with a new gasket.
step six
I metered the ignition wires for resistance (they all sucked)and checked the firing order,(ok) looked over the rotor and distributor cap (absolute joke, corroded, (white crumbly aluminum contacts) looked to be several years old and evidence of getting wet at times) and verified plug gap (again they ran from .037-.051) I dropped them all to .043, now the car ran a good bit better, we discussed pulling the timing cover and verifying the cam timing but that's a good deal more work, so for now we will assume its close until we get the time to check
step seven
I started verifying battery voltage, fluid levels, and sensor connections , and found the o2 sensor wire had obviously been at least on occasion touching the exhaust in the past as it was floppy loose ,as the insulation was melted, and the knock sensor was not even connected as the wire that goes to it had no connector.
if you think this was a worse case deal its not!
most older corvettes I see and some I work on, come into the shop only after the owners get tired of chasing intermittent problems, or find that the car runs like crap and only then decide to research the cause.
look we all have problems,wear issues and most of us work on very tight budgets, but you can,t jump to conclusions or assume anything, the only way to correct problems is to drop back to the basics and VERIFY every thing STEP BY STEP,WITH A BASIC CHECK LIST and a few tools like a timing light, a shop manual and a MULTI meter are mandatory
http://forum.grumpysperformance.com/viewtopic.php?f=32&t=1401
http://forum.grumpysperformance.com/viewtopic.php?f=50&t=609
http://forum.grumpysperformance.com/viewtopic.php?f=32&t=2697
http://forum.grumpysperformance.com/viewtopic.php?f=32&t=168
http://forum.grumpysperformance.com/viewtopic.php?f=70&t=875
http://forum.grumpysperformance.com/viewtopic.php?f=62&t=882&p=1390&hilit=+propane+leaks#p1390
I recently had a guy over to do a minor test & tune on his car,(name with -held due to protecting the guys good name )no hes not on this site hes a neighbor) (an 1985 vette) because it didn,t run very well, (It idled like crap,after a cam upgrade)now it had a fairly normal low rpm power curve but it failed to pull well after about 3500 rpm
he was convinced it was an injector issue and wanted me to test and replace the injectors if required, or that the cam he had installed was defective
I told him the first step was to DROP BACK TO THE BASICS
and verify everything as we proceeded
but he was 100% convinced he had done every step in the cam install correctly, and wanted me to concentrate on finding the defective injector(s).
step one
I verified his engines TDC on the timing tab and damper
(the result was that the damper marks were off by about 4 degrees) I asked if he had degreed in the cam (knowing the obvious answer)
then I installed an adjustable timing tab and told him he was required to buy a replacement functional damper
STEP TWO
I suggested we adjust the ignition timing , and we got that correct to factory specs
STEP THREE
I suggested we adjust the valves,(he was 100% convinced he had that correct)
well I pulled the valve covers which is not easy with the alternator in the way) and after adjusting them at idle found they were all over the map on preload, (some were 1/4 turn in from zero lash some were 1.5 full turns in) he had adjusted them by spinning the push rods between his fingers, feeling for resistance after seeing the intake valve close., and I noticed one valve spring was cracked,(replaced that but had to use a stock spring so I strongly suggested he buy a full new set, I looked up the correct part number (YEAH! I KNOW! the chances he,ll follow thru and buy and install them are about as good as my wife buying me a MISTRESS for my birthday)
STEP FOUR
once the valves and timing were adjusted I checked for fuel pressure and found, that the fuel pressure was 36 lbs but dropped rapidly if the engine was shut off, it turned out the 9th injector was leaky(luckily I had a spare from a salvage yard)
step five
I checked for vacuum leaks and found the lower left runners were not sealed correctly(that was corrected with a new gasket.
step six
I metered the ignition wires for resistance (they all sucked)and checked the firing order,(ok) looked over the rotor and distributor cap (absolute joke, corroded, (white crumbly aluminum contacts) looked to be several years old and evidence of getting wet at times) and verified plug gap (again they ran from .037-.051) I dropped them all to .043, now the car ran a good bit better, we discussed pulling the timing cover and verifying the cam timing but that's a good deal more work, so for now we will assume its close until we get the time to check
step seven
I started verifying battery voltage, fluid levels, and sensor connections , and found the o2 sensor wire had obviously been at least on occasion touching the exhaust in the past as it was floppy loose ,as the insulation was melted, and the knock sensor was not even connected as the wire that goes to it had no connector.
if you think this was a worse case deal its not!
most older corvettes I see and some I work on, come into the shop only after the owners get tired of chasing intermittent problems, or find that the car runs like crap and only then decide to research the cause.
look we all have problems,wear issues and most of us work on very tight budgets, but you can,t jump to conclusions or assume anything, the only way to correct problems is to drop back to the basics and VERIFY every thing STEP BY STEP,WITH A BASIC CHECK LIST and a few tools like a timing light, a shop manual and a MULTI meter are mandatory
http://forum.grumpysperformance.com/viewtopic.php?f=32&t=1401
http://forum.grumpysperformance.com/viewtopic.php?f=50&t=609
http://forum.grumpysperformance.com/viewtopic.php?f=32&t=2697
http://forum.grumpysperformance.com/viewtopic.php?f=32&t=168
http://forum.grumpysperformance.com/viewtopic.php?f=70&t=875
http://forum.grumpysperformance.com/viewtopic.php?f=62&t=882&p=1390&hilit=+propane+leaks#p1390