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Detonation - need help
Topic Started: Jun 7 2010, 11:29 PM (1,726 Views)
92GoCart
New Member
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I'm having detonation problems that I can seem to get ironed out. It pings only after the engine is fully hot in 70+ degree weather (hotter more ping of course). It's the worst under load on a good grade but will also do it if accelerating hard on the flat. Cruising under light to moderate throttle on the flat is okay. The car is a '92 1.0 base model. It was given to me with a broken piston a couple years or so ago. While fixing it I pulled all the pistons out and cleaned everything up real well and checked tolerances. Everything was well within service limits and looked good so I put it back together (was trying not to put too much money into it). Dry compression is 175, 177,180 on a hot engine at WOT without removing all plugs. I removed and cleaned the EGR system although the head passage may not be 100% I don't know but it will die if I open the valve and exhaust did come out when I started it with the valve off. I verified that the mark was correct by removing #1 plug and rotating back and forth with a screw driver in the cylinder. I haven't verified the cam timing but I'm 99.9% sure it's good as I have done piles of timing belts over the years. I also marked the dist. before opening things up and with it set at my mark it times out to very near 5º. I tried 91 octane fuel and this may have helped a tiny bit but not much. The engine should be clean since I have put only about 1k miles on it since it was apart. I sea foamed it anyway and so far this hasn't done much if anything. I have it in the fuel right now and I drowned it tonight and then took a ride running 65-70 for about 18-20 miles. I tried it as low as 3º and still had some pinging. Of course this cuts the power so this can't be the answer. I put new NGK G-power plugs in. It had Autolites before this that were in good shape and not dirty. Cap, rotor and wires look great. I cleaned the cap electrodes. I haven't done a lot of fuel experimenting because I don't put on a lot of miles. Work is .9 miles and town is 4 miles. Anyway it's really a pain because I have a good grade coming out of town and I have to run 4th gear and keep loosing speed most of the time just to get up the hill without a lot of pinging. I can't run the A/C much either unless going down hill or maybe on the flat with no wind. Has anyone ever run into a bad ECM causing this? It is adjust the timing because it will retard when the terminal is shorted for timing. I removed all the grounds I could find in the engine bay and sanded under them. I also got one inside on the passenger side.

I don't know if this is related or not but I'm also having trouble with the IAC as well as the A/C air valve. I have posted about the IAC before but it never has been resolved. What happens is that when the throttle is cracked open and then closed again the IAC will kick in strong and idle it way up. It will then come back down to normal in under 30 seconds. While it's letting all this air in the exhaust sounds rough, kinda like when the timing is really far advanced and you get a sort of missing puffing sort of sound out the pipe. I did install a new valve as it had a broken part inside but this didn't help.

Okay now for the A/C air valve. This thing isn't opening up enough so the idle is quite low and the engine really shakes. The valve has a good 12 volts and snaps fully open when jump from the battery. I took it apart and it all looks good. I played with the air adjuster screw some. If I tap the solenoid with a wrench while the A/C is on it will open up a lot more. What I wonder is if the ECM isn't grounding the thing good enough. These three problems keep making me wonder about the ECM.

I also checked for codes but there were none other than the all is well code 12. I think I covered everything I have done so far. It's a good clean little car and I'm getting 46-47+ consistently so I sure hope I can fix this stuff. I don't have an OBD1 scan tool so this limits me some.

Anymore ideas I can try? I almost to the point of finding a used ECM just to see but maybe that's going too far. I just don't know how to determine if one is bad or not.

Mark
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starscream5000
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Got 70 MPG?

I've been off a tooth before after setting timing, but that was with a modified stock camshaft gear. Have you verified that crankshaft to camshaft timing is set correctly and not advanced by one tooth? It will still run, but ping easier. Ask me how I know ;)
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mwebb
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FOG

voltage drop testing on the ground on the back of the intake
must not be more than 50mv different from battery negative

T in a vacuum gauge to EGR diaphragm , with long enough vaccum hose that you can put vacuum gauge in the car or under a wiper where you can view it , drive car
at cruise , or very light acceleration
should be around 5" vacuum at EGR diaphragm

intake vacuum at hot idle
with vacuum gauges Teed into MAP sensor line before MAP sensor orifice
MUST be about 20" and zero flutter
IF the value is low , valve timing is INcorrect - (timing belt marks are not lined up properly)
crankshaft wheel can slip .... marks may be lined up but not lined up ,intake vacuum will tell the tale
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Bad Bent
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Facetious Educated Donkey

Good posting, starscream5000

I was very sure I had my cam timing set correctly but was still a tooth off. The belt should not be stretched or the tensioner loose or having a bearing problem. :hmm

Just curious but the plugs are the correct heat range and gapped to the hood sticker .039-.042 or what ever. But you said the Autolites were clean.
Have you considered replacing all your vacuum hoses? :dunno
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crankcase


If all else fails, check the compression. If one cylinder is low that could indicate a possibility for investigation.
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rmcelwee
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I'm not sure how forgiving the Metro temp gauge is but your car might be over heating (just guessing here). Remove the thermostat and see if your problems go away. Again, just a guess but it is easy enough to try.
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92GoCart
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Thanks for the ideas guys. I will put in more time on this when I get a chance and make 100% sure the cam is in the right spot.
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92GoCart
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The highest I got the EGR vacuum was 4" although the gauge may have been reading low (compared to another one I used and compared too on intake vacuum). I fully removed belt and checked everything and just as I thought everything lined up perfectly. Crank woodruff key was fine, sprocket marks were lined up as well as the cover timing mark. I have bad intake flutter. Depending on idle speed, which varies some, it flutters between 14" and 18". Since the cam appears to be in time my guess would be one or more intake valves leaking? Or could it be lifters pumping up too much? I am running 5w30 dino oil. I lapped the valves good when I put it together about 1k miles ago so I don't see why they would be leaking. A dry compression test from some time back was 175,177 and 180 hot. I didn't remove all the plugs while testing. There is slight valve train noise but its seems minimal to me. I don't know what is normal on these engines.

How do I test for voltage drop between intake ground and battery ground?
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doug7x
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This may be a little obvious, but did you actually check the IGNITION timing?....If it's too far advanced (more than 12 or so BTDC), it will do exactly as you describe. Good luck
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crankcase


What is the voltage between the intake ground and battery neg ?
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92GoCart
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crankcase
Jun 10 2010, 09:28 PM
What is the voltage between the intake ground and battery neg ?
I'm not sure how to measure that, please explain.

doug7x: yes the timing has been checked multiple times. I have had it as low as 3º, which helped a little.
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crankcase


Put the multimeter on DC voltage.
Put the neg lead of the meter on the neg post of the battery.
Put the pos lead of the meter on the intake ground.

See what the reading is.

The battery ground and the intake ground should be at the same potential.
Another way to say this is that they should both be like a single piece of metal.
Hooking something up to the battery should be like hooking something up to the intake ground,
(just like they are the same piece of metal).

There should be 0 volts between them if you try to measure the voltage difference (as shown above).
If there is a poor connection because of rust, a loose bolt, or corrosion etc,
the two "grounds" will not be like they are both parts of the same piece of metal.
This is the type condition you want to be shure you don't have!

This will be shown in a voltage test as described above.
If it is not too extreme, there may be a small voltage drop like .25 volts,
but even this small value is no good.
Anything more/higher than around .05 (50 millivolts) is not too good.

In an extreme case you will read an open circuit. This means there is
no connection! An open circuit = very very very very ....... large voltage drop.

You should see a reading of less than .05 or 50 milivolts if all is well, but
make shure your test leads are making FIRM contact with the metals.

Sorry for all the wind, hope it helps.

P.S. I can't remember where I got the 50 milivolts figure,
I think mwebb mentioned it?? It's sounds like a good figure.
Edited by crankcase, Jun 10 2010, 10:19 PM.
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mwebb
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FOG

...."The highest I got the EGR vacuum was 4"
although the gauge may have been reading low (compared to another one I used and compared too on intake vacuum). I fully removed belt and checked everything and just as I thought everything lined up perfectly. Crank woodruff key was fine, sprocket marks were lined up as well as the cover timing mark. I have bad intake flutter. Depending on idle speed, which varies some,

it flutters between 14" and 18".

Since the cam appears to be in time my guess would be one or more intake valves leaking? "....


yes
you have a problem - since compression was "good" i would do a leak down test next
because 4 " of flutter indicates a valve sealing problem

since your intake vacuum is too low as well ...

assuming the EGR is not stuck open
assuming the EVAP PURGE valve is not pulsing in time to the flutter

intake vacuum at hot idle should be 20" and steady smooth with zero flutter
22" at 2k rpm with EGR disconnected
20" at 2k rpm with EGR connected
0" @ WOT snap followed by 24" as engine decels to idle

IF these values are all TOO LOW , suspect CAM TIMING OR restricted exhaust
=============================================
when you get that sorted out
switch to synthetic oil
European Specification ACEA A3 B3 - B4 5w30
since oil change interval jumps to 6k miles it is cheaper to use , and so much better
mobil one 0w40
german castrol 0w 30
OEM :
BMW LL01
VW Audi 504
MB 229.5
any of those will do , cheapest will be BMW LL01 from a BMW dealer , at least in my area .

in use Mobil one 0w40 tests as 5w30 as per Blackstone Labs.

Mobil One 5w30 is not good enough and does NOT meet the ACEA A3 B3 - B4 specification
MOBIL One ACP 5w30 may be , but i have NEVER seen it for sale anywhere
see " BITOG "forums
Edited by mwebb, Jun 10 2010, 11:21 PM.
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92GoCart
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Does the key need to be on for this or the engine running? Seems like there would have to be some current flowing some place to be able to get a reading of voltage if there was a bad connection. Some weeks back I did remove and clean all the grounds I could find. I will try this test in the morning.
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mwebb
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FOG

92GoCart
Jun 10 2010, 11:15 PM
Does the key need to be on for this or the engine running? Seems like there would have to be some current flowing some place to be able to get a reading of voltage if there was a bad connection. Some weeks back I did remove and clean all the grounds I could find. I will try this test in the morning.
engine running
Hi beams on
heater blower on MAX
rear defogger grid ON
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