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severe spark knocking during acceleration? help !!

Joined
Jul 4, 2007
Messages
19
Location
Viva Las Vegas
Corvette
1985 Silver & 1987 silver
Hello all and glad to be a new member. Just bought a 1985 z51 and it spark knocked pretty bad, got a EGR pintle out of position on my AutoXray 5000 scanner. The car has 76k on it and when I got it home changed plugs and noticed they were gapped at .045 instead of .035. put platinums in it and new MSD wires, new MSD blaster coil and ignition module along with new capacitor and harness. Checked pick up coil and was in spec. Added Shell Premium gas, a full tank and some DRY gas thinking water was in the tank. since 1999 car has been driven 2,140 miles. Also got Mobil one and a black mobil one filter, putting a fuel filter in and thinking about replacing the injectors while I have the plenum off doing the EGR and heater hose bypass of throttlebody.

WOULD A STINKIN EGR VALVE CAUSE THAT MUCH KNOCKIN? SOUNDS LIKE 8 BABY RATTLES IN THE BLOCK, REALLY BAD. ANYONE HAVE SOME INPUT, ALSO NOTICED HERE IN VEGAS TEMPS WERE AT 115 AND AFTER DRIVING TO STORE 10 MILES, CAME OUT AND CAR DIDN'T WANT TO START RIGHT AWAY, AFTER COUPLE CRANKS fine ???

has new air filter and all new vacume lines, rubber ones anyway didnt bother with the hard plastic ones, they looked fine. Sory about the babbleing, but there are some smart guys on this site, hope someone has had this problem in the past and can shed some light. Much appreciated ;shrug ;help :bash
 
Joined
Aug 30, 2002
Messages
1,533
Location
Colorado Springs, CO USA
Corvette
84 Z51 auto R.I.P. 89 black roadster SOLD
My first thought would be to check "base" timing with a timing light. Don't forget to disconnect the EST bypass (I'm guessing 85 has the EST bypass?)

Bill
 

motorman

Well-known member
Joined
Mar 7, 2002
Messages
849
Location
pa
Corvette
2008 Crystal Red Tint Coat
the EGR valve admits cooler exhaust gas into the combustion chamber to prevent spark knock(pinging). most all engines will ping when you remove the exhaust gas from the combustion process
 
Joined
Jul 4, 2007
Messages
19
Location
Viva Las Vegas
Corvette
1985 Silver & 1987 silver
thanks for the advice, will be changing this weekend, forgot to mention the timing was at 4 btc now at 6 btc, did disconnect the bypass. thanks will let everyone know the turnout..
 

Ruby Fan

Well-known member
Joined
Oct 7, 2004
Messages
189
Location
NY
Corvette
1985 Black Beauty Coupe, 93 Ruby, 96 CE vert
One other thing-put in premium gasoline, if you're not running that already. Timing could be off, maybe your dist. is loose and it turned a bit when you did the tune up.
 
M

mdsbch

Guest
I am very interested in what you find. I have an 85 coupe with the L98 and it runs great as long as you keep the RPM's under 3000. Once it exceeds 3000, it starts knocking like crazy. I've done all the tune up items as well as replacing wires, plugs, rotor & cap, tps, egr valve, even the ecm. I've been trying different things for over two years now and nothing has helped. So, now I just don't push it over 3000 RPM.
 
Joined
Jul 4, 2007
Messages
19
Location
Viva Las Vegas
Corvette
1985 Silver & 1987 silver
I am going to do the fuel pump today.. I only got a 30psi reading and it needs to be 36-40. when I turn key it bumps to 40 and then within 10 seconds falls to 15. my 87 same procedure turn key jumps to 43 and after 2 hours it is still at 33. on 85 they put a pulsation damper on the pump outlet inline with fuel line, its sloppy connection you just push pump and line into a rubber grommet, no clamps? everyone complains that it loses pressure over time, you still get fuel just not enough...

my 87 has the pulsation damper next to fuel filter on frame rail ??? looks like there was an issue to redesign after 2 years, maybe 86 they changed, I have 85 and 87, different.

check you fuel pressure, you can get guage cheap, do it on the schrader calve in passenger side, see you pressure reading, that will tell..

once I fix it later or on sat, will update thread to see if spark knock gone.....

by the way always use premium, even tried 103 octane racing fuel, still did it..

thanks
 

David-F

Well-known member
Joined
Mar 28, 2007
Messages
53
Location
Woodstock,GA
Let's get a few things stated at first if you have the original injectors in the car the fuel presure at idle should be about 28 to 32psi it's only if it has been updated to the later injectors which needed 36 to 40 psi at idle this has to do with some of the things done to help keep the injectors from clogging up so easy. Also something you realy need to do is get a scan tool on the car you need to check block learn and intagrator and see if they are around 128 if they are way off you may have a problem with the MAF sensor it is not that uncommon that over time the MAF sensors shift and when they do it can lean the engine out and make it ping. Now the car does have a knock sensor and it needs to be checked in most cases the knock sensor will cover for the EGR not working in which you might get a slight ping at first but stop real quick. But Ping under heavy acceleration has nothing to do with EGR. Egr only operates under light load on warm engine. To test the Knock sensor you will need a timing light a long rod and a hammer, just warm the engine up bring the idle up to 2,000rpms with the timing light watch the timing while someone else takes the long rod and places it on one of the head blots then hit the rod with the hammer the ECM should remove timing and you should see if with the timing light. Also the pre campaion cars whould have called for a .045 spark plug gap but the new ign. module used ledd coil seration so it needed a smaller gap.

David Fulcher
 

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