C4 Demons
Thread Starter
Cruising
Joined: Feb 2014
Posts: 12
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From: Newport NC
C4 Demons
upOk folks,my 88 has gremlins,lol..here's my issue,my ole' girl just falls flat on her face at3500 rpms..i did the code check using the paperclip method,( being as no local shop has a tech 1) codes came back knock sensor(I replaced) MAS (so far ive replaced just the relay).id like to get a better reading before I spring for the MAS as they aint cheap..also what if? any ideas? Ill gladly replace the MAS if I can be sure that's the problem..id love to drive my vette again..thanks madbiker..
PS id like to approach this without jus doing the shade tree thing and jus start throwing parts at this problem..as we all know that can get expensive..PLEASE HELP!! LOL
PS id like to approach this without jus doing the shade tree thing and jus start throwing parts at this problem..as we all know that can get expensive..PLEASE HELP!! LOL
Last edited by madbiker; Oct 22, 2015 at 03:49 PM. Reason: more input
Team Owner
Joined: Dec 1999
Posts: 34,873
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From: Lacey WA RVN 68-69
NCM Sinkhole Donor
Will the engine rev beyond that RPM with the trans in neutral or just under load like when driving?
I would check fuel pressure; you can get a fuel pressure tester to rent and connect it to the Schrader valve at the fuel rail then tape it to the windshield where you can see it or take a passenger along. Look for any big changes in the psi reading.
You may have a clogged fuel sock which is attached to the fuel pump assembly. Can't hurt to replace the fuel filter.
Also remove the distributor cap and check the condition of the brass terminals and also the rotor. Is there any sign of excessive corrosion? How old are the plug wires and spark plugs? Old wires can have a lot of resistance which will reduce the voltage at the plugs. If the plugs look fouled from running too rich or from burning oil, it could be difficult for any of them to have a good spark at the electrode.
You can alsoremove the MAF sensor and clean it with some MAF sensor cleaner. CRC makes a good cleaner and you can find it at any parts store. Simply spray the MAF and let it dry, then re-install.
I would check fuel pressure; you can get a fuel pressure tester to rent and connect it to the Schrader valve at the fuel rail then tape it to the windshield where you can see it or take a passenger along. Look for any big changes in the psi reading.
You may have a clogged fuel sock which is attached to the fuel pump assembly. Can't hurt to replace the fuel filter.
Also remove the distributor cap and check the condition of the brass terminals and also the rotor. Is there any sign of excessive corrosion? How old are the plug wires and spark plugs? Old wires can have a lot of resistance which will reduce the voltage at the plugs. If the plugs look fouled from running too rich or from burning oil, it could be difficult for any of them to have a good spark at the electrode.
You can alsoremove the MAF sensor and clean it with some MAF sensor cleaner. CRC makes a good cleaner and you can find it at any parts store. Simply spray the MAF and let it dry, then re-install.
Race Director
Joined: Oct 2008
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From: Lansing MI
" flat on its face " is hard to understand. I've heard those exact words used to describe everything from a misfire to a slipping transmission.
To me language like that means a lean condition which woukd make sense with your mass air code. Just to see, I woukd disconnect the Mas electrical connector just to force the ecm to run in open loop and see what happens. If there isn't really any status change with the symptoms then I would keep looking with an eye toward the fuel system.
To me language like that means a lean condition which woukd make sense with your mass air code. Just to see, I woukd disconnect the Mas electrical connector just to force the ecm to run in open loop and see what happens. If there isn't really any status change with the symptoms then I would keep looking with an eye toward the fuel system.
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From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
QUOTE c4cruiser
check fuel pressure
replace the fuel filter.
clogged fuel sock which is attached to the fuel pump assembly
Very common for C4's with your symptoms. Do these first!
check fuel pressure
replace the fuel filter.
clogged fuel sock which is attached to the fuel pump assembly
Very common for C4's with your symptoms. Do these first!
Thread Starter
Cruising
Joined: Feb 2014
Posts: 12
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From: Newport NC
thanks will do,lol sometimes I have a senior moment and forget about basic maintaince issues like O2s
Thread Starter
Cruising
Joined: Feb 2014
Posts: 12
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From: Newport NC
C4 gremilns
[
lol, sorry for the terms but that's what it seems like. when I start the cat cold the engine will tach to about 4k..but not for long..when hot,about 2500 to 3500 rpms is about it. the engine dose not die. really does seem like it not getting fuel,or possibly a timing issue..Im going to start today rule out simple ignition issues..then work my way to the cats n last MAS..the car does smell like its running rich tho..thanks for yours n all input..Gary
" flat on its face " is hard to understand. I've heard those exact words used to describe everything from a misfire to a slipping transmission.
To me language like that means a lean condition which woukd make sense with your mass air code. Just to see, I woukd disconnect the Mas electrical connector just to force the ecm to run thank for the input..Garyin open loop and see what happens. If there isn't really any status change with the symptoms then I would keep looking with an eye toward the fuel system.
To me language like that means a lean condition which woukd make sense with your mass air code. Just to see, I woukd disconnect the Mas electrical connector just to force the ecm to run thank for the input..Garyin open loop and see what happens. If there isn't really any status change with the symptoms then I would keep looking with an eye toward the fuel system.
lol, sorry for the terms but that's what it seems like. when I start the cat cold the engine will tach to about 4k..but not for long..when hot,about 2500 to 3500 rpms is about it. the engine dose not die. really does seem like it not getting fuel,or possibly a timing issue..Im going to start today rule out simple ignition issues..then work my way to the cats n last MAS..the car does smell like its running rich tho..thanks for yours n all input..Gary
Last edited by madbiker; Oct 24, 2015 at 04:11 PM. Reason: typo's
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From: Kingman AZ
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St. Jude Donor '06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16
The logical way to fix this is to diagnose the problem with the help of a flow chart from the factory service manual. You can usually find one on eBay - either the set of 2 books or the CD
Pro
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From: Allentown Pa
Thread Starter
Cruising
Joined: Feb 2014
Posts: 12
Likes: 0
From: Newport NC
C4 gremilns
Thread Starter
Cruising
Joined: Feb 2014
Posts: 12
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From: Newport NC
C4 gremilns
why 3 cats,lol if I replace I woild use 2 cats, an x pipe ..true duels out the rear..any input? thanks Gary
Team Owner
Joined: Dec 1999
Posts: 34,873
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From: Lacey WA RVN 68-69
NCM Sinkhole Donor
The main cat could be breaking apart inside and keeping the exhaust gasses from flowing freely. You will have to remove it to check.
A true dual exhaust would be a good mod, especially if you go with headers. An X-pipe can be placed in the location where the main cat sits. There's a pipe leading to the main cat from the AIR pump; just secure it so it doesn't bounce around and rattle. Make sure you leave the existing O2 sensor in place. I installed headers and true duals on my '87 and I welded a bung in the left side header collector for the O2 sensor and it works fine in that location.
Thread Starter
Cruising
Joined: Feb 2014
Posts: 12
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From: Newport NC
C4 gremilns
Are you required to have the car smog tested? Is there a visual inspection? If no visual, you can replace the front Y-pipe and the two pre-cats with a Y-pipe that doesn't have the pre-cats. The accessory catalogs will have them. Otherwise cut the pre-cats out and weld in some pipe.
The main cat could be breaking apart inside and keeping the exhaust gasses from flowing freely. You will have to remove it to check.
A true dual exhaust would be a good mod, especially if you go with headers. An X-pipe can be placed in the location where the main cat sits. There's a pipe leading to the main cat from the AIR pump; just secure it so it doesn't bounce around and rattle. Make sure you leave the existing O2 sensor in place. I installed headers and true duals on my '87 and I welded a bung in the left side header collector for the O2 sensor and it works fine in that location.
The main cat could be breaking apart inside and keeping the exhaust gasses from flowing freely. You will have to remove it to check.
A true dual exhaust would be a good mod, especially if you go with headers. An X-pipe can be placed in the location where the main cat sits. There's a pipe leading to the main cat from the AIR pump; just secure it so it doesn't bounce around and rattle. Make sure you leave the existing O2 sensor in place. I installed headers and true duals on my '87 and I welded a bung in the left side header collector for the O2 sensor and it works fine in that location.
Thread Starter
Cruising
Joined: Feb 2014
Posts: 12
Likes: 0
From: Newport NC
C4 gremilns
during my testing she started blowing rust chips out of the exhaust,hmmm could be clogged huh..glad I planned to redo the exhaust anyway..hope this is problem solved
Thread Starter
Cruising
Joined: Feb 2014
Posts: 12
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From: Newport NC
C4 gremilns
well through all this revving n playing with this ole girl,,she started blowing rust chips out the exhaust, some as big as a dime..if this is indeed my problem.i already planned to rework the exhaust..suggestions? I'm
not into some fancy SS kit..or even a kit at all.what id like is good flow, nice growl..lol thoughts?
many thanks to all for the input Gary
not into some fancy SS kit..or even a kit at all.what id like is good flow, nice growl..lol thoughts?
many thanks to all for the input Gary