123 Last
Item Posts    Sort Order

Ruff idol, won't run past idol without the engine dying. 90 Corvette

 
JW72
I love my Chevy Chevette!
Posts: 21
Joined: 03/14
Posted: 03/20/14 12:23 PM

Ruff idol, won't run past idol without the engine dying.  Rev engine, engine strains to increase rpms.  Like there is a loss of horse power or no horse power.  Reaches 1,500 rpm, tries to die, pump the throttle to keep the engine running.  Engine has a noticeable miss at idol and rpms.  

Driving is limited to 1,500 in any gear, more rpm and engine dies.  Mechanic looked at the Corvette, "Its either the CPM or the distributor", he could not check either or didn't want to.

Where to start as there are so many areas that could cause this problem.  CPM does have an after market chip.

I do have many, many years of being an expert shade tree mechanic, like to do my own repairs.

JW  
Retired, raced Corvettes in SCCA for 20 years. Own a 1990 Corvette and a 1979 Corvette.

Post Reply
wayne712222
My first time was in a Chevy
Posts: 140
Joined: 10/13
Posted: 03/20/14 03:16 PM

start with some of  the info here..

http://forums.corvettefever.com/70/8585187/c4-corvettes/which-used-scan-tools-for-82-to-94-corvettes-with/

i would first change the fuel filter.. if it's clogged.. then you will need to check the fuel pressure or the amp draw of the fuel pump..  even listen to the fuel pump.. is it noisy??? it probably needs changing.. and you don't have to drop the tank on a C4.. the whole hanger comes out in under 30 minutes thru the rear deck..  really easy..

with the scan tool are there any codes..

please post if you own a scan tool that will work with your scan tool ..


please post the info if you have a digital volt meter..

please post if you have one of the little harbor freight circuit tester that measure amp draw??? these are great for checking fuel pump amp draw..

i can also describe how to check your distributor your self.. its not hard...  

Post Reply
wayne712222
My first time was in a Chevy
Posts: 140
Joined: 10/13
Posted: 03/20/14 03:40 PM

thats strange the 1990 motor still used the big cap distributor..


Untitled4 Zpsec225251

Untitled19 Zpscaa09511

Untitled18 Zps37da024d


Untitled5 Zps63341c9b

Untitled3 Zpsb7fb0c42

Untitled7 Zpsb4b38f49

Hei 4Pinmodule Zps5e505aa8

88 C4 Terminalblockbehindbattery Zpsc49dc171

while you are back in there cleaning the power distribution stud..

please see if you can find the thin wire from the negative cable to the firewall beside or behind . you can see this rusty ground location screw...

87 C4 Underbatterygroundconnection

please.. perform this voltage drop test..

Voltagedroptesting  

Post Reply
wayne712222
My first time was in a Chevy
Posts: 140
Joined: 10/13
Posted: 03/20/14 03:45 PM

can you post more info...

pictures from around the engine compartment.. use photobucket.  paste links here.

video that you upload to youtube..  paste the link here  

Post Reply
wayne712222
My first time was in a Chevy
Posts: 140
Joined: 10/13
Posted: 03/20/14 10:12 PM

one thought... please disconnect the power brake booster vacuum hose and plug it..  so there is no vacuum leak to the motor..

see if it dies then.. perhaps the brake booster is blown and leaking vacuum..

that would cause a rough idle and stalling as the idle air control motor could not back far enough out to compensate for a massive vacuum leak.

lets look at the throttle body...

engine off.. grab the throttle lever.. open it slightly..  see if it wiggles around in the throttle shaft bore..  L98 and Throttle body fuel injected motors both have this same issue..  the throttle shaft bore wears into an oval.. this allows the shaft to move forward and back... this effects the tiny angle the throttle lever closes to.. that effects the TPS voltage.. L98 motors like to have the closed TPS voltage at EXACTLY 0.53 volts DC when checked with a scan tool .. if you sit in the car looking at the live data .. and you operate the throttle pedal several times.  it should return to the exact same fraction of a volt.  if it does NOT return to the exact same fraction.. the computer thinks you have your foot on the throttle and are raring to go someplace.. so it will keep the computer program out of idle fuel control..  the fuel injector pulse width will stay above 2.1MS..  

look for
engine warmed up fully..

ECT 190F to 230F normal temps on C4's are up to 239F.

TPS at 0.53 Volts DC... each time returns to this fraction ..

IAC .. 20 to 50 at idle..

injector pulse width.. 1.2 to 1.4MS..  at idle..

post your data values.. i will have a look at them and see if i find any issues..  i am really good at this..

look at the data stream with a 1990 C4 going about 60MPH...

C4livedata Zpsad4aa4a5  

Post Reply
JW72
I love my Chevy Chevette!
Posts: 21
Joined: 03/14
Posted: 03/21/14 11:31 PM

The Corvette was stored off and on.  I'm the third owner.  I have replaced the brakes, fuel filter, spark plugs and have had the smog system gone through.  Had a smog problem, smoking engine.  The complete system was replaced.  Smoking stopped, increase in HP.  After new spark plugs, increase in HP and power range.  

Yes I have all the tools you mention except for a scan tool.  Not sure which one to buy.

Check wires to see if all eight cylinders were working, all O.K.

Listen to fuel injectors, all are clicking away.

Compression test, 158 -165 per cylinder.

Corvette 1990 41,200 original miles.

Have a set of fuel injectors to install.

I have a couple of HEI left over from racing.

Have the stock Eprom, but I can't seem to find it.

All of the other items that you mentioned I will look into, will take me some time.

Thank you for your help, I really appreciate it !!!!

JW  
Retired, raced Corvettes in SCCA for 20 years. Own a 1990 Corvette and a 1979 Corvette.

Post Reply
JW72
I love my Chevy Chevette!
Posts: 21
Joined: 03/14
Posted: 03/21/14 11:33 PM

Crazy  
Retired, raced Corvettes in SCCA for 20 years. Own a 1990 Corvette and a 1979 Corvette.

Post Reply
wayne712222
My first time was in a Chevy
Posts: 140
Joined: 10/13
Posted: 03/22/14 12:18 AM

which scan tool????

which area of craigslist do you live near.. i don't want you address. i can look up and paste scan tools from nearby areas to you to look at..

the actual best deal if you have OBD2 cars is really the OTC3499N kit.. but its just under 500 bucks.. but it will do amazing things on more years of cars.. 82/83 to current models.

vacuum advance HEIs will NOT work on this..

these have a screw down cap not a latch down as i recall.. i could be wrong.. .. electronic spark timing..  no mechanical advance..

they will also have an 7 pin HEI module.. where vacuum advance versions will have a 4 pin module..

the only things that might fit are the ignition coils and if its a race coil.. the primary resistance might be too low for the 7 pin module to switch properly..

less resistance causes more amps to be drawn in when the power transistor is switched on to ground to saturate the primary windings..

you could also .. have a BLOCKED exhaust.. clogged cat.


with a vacuum gauge hooked to the intake manifold vacuum port.. slowly raise the engine speed.. the intake manifold vacuum should NOT DROP.. it should stay steady or rise..

you can also pull the oxygen sensor and see if it accelerates harder.. warning. there will be FLAME coming out that hole..  and you can burn the spark plug wires.. or sensor wires..  what ever is NEAR the exhaust blast when you start it up.  

Post Reply
JW72
I love my Chevy Chevette!
Posts: 21
Joined: 03/14
Posted: 03/22/14 11:07 AM

Wayne,

I live in Sacramento, Ca

I do not have a clue about OBD's.  I read that OBD2 are for cars 1992 and above.  ODB1 are for cars 1991 and later. Reluctant to purchase anything that is too expensive for this Corvette.  This will be a one time expense, for this Corvette only.    

Replaced HEI cap, with coil, and the internal electronics. My racing HEI's don't have a vacuum.  No change.  

EGR and hose, PVC, IAT sensor, replaced 10/24/2013

Actually have a Noid test kit, all fuel injectors test O.K.

Somehow, I believe that there is a sensor that is not working correctly.  My lack of knowledge is MY problem.

Where is the exhaust Cat ?  Can I remove and clean or just replace ?

Looking for a book that will explain the TPI with diagrams.

Future plan is to replace all fuel injectors and install a fuel gauge in the fuel rail or line.

I studied your example of a readout for an Eprom.  Like I understand what I am looking at  Confused

Again, thank you for your time and effort for my problem.  Talk to you soon.

JW  
Retired, raced Corvettes in SCCA for 20 years. Own a 1990 Corvette and a 1979 Corvette.

Post Reply
JW72
I love my Chevy Chevette!
Posts: 21
Joined: 03/14
Posted: 03/22/14 11:18 AM

Wayne,

The disappointment in a 1990 Corvette is the lack of HP. The engine is rated only at 245HP, after 4,500 rpm the HP curve is flat.  I am used to Corvette's with at least 350 HP and a red line of 6,500 or better.

The 1990 Corvette handles like a race car in the 80's -90's.  Easy to introduce oversteer only to run out of engine.  

JW  
Retired, raced Corvettes in SCCA for 20 years. Own a 1990 Corvette and a 1979 Corvette.

Post Reply
JW72
I love my Chevy Chevette!
Posts: 21
Joined: 03/14
Posted: 03/22/14 11:44 AM

Wayne,

Looked up some OBD code readers.

AutoXray CodeScout OBD I & OBD II Code Reader AX2500

Craftsman 20899 CanOBD2&1 Diagnostic Scan Tool with Live Data

502 1 6 Discs OBD 1 2 CAR ELM327 DIAGNOSTIC SOFTWARE ECU REMAPPING TUNING OBD I needs adaptor.

Above located on eBay

Checked Craig's List, To many for me to understand.

JW  
Retired, raced Corvettes in SCCA for 20 years. Own a 1990 Corvette and a 1979 Corvette.

Post Reply
wayne712222
My first time was in a Chevy
Posts: 140
Joined: 10/13
Posted: 03/22/14 04:34 PM

AutoXray CodeScout OBD I & OBD II Code Reader AX2500   possible.. i have to look this one up.. i have an earlier model that works great..

Craftsman 20899 CanOBD2&1 Diagnostic Scan Tool with Live Data NOPE.. this is an innova.. worthless for other than trouble codes and you can get those with a 6 cent crimp connector..  or a chunk of wire.

502 1 6 Discs OBD 1 2 CAR ELM327 DIAGNOSTIC SOFTWARE ECU REMAPPING TUNING OBD I needs adaptor.

this is interesting.. do you have a PC laptop running windows 98 or i forgot the other version.. that it works with.. microsoft  just ended support for those and are forcing everybody to update to NEW computers that run windows 7 or 8..  so none of your early programs that you use everyday will work any more..  

makes me want to pound my head into a block wall.

at least car manufurer's dont discontinue parts.. oh wait they do..

ford when my grandfather worked there..  bulldozed a massive warehouse of ford parts into LA harbor..  it was cheeper to bull doze them than to ship them  back to other factorys for melting.

somebody got greedy at GM .. found out there is $0.05 worth of gold in the PROM chips..   sold all the gm prom chips and tooling for scrap..   does not matter that when you needed on. you had to pay them 50 to 80 bucks each for it..  instant gratification..

here one...
http://orangecounty.craigslist.org/tls/4309210662.html  

Post Reply
wayne712222
My first time was in a Chevy
Posts: 140
Joined: 10/13
Posted: 03/22/14 04:48 PM

here is another..
http://inlandempire.craigslist.org/pts/4380135843.html



this is intersting..

http://www.ebay.com/itm/GM-OBD1-Scanner-Cable-Software-USB-to-12-pin-ALDL-direct-GM-OBDI-/111245393571



http://www.ebay.com/itm/OTC-3499N-ScanPro-Elite-Code-Reader-Scanner-OBD-1-OBDII-OBD-II-2-/350975757335  

Post Reply
wayne712222
My first time was in a Chevy
Posts: 140
Joined: 10/13
Posted: 03/22/14 04:56 PM

http://www.aldlcable.com/

interesting..  

Post Reply
JW72
I love my Chevy Chevette!
Posts: 21
Joined: 03/14
Posted: 03/22/14 11:20 PM

Wayne,

Been doing my homework and have come up with a possible plan for diagnostic software.  
I have a laptop and a Android tablet.  Looked at some diagnostic software. TunerPro supports many vehicle makes and models, including GM OBDI (pre-96). Http://www.tunerpro.net/screenshots.htm  

       ALDLdroid is an application for OBD1 GM (ALDL) ECM. It is currently compatible with both 160 baud and 8192 baud ECM's.  Http://aldldroid.android.informer.com/  

       Need to purchase ALDL OBDI to USB cable, which I am haviing trouble finding, OBDII ? tons available.

       My laptop is several years old, Window XP, Android tablet is new.  The TurnerPro software is very extensive and comprehensive.  

I do not think that there is a problem with the ECM or the Eprom.  I can't tell you why I believe this, just a hunch.  If it is the ECM, I have collected information on where I can purchase a refurbished ECM.

My biggest problem is keeping the engine running as I check things in the engine compartment.

Your thoughts on the above ?  
Retired, raced Corvettes in SCCA for 20 years. Own a 1990 Corvette and a 1979 Corvette.

Post Reply
123 Last
TO TOP