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87 Vette Stalls randomly....otherwise runs good

 
87L98Vette
I love my Chevy Chevette!
Posts: 14
Joined: 06/10
Posted: 06/19/10 06:22 PM

Hi guys,
I have an '87 Vette..L98 A/T 45,000 miles. It's a well maintained..clean car from Northern California, very original with no modifications.
Lately it has started to stall in traffic..it quit once on the freeway, and sometimes will stall shortly after it's first started in the morning. I did notice that the check engine light will flash while it's about to stall,it doesn't stay on or leave a code. The car always starts right up after I let it set for a minute or two. I have done all of the basic checks..ignition and fuel systems are good and the MAF is new. Otherwise the car runs very good and has been very dependable. I did pull the ECM down and check the harness connections..I also pulled the PROM out and snapped it back in to make sure that wasn't the issue.
Not sure where to go next..maybe someone has already run into this and can offer some advice.
Thanks.....  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 06/19/10 07:18 PM

is the fuel pump noisy??????   ever changed it?????  its over 24 years old...

takes about an hour to do it from the top....  cost about 100 bucks..  do it your self ...

every C4 owner should know how to do it..     right through the gas cap area... after you take the door frame off..  and pull the drain boot...

be sure to order a ac delco. G1 gasket.. yes G1 is the part number.. it is the proper gasket for corvette fuel tanks.. it does not come in most replacement electric fuel pumps... the strainer is also separate...

put in a new fuel filter also....


stop by a radio shack... pick up a bag of rare earth magnets.. drop some in the tank.... it will pull any sediment to them.. keep it out of the strainer and filters...  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 06/19/10 07:30 PM

other things to check...

take the cap and rotor off....   with a bright flash light..  look at the pick up coil ...     is the connector grease where it plugs in the end of the module.. green in color..   it so.. you might need a new pick up coil...  the green in the grease indicates the copper wire is dissolving..

also look carefully at the stack of parts in the pick up coil...  the top layer is cast...  the second layer is a ceramic ring magnet...

these fail from thermal cycling...  when they break...  and they do.. it can create stalling problems...

when you take the rotor off.. you might also look on the underside... make sure it has not started to burn through..

pull the coil cover off the top of the cap.. look at the round part of the coil where it is close to the coil frame...   if it is showing white circular dust patterns.. with white dots .. the coil needs replacing..


lately.. i have had to change a LOT of pick up coils... even more ignition coils...   every one gets a new rotor...   many get new caps...

don't forget to change the ground strap that fits under the coil to the new cap..

if the 3 wire harness to the side connectors on the cap is bad.. most parts stores have that in stock.. they call it an hei capacitor with harness..  be sure that the hold down screw gets properly tightened..  

it is the return for the high voltage spark..  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 06/19/10 07:33 PM

oh... and an even easier thing... change the oil pressure sending unit..

the fuel pump is controlled by it..  yep..

one wire for the gauge...  2 wires for the fuel pump...  totally isolated from each other.. but still in the same switch..


takes a special socket for the oil pressure switch.. some parts stores have loaner tools..  the sockets are cheep usually under 10 bucks..  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 06/19/10 07:36 PM

sorry for the 3 different areas to look in..  but these are the failure areas..

do you have access to a scan tool...  

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87L98Vette
I love my Chevy Chevette!
Posts: 14
Joined: 06/10
Posted: 06/20/10 07:48 AM

Thanks for all of the info. Fortunately I spent most of the late 80's & early 90's as a Tech in a small repair garage and had allot of experience with GM vehicles and OBD..but I moved into luxury imports and lost most of my "knowledge".

The Fuel pump sounds great..I thought about this as well. I can tell you that the vehicle will start and run with the Fuel pump relay disconnected..so I kind of ruled out the relay,pump and the oil pressure circuit. But maybe I'm wrong.

I did a complete ignition check and replaced the cap/rotor with Delco parts. The coil looked good..I pulled the igntion moldule and the pins were clean and I replaced the grease under it.

However this morning I went and checked for codes and found it had stored a code 51..this car has California emissions but now it's in Ohio,so I am thinking of installing a Hypertech Prom for better performance. A code 51 would seem to indicate that either the Prom or the ECM is on it's way out ?  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 06/20/10 08:29 AM

i would think a swap of the oil sending switch.. if it is a 3 wire version would be the first thing..  how about using the stethoscope on the gas filler neck... the pump is mounted directly on that hanger... see ifs its a nice steady even hum... or does it sputter every once in a while...


there have been other problems with the late 80s ECMs failing.. currently..

here is a site with the code charts...

http://www.fastbird93.com/Diagnostics.htm


got time to ohm the injectors.. there have been a bunch of them with lower resistance than spec and pulling to many amps through the ECM..

in your tool box at work...  do you have  a DSO... digital storage scope?? and a low amp current probe...    if you do..  you can test the fuel pump with the engine running.. and probably the injector amp draws also...

can you pull the ecm one more time?????   make sure the chip is properly seated... no pins bent.. just missing.. its really easy to ***

A1 cardone .. the rebuilder back east has a big stock of factory eproms they pull from the cores they buy complete...  

i take it that you have ondemand at work...  see whats the newest prom for your app... order a replacement from cardone... its on the last page of their printed ECM catalog...

this gives you a back up...   i think the reman ECMs were under 100 bucks for that model..

i normally pull the ECMs and open the case.. i examine the solder joints... i have sometimes had to resolder 300 places... to make me happy.. i am talking 2 hours with a fan blowing away the fumes.. but they work when i am done.... i resolder a LOT of circuit boards on various things on cars.. from honda main relays.. to ecms..

i cure a lot of unfixable cars... with a few hours on the work bench..

i even did one of the 98 gm ecms the other day...  cured the intermittent problems.. i did an 84 crown vic that had a weird intermittent stumble under cruise... the other mechanics told him to scrap the car.. its unfixable..  

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87L98Vette
I love my Chevy Chevette!
Posts: 14
Joined: 06/10
Posted: 06/20/10 06:37 PM

Ok...what if i bypass the oil switch and just jump the circuit to see if it still continues to stall..any harm in that ?  I did put my ear on the tank when the car was running and the pump sounded nice and strong..it runs good under load and at higher rpm's which is usually when a weak pump will show itself.I kind of ruled it out since the car had low miles and was from Northern California..which usually isn't as hot as Southern Cali. I do agree that pulling the ECM case and going over the board is a good idea..I do allot of that at work on our test equipment in the lab.
The oil pressure is two seperate units...a one wire can for the gauge and what looks like a two wire switch for the pump ? I started running 10w40 oil for the summer and that's about when this started.. I wonder if I blew the little diaphram in the switch ?

Anyone have a preference on Performance Chips ? Hypertech vs JET ?  The Hypertech chip is on backorder so I was going to go with the JET.  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 06/20/10 08:48 PM

i have not tried any of the chips...  personally...

since you have the ability to resolder the ECM.. start there..

yes you can jump the oil pressure switch...

your 87 might be equipped with 2 separate units for oil pressure...

here is a picture of the oil pressure sending unit.,.

http://contentinfo.autozone.com/znetcs/product-info/en/US/wl2/PS133/image/4/

here is the pressure switch for the fuel pump control..

http://contentinfo.autozone.com/znetcs/product-info/en/US/wl2/PS114/image/4/


this might also help...

the wiring diagram for the engine control system..

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/08/fd/99/large/0900c1528008fd99.gif



here is the diagram that shows the fuel pump wiring

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/08/fd/a1/large/0900c1528008fda1.gif



here is a chart with what the scan tool data should show on a good running car...

really explains what you should be seeing..

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/06/7e/6a/large/0900c15280067e6a.gif

i normally have people look at the scan tool data streams with the engine off and cold...

write the numbers down on one side of the chart... on the proper line...

then warm the motor... write the numbers down again on the other side  of the chart.. so you can sit and compare what is wrong...

makes it simple...  but bad solder joints... hard to diagnose... must examine.. to eliminate..  

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87L98Vette
I love my Chevy Chevette!
Posts: 14
Joined: 06/10
Posted: 06/21/10 04:43 AM

Wow...great info, I really appreciate this.
I am going to bypass the oil switch..drive it and see if the problem returns..then pull the ECM and go over the solder joints and finally upgrade the PROM. I will go ahead and swap the fuel pump and strainer as a maintainence precaution.

I'll let you know how it all turns out.  

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87L98Vette
I love my Chevy Chevette!
Posts: 14
Joined: 06/10
Posted: 06/21/10 03:29 PM

Well...drove it today and finally got it to turn on the check engine lamp and leave a code. I found a code 42 and the car stalled several times..I'm going to swap HEI modules and clear the codes and drive it again. I guess it could be and ECM as well..but I'll try the HEI module since I know those have a long history of being problems.  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 06/21/10 11:23 PM

Code 42
Electronic Spark Timing (EST) circuit grounded or Ignition Control (IC) circuit grounded or faulty bypass line


make sure that your spark plug wires are away from the 4 pin harness that comes out of the distributer...  

you might also have to check the electronic spark control module on the firewall... make sure the spark plug wires are away from it...

for all the other readers to come..

the spark plug wires create a magnetic field when the spark happens...

this can induce voltage in any wires nearby..

the wires leading to the spark control module have less than one volt AC on them...  some variable up to 5 volt DC...  start spiking them with dozens or hundreds of volts generated by being to close to the spark plug wires..  your timing is going to go crazy..

i would also advice.. to check the pick up coil for broken magnets in the stack...  just look... don't unscrew the 3 screws that hold it together. it takes a special tool to properly align it..  that nobody has...


the fast bird 93... web site shows optispark ignition diagnostics.. not HEI...


if you have time.. google code 42.... there were several articles spread around the web on testing this complex circuit...

i will try to find something tomorrow evening.....  

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87L98Vette
I love my Chevy Chevette!
Posts: 14
Joined: 06/10
Posted: 06/22/10 05:51 AM

I agree... I am going to replace the ESC module while I upgrade my PROM, and also replace all of the 25 year old components inside the distributor (inlcuding the capacitor and harness) . The igntion wires are high quality and routed properly...but that is an important tip to make since they can cause allot of strange issues. Hopefully have it all done by Friday and I'll post an update with the results.

Thanks for the help.....  

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wilsterzc4
V-6 Camaros rule!
Posts: 27
Joined: 04/10
Posted: 06/22/10 08:46 PM

wow u guys  talkin bout how easy it supposedly is to get to the fuel pump and on my 87 c4 l98 i opened the boot at the tank and see no pump...its internal ...according to my manual  

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wilsterzc4
V-6 Camaros rule!
Posts: 27
Joined: 04/10
Posted: 06/22/10 08:47 PM

and  by tha way is the ecm in the interior dash???cas i have searched and coclude thats where it is.  

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