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Engine stalls under alternator load
Topic Started: Aug 7 2012, 08:26 PM (1,426 Views)
kyle presley
New Member
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Hello everyone!! I am a new Geo Metro owner. This forum is great! I have learned so much lurking here, but it's time for me to post something of substance. I am having one nagging problem on an otherwise great little car. I hope y'all can help me.

OK, so I bought a 1993 Geo Metro XFI about two months ago. It had 400k+ miles on it, but the interior and exterior were very cleans and the engine had been remanufactured by Jasper and had 63k miles on the rebuild. It lacked power and the engine would go to a very low idle nearly stalling under a full alternator load (headlights, blower, fan, turnsignals, brakelights, etc), basically whatever I could turn on.

I immediately suspected after some research that I had a bum IAC valve. So, I took it off, opened it up. The leaf spring was completely intact, so I cleaned the crud off of the leaf spring and the hole inside the IAC, put it back together, then reinstalled it in the Geo. It did not fix the problem. Still nearly stalled out under a load.

Me and a mechanic friend of mine did a compression test: 65, 135, 125. We noticed that there was coolant coming out the tailpipe, and oil leaking from the head gasket on #1 cylinder. Decided to do a rebuild. When we pulled the head, the gasket was blown around #1 cylinder. We discovered also that the pistons were maxed out oversized at 0.040 (1mm) over.

We:
took the head to a machine shop, two of the exhaust valve ports were out of round and the guides were enlarged. So all valves were re-seated and replaced the two exhaust valves. Left one of them alone because it was within specifications, but all vlaves were taken out inspected, re-seated and everything was cleaned up and put back together as it should be.

Changed the pistons and rings, changed the main and rod bearings (checked the journals on the crank to make sure we got the right bearings). Had the machine shop polish the journals on the crank, and put in the two thrust washers. I also changed the fuel filter.

One thing that I meant to do was to clean out the EGR system, but did not. That, and the throttle body did not really get overhauled. i cleaned the surface grime off with Carb cleaner and a few of the ports, but nothing serious.

Now, everything is put back together. fiddled with the idle air screw, set, reset, and rechecked the TPS by my Haynes manual. I still have the darned idle problem...

I have checked and rechecked the timing gears and belt, completely in time. And checked and rechecked my spark timing. Once I stabilized the idle properly (somebody jiggered with the factory set screw before I bought it, as the cover was missing and the timing was advanced to 20 degrees!!!!), I was able to get it to run right and set base timing to 8 degrees.

So I took the IAC valve back off, cut off the leaf spring and did the inkpen spring modification described in thread on here. No change. I ordered a new to me IAC off a 92 Metro from eBay. installed it. No change. reset the ECM by pulling the positive terminal off the battery (for the 3rd time) and wa la! The thing started actuating when I put the car under a load. BUT it barely compensates the idle at all.

My temporary solution was to idle it up via the air screw, and get some assistance from the IAC. I can tell that there is some vacuum coming through the port in the air cleaner where the IAC vacuum hose connects when I put the car under a load, and there is no vacuum when there is no load. And I can hear the IAC actuating.

I took it apart and the leaf spring in the new-to-me IAC valve and it was completely intact, so I just cleaned the crud off with a shop towel and put it back together and stuck it back in the car. No change. I can hear it working, and feel a little vacuum against my thumb under a load, but it's not doing much to the idle.

Me and my mechanic friend who helped me do a rebuild helped me check my fuel pressure. We pulled the main fuel line going to the throttle body and plugged into a fuel pressure gauge, and it maxed out the gauge with one prime of the fuel pump by turning on the switch. The gauge only goes up to ten pounds (for small engines maybe?), but it maxed it out pretty quick. I feel safe ruling out fuel pressure.

I checked my alternator, fluctuating voltage between 13-14 volts under a load, but with the engine idled up a bit so it wouldn't die, so maybe a false positive...

I Have ruled out the TPS... Everything checks out as it should (at least as far as resistance is concerned), which is all the book says about testing it.

So what am I doing wrong? Could my alternator be bad? Do I need to buy a brand new IAC ($85 from autozone)? Clean the EGR system? Thoroughly check my fuel pressure? Am I missing something? Any and all help would be very much appreciated.Thank you!

:banghead :banghead :banghead :banghead :banghead :banghead :banghead :banghead :banghead :banghead :banghead


P.S. I live in the Deep South, lots of junkyards around, but none with a single Geo Metro of any sort in it... I guess Metros don't have enough power for them to be popular here (rednecks like their power!).
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Memphis metro


Have you verified all vaccum lines are routed correctly and checked the grounds on the back of the intake? You might want to also check the catalytic converter for a partial restriction.
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kyle presley
New Member
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As far as I can tell, all vac lines are routed correctly. I replaced a lot of them, on the rebuild. I have not checked the cat, is there a thread on the procedure?
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kyle presley
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kyle presley
Aug 7 2012, 08:54 PM
As far as I can tell, all vac lines are routed correctly. I replaced a lot of them, on the rebuild. I have not checked the cat, is there a thread on the procedure?

I do believe that everything is grounded also. No wires are hanging loose. All plugs are plugged, no vacuum leaks.
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DesmondGhostRider
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to check the cat unplug the o2sensor and see if she runs better. :) Your belt might be on too tight...
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Memphis metro


The best method of checking for restricted converters is to tap into the vaccum line at the map sensor with a vaccum gauge and check your vaccum.

Check out post 81 here,

http://geometroforum.com/topic/4464045/6/.

You could undo the exhaust from the manifold and run it and see if you notice more power. It will be loud though. Is the check engine light on by chance?
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kyle presley
New Member
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No check engine light. When I unplug the electrical plug to the map sensor, the car dies, but I have not checked the vacuum to it yet. Exhaust is strong and hot out the tail pipe.
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kyle presley
New Member
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I unplugged the MAP vacuum line from the rear of the throttle body on the TPS side, and there is a significant amount of vacuum from the throttle body. I don't really have a way to test it t'd into the MAP, but it doesn't act up when I rev the engine. It does seem to drag a bit going up slight inclines, can't usually get it over 50 MPH when going up a slight grade... It idled up when I unplugged the hose, idled down when I plugged the port on the TB with my thumb, and was stable when I reconnected the hose.

Edited by kyle presley, Aug 8 2012, 12:15 AM.
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kyle presley
New Member
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I unplugged the oxygen sensor (that's the plug on the passenger side of the exhaust manifold right?) and RPMs dropped by about 10-20 RPMs, and further still under a load.
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mwebb
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FOG

suspect bad ground on alternator / engine to battery negative

connect your DVOM to MAP sensor ground
use T pins
see T pins in electrical area

there are 3 pins on the MAP sensor , one is ground , check all three , engine at idle to find which one

with engine running
from MAP ground to battery negative , voltage must be 50mv or less

then
turn on hi beams and heater blower to speed 4
does the MAP ground value change ?

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kyle presley
New Member
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Thanks MWebb, I will check that tomorrow in the daylight. This evening me and my buddy did a compression test on our newly built engine: 175, 175, 125... We got problems somewhere. I am thinking the head, because we did extensive head work... IDK. I think that may be the problem, or at least a contributing factor.
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mwebb
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FOG

kyle presley
Aug 8 2012, 09:31 PM
Thanks MWebb, I will check that tomorrow in the daylight. This evening me and my buddy did a compression test on our newly built engine: 175, 175, 125... We got problems somewhere. I am thinking the head, because we did extensive head work... IDK. I think that may be the problem, or at least a contributing factor.
then connect your vacuum gauge Teed into the vacuum line to the MAP sensor
before the restriction orifice
should be 20" at hot idle , steady , no flutter in the needle

if there is any flutter or if vacuum is much below 20"
yes
there is a mechanical fault .
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