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pretty sure my ecu is bad, double check my diag?

presterone

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Jan 23, 2012
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brunswick maine
So started with a rough running and stalling issue. Code for air meter, vehicle sat for a few months, changed MAF and then car wouldn't start or sputter at all. Checked for spark, had spark but a dead fuel pump. Replaced pump, it powers up just fine and still no start. Checked for spark, no spark. No power at the injectors. MPI relay is good and has power to one leg with fuse removed. Swapped main efi relay(big bronze) double relay and still no start. I have power at one pin of the main relay and two with ignition on.
 

presterone

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Also no CEL lights up when key is on and supposedly its had the caps replaced less than two years ago
 

slugsgomoo

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open the case, inspect for any scorch marks, and sniff for smells... also, might take pics of the inside of the ecu and let us have a gander.
 

presterone

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Pulled the cover off and there is a residue around the caps and the large "chip" looking thing near the caps has black residue around the pins. What makes me second guess all this, is if the residue is from a poor solder Job or the old caps leaking? No odor either. They are relitavely new but still can fail I imagine.
 

presterone

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OK so I got a non eprom ecu from a 91 gvr4, the car runs but doesn't want to idle and sputters a bit on lower rpm. Are there any pins I need to swap?I could only find info comparing 1991 cars to 90. Also my boost gauge is doing some weird stuff(factory cluster boost)
 

presterone

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I will get the nu!mbers tonight, what I mean by weird stuff is when I'm keeping the rpms steady at 2k with the car standing still the boost gauge will fluctuate.
 

presterone

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So it's weird my check engine light still doesn't come on with the key on. The car runs and drives but won't idle. The 91 gvr4 ecu part # is md165810 with an e suffix at the bottom. The ecu has rebuilt stickers from ZDR electronics.
 

presterone

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According to vfaq the 91-91 gvr4 part numbers are the same. So no swapping pins tomorrow I'll check for battery voltage at the ecu and grounds. I wonder if a shorted wire has just enough voltage to run the car but not have the ecu working 100% thus not allowing the CEL to come on. Just a hunch I hope that's all it is.
 

slugsgomoo

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Technically the eprom in the 1g & vr4 are slightly different because the vr4 came with a "hacked maf" from the factory, though I doubt it would cause this.

How modded is the car? (specifically anything fuel or turbo/piping related). Have you done a boost leak test? Have you attempted to set the BISS screw properly?

Stock ecu estimates boost based on airflow and that makes me suspect weird airflow readings causing the fluctuation there.
 

presterone

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brunswick maine
Both cars are 100% bone stock and this not a 1g ecu. Before I start looking into other things I want to know how the CEL still doesn't come on with the key on. but it does run and cruises, it just doesn't idle.
 

AllanL

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Aug 4, 2008
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NV
CEL might be something blown int he ECU.

had this same problem when i shorted the wire to the CEL light on the dash.

poor idle may mean some problem in the ISC drivers or the circuit from the pin out to the driver.

also had this issue, when the pcb trace on the ecu was cut and half of the isc circuit was not giving any signal to the isc.

here's a link:
click
 
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