Corvette 1990 problem.
Thread Starter
Intermediate
Joined: Oct 2002
Posts: 32
Likes: 0
From: Karlskoga 02
Corvette 1990 problem.
Last summer i bought my self a Corvette 1990. (L98 350 TPI, 6-shifted manual transmission)
The car seems pretty much original except the exhaust pipes.
As long as i've owned the car it's been bugg'n me :(
My problem is pretty much the following:
* Sluggish at low RPM's and at idle.
* Even more sluggish when entering closed loop.
* Sometimes it backfires when shifting during inspired driving.
(This also happens sometimes when i quickly rew the engine in "neutral")
Stuff that's been tested and has been changed.
* Ignitionwires & spark plugs (Checked behavour in darkness)
* New Lambda/O2 sensor
* Ignition module
* New fuel filter
* fuel pressure
* New Fuel pressure regulator
* Vacuum-hoses conserning MAP & fuel pressure regulator
* Tested Compression at all cylinders.
* Distributor has been checked a bunch of times.
* Checked for intake leaks.
* Original Chip
* No error codes
* EGR-solenoid checked
* Tested with other ECM
* New EGR-valve
* New MAT-sensor
* New MAP-sensor
At idle my BLM says: 108
Maximum reducement of fuel?
All hint's are welcome!
The car seems pretty much original except the exhaust pipes.
As long as i've owned the car it's been bugg'n me :(
My problem is pretty much the following:
* Sluggish at low RPM's and at idle.
* Even more sluggish when entering closed loop.
* Sometimes it backfires when shifting during inspired driving.
(This also happens sometimes when i quickly rew the engine in "neutral")
Stuff that's been tested and has been changed.
* Ignitionwires & spark plugs (Checked behavour in darkness)
* New Lambda/O2 sensor
* Ignition module
* New fuel filter
* fuel pressure
* New Fuel pressure regulator
* Vacuum-hoses conserning MAP & fuel pressure regulator
* Tested Compression at all cylinders.
* Distributor has been checked a bunch of times.
* Checked for intake leaks.
* Original Chip
* No error codes
* EGR-solenoid checked
* Tested with other ECM
* New EGR-valve
* New MAT-sensor
* New MAP-sensor
At idle my BLM says: 108
Maximum reducement of fuel?
All hint's are welcome!
Drifting
Joined: Mar 2001
Posts: 1,636
Likes: 3
From: Lafayette IN
Re: Corvette 1990 problem. (dahlman)
"distributor has been checked" Including the pickup coil? Had some problems with mine. A newer one gave me more probs. Also, if the previous owner was running around with bad wires for a while, it could have taken out the coil. Or at least that's why I think I took out some of mine in the past. I can't stand the 7 90's and one straight supplied with most wiresets.
Correct about 'max reduction of fuel trying to take place'.
Some basic thoughts...
"more sluggish entering closed loop" and "sluggish at low RPMs and idle".
Canister purge system or PCV setup? Had problems in mine and I got a big gush of fuel under tip-in conditions. I don't *think CCP is activated under idle though.
Are you pulling good vacuum at idle? Do you keep good fuel pressure when pump stops running/engine off (i.e. any leakdown)?
Take it all with a grain of salt. My electrical knowledge is becoming slimmer by the day.
Correct about 'max reduction of fuel trying to take place'.
Some basic thoughts...
"more sluggish entering closed loop" and "sluggish at low RPMs and idle".
Canister purge system or PCV setup? Had problems in mine and I got a big gush of fuel under tip-in conditions. I don't *think CCP is activated under idle though.
Are you pulling good vacuum at idle? Do you keep good fuel pressure when pump stops running/engine off (i.e. any leakdown)?
Take it all with a grain of salt. My electrical knowledge is becoming slimmer by the day.
Burning Brakes
Joined: Sep 1999
Posts: 786
Likes: 31
Cruise-In II Veteran
Re: Corvette 1990 problem. (dahlman)
Just some guesses: Fuel injectors? You mentioned a BLM of 108, which would indicate rhe computer is trying to compensate for a rich mixture. I would suggest the following:
1. Check the resistance across the connectors of each injector with a digital ohmmeter. You should see something form 11 to 18 ohms. In my opinion an 11 ohm reading is very marginal. Higher is better. This test will give you some idea as to the electrical health of the injector but not the mechanical health. (if the insulation on the internal windings of the injector breaks down, the ohm reading will decline. No resitance=no magnetic field to "fire" or activate the injector to spray fuel.).
2. Do a visual inspection of your spark plug electrodes. Are they black and soot covered indicating a rich mixture? Or maybe just one or two are showing an over rich condition. Those cylinders would most likely be the ones with the bad injector(s).
3. Sometimes the "Instant Mile Per Gallon" readout on the instrument panel will give a clue as to the health of the injectors. This happens when a leaky injector dumps excess fuel into the induction system and the O2 sensor sees this rich mixture. The computer will then cut back on the open cycle time of ALL the injectors to try and get the engine back to the proper O2/fuel ratio.
The "Instant MPG" is calculated from the injecter pulse (open) time. Thus when the pulse time is cut back the computer thinks the car is using less fuel and getting some outrageous fuel mileage like 50-60 mpg! It isn't but the GIGO theory takes over (Garbage in=Garbage out)
4. Failure of injectors is very common on the 1990, especially after 50-70,000 miles.
Just some ideas!
1. Check the resistance across the connectors of each injector with a digital ohmmeter. You should see something form 11 to 18 ohms. In my opinion an 11 ohm reading is very marginal. Higher is better. This test will give you some idea as to the electrical health of the injector but not the mechanical health. (if the insulation on the internal windings of the injector breaks down, the ohm reading will decline. No resitance=no magnetic field to "fire" or activate the injector to spray fuel.).
2. Do a visual inspection of your spark plug electrodes. Are they black and soot covered indicating a rich mixture? Or maybe just one or two are showing an over rich condition. Those cylinders would most likely be the ones with the bad injector(s).
3. Sometimes the "Instant Mile Per Gallon" readout on the instrument panel will give a clue as to the health of the injectors. This happens when a leaky injector dumps excess fuel into the induction system and the O2 sensor sees this rich mixture. The computer will then cut back on the open cycle time of ALL the injectors to try and get the engine back to the proper O2/fuel ratio.
The "Instant MPG" is calculated from the injecter pulse (open) time. Thus when the pulse time is cut back the computer thinks the car is using less fuel and getting some outrageous fuel mileage like 50-60 mpg! It isn't but the GIGO theory takes over (Garbage in=Garbage out)
4. Failure of injectors is very common on the 1990, especially after 50-70,000 miles.
Just some ideas!
Thread Starter
Intermediate
Joined: Oct 2002
Posts: 32
Likes: 0
From: Karlskoga 02
Re: Corvette 1990 problem. (HighHopes85)
Thank's a bunch guys!
"Do you keep good fuel pressure when pump stops running/engine off (i.e. any leakdown)?"
What's considered normal?
Should the OFF-pressure maintain like 41 PSI?
Are we speaking about hours or minutes here?
I think i would need some basic guidlines about this issue. :)
"Do you keep good fuel pressure when pump stops running/engine off (i.e. any leakdown)?"
What's considered normal?
Should the OFF-pressure maintain like 41 PSI?
Are we speaking about hours or minutes here?
I think i would need some basic guidlines about this issue. :)
Thread Starter
Intermediate
Joined: Oct 2002
Posts: 32
Likes: 0
From: Karlskoga 02
Re: Corvette 1990 problem. (dahlman)
Another thing.
I have 8 new Ford SVO #24's.
Do you guys think it's possible to make my car run smooth with theese only by adjusting the Prom injector constant?
I have 8 new Ford SVO #24's.
Do you guys think it's possible to make my car run smooth with theese only by adjusting the Prom injector constant?
