Losing half of the power..like an open ground

[DSM1G90]

Need a little help here:

My Laser is beginning to experience an unusual condition, which is losing half of the power output from the motor.

Let me begin: After sitting for a few days, I start the vehicle up and it fires up smoothly and with an idle of 1400rpm with no CEL light and vehicle is warming up normally.

About half way to full warm and just on idle, in which the FIAV is doing its thing when coolant is warming up causing idle speed to reduce, the system suddenly goes in to half power.

Meaning that suddenly, the motor just either runs on two cylinders, or two injectors are losing time. The readings from the tach suddenly is reading half of the motor's RPM output at idle. For example, if the motor is spinning at 1000 rpm, the reading on the tach is at 500.

I recently did an injector changeout since one injector went bad using stock 1G 450s to match the ECU (MD128625) setup.

I also have a CEL with many codes stored. Barometric, Temp Sensor, MAF for beginners.

I did pull plugs and all were clean and firing normally for I was waiting to find two of them soaked with fuel, or soot black due to weak ignition, bad plug wires and/or broken connection within the plug itself.

I did replace the ignition coil and temp sensor this summer since I had a hard start problem where I heard that I was fighting injector fuel timing and a replacement of the temp sensor cured that issue hands down along with allowing more performance to come from the motor.

I did, after disconnecting the negative from the battery, pulled the connectors and reseated the connectors on the ECU to ensure both that the connecting pins were fully seated in its respective connector and a solid contact was made to the connection to the ECU. It is this is when I first started the motor up and it fired immediately into the warmup idle, ran smooth for a good while until it went into its version of a "limp mode" of running in half power.

To me, it sounds like a ground opening up causing my issues. But, one would thing that an open ground would stay open instead of closing to make connection, or is there something more complex...like could I have a bad CAS or similar and how to test if so.

Thx for all help with this issue, for I've covered all the bases I've been thinking of.

-DSM

 

[91-GS]

Have you tried unplugging the idle control solenoid (and letting engine warm up that way) to see if it's at fault?

 

[DSM1G90]

No, for the condition actually began while tooling on the freeway doing 75mph - a sudden loss of half the power, CEL light coming on, tach reading half of its value and boost gauge showing slight boost during the loss.

I managed to nurse the thing home running on half power and just let it sit for a few days before I began the areas of condemnation with first pulling plugs to check their condition, checking injector connections to reseating the ECU connections. After all of these said checks is when I fired the unit up where it started normally until it got half way hot is when it began the loss of power situation.

Thx for the tip anyway. Something to check into - DSM

 

[91-GS]

Doesn't hurt to check, even if it's most likely not the cause.
Did you hit any bump or a hole right before the problem? Thinking it might be as simple as a bad connection on the battery, seeing how everything is acting up at once.

 

[DSM1G90]

Fully agree as a possible and simple thing as a bad battery ground or similar .. and more to check out.

Love how you did a gull wing conversion on your 1G, by the way .. quite unique in as well great looking.

Good luck and thx - DSM

 

[91-GS]

Had a problem with a car where it was acting up as if the battery was going dead at random. Checked it with a volt meter and got a good reading. Yet it kept loosing power to everything electrical. Even checked all connections and everything was tight. Turned out to be a bad connection between negative battery terminal and the large ground wire off that terminal. Turns out that the best way to test for a bad connection like that is to measure the battery first and then measure between a positive post of battery to ground (for bad ground), or from negative of battery to positive wire (for bad positive). Do crank the car over while measuring. Doing so will put enough power draw on the system and make it much easier to spot the "bottleneck" (i.e. a bad connection) by observing voltage changes VS the voltage of battery itself.

If you want to discuss the doors, here is a thread that would work a little better for discussing it. Glad you like them, but let's keep this thread about YOUR car

 

[DSM1G90]

UPDATE: Checked all grounds and tightened if necessary, attempted to fire the thing over in which took a few tries but did manage to catch, but still on two cylinders. Let it run like that for a bit then turned if off.

Did a CEL code reading since the light came on shortly: 4 long and 4 short pulses. Code 44.

Now pointing to a coil issue (in which I did replace the coil this summer), and/or Power Transistor (which would be the original installed one).

Maybe this was a growing situation when I changed out the coil when on side's resistance was off the scale on the old coil causing it to affect the transistor and finally has let go... more to check on now.

DSM

 

[91-GS]

A simple way to check the coil is to swap them both. Now the "suspect" coil runs other two cylinders and if the problem is in fact the coil, it will be obvious since the problem will not be with cylinders it was before.

Edit: Here is a thread discussing ignition system. Post 6 mentions a power transistor, and how if it goes bad (or one of the connections gets corroded) that car will start missfiring.

 

[DSM1G90]

Thx, been watching this post and wondering if it is the transistor. Now, I do have Chilton's manual but this book sometimes doesn't contain all needed info.

With my '90, I have the five pin power transistor,whereas the Chiltons only has illustrations from '91 and up with these units having more pins in the connectors. Thus, where would one find a visual on how to do this test for the five pin transistor module?

thx - DSM

 

[curt-s]

You check every inch of wiring in the harness?

That's what I have to do I get random cut-outs and cruise bucking, and frequent suddenly-dead O2 readings at idle. Happens off and on. Found lots of problems in the wiring, even underneath factory tape, but I think I've got to go all the way to the ECU. Maybe even a new harness. Just a heads up, your components (though aged) may be fine still..

 

[91-GS]

Is this what you are looking for?

 

[DSM1G90]

Yes..thx much for the visual info to where I can use and save this for future info. - DSM

 

[91-GS]

Got entire tech manual for a 1990 DSM so lemme know if you need anything else out of it.

 

[DSM1G90]

OUCH ! Found my issue using luv2rallye's tip in that one post using the battery - a 1.5 and 12v (in which I used a 12v garage door opener battery and an 12v mini dash indicator light):

One side of the module , "OC1" opened up (no light when I touch the 2nd pin with the 1.5v battery) and the other side "OC2" has dead sorted across (with 12v across ground and pin 6 and light came on).

With this one that has dead shorted across, I bet I also toasted the one coil (1/4) since it was getting 12v primary voltage all the time since it wasn't switching on and off and kept the primary winding on all the time

...like an old points system distributor: feeler gap never opened to collapse the primary winding in the coil.

Found some modules on the Rockauto site. Now, which one to choose ...

Thx for the help - DSM

 

[DSM1G90]

UPDATE: With other users having the classic "1-4" not firing and with coil and transistor replacements, it really makes one wonder what is going on for the system not to get back in a closed loop condition.

I did the replacements of both units and go my vehicle back in running order along with gaining some extra power that was hidden due to tired electronics.

Yet, wish to say "Thank you" for all that helped me with tips, suggestions and printed layouts to guide me in this quest for a running vehicle again. Those who helped, please keeping offering all the help to the ones who comes on this site to get their vehicles back on the road again.

Good luck as always - DSM

 

[steve]

It's likely overkill but when I remove or change the power transistor I clean the mounting bracket and attach the PTM with heatsink compound. If the bracket is corroded, it gets blasted, wet sanded so the mount pad is smooth, masked off for the transistor to mount on bare metal and painted. If I could I'd replate it rather than paint.

Quite a bit of current is being switched and moving the heat generated away from the transistors and into the bracket will extend the transistors life.

 

[DSM1G90]

Interesting to read of this tip above. Thx, Steve, for the tip.

One could then use, after cleaning the bracket surface down to metal shine, is to put some "Arctic Silver" computer CPU mounting heat sink compound on the bracket prior to mounting the transistor on the bracket, for the bracket of my old unit was pretty gnarly looking.

The new unit that I ordered, came in on a new and shiny bracket which should be able to do good as a heatsink being tied to the head.

Then could I add to the overkill?: Wonder if one could attach a CPU heatsink and fan assembly to the transistor since most of the fans do run 12VDC, or just the large fin heatsink by itself to keep that transistor at nominal temperature?

Now, a side question: With the bracket being mounted to the head, isn't this defeating the heatsink properties of the bracket in the first place since the bracket is supposed to draw the heat away from the transistor? I see a self defeating process here if so.

thx-DSM

 

[luv2rallye]

Now, a side question: With the bracket being mounted to the head, isn't this defeating the heatsink properties of the bracket in the first place since the bracket is supposed to draw the heat away from the transistor? I see a self defeating process here if so.

No. PTU generates higher temps. Also heat travels to the denser (and more massive) head metal plus the head is water cooled, the PTU isn't.