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740 Low z injector w/ no resistor pack GOOF... Any input would be appriciated

rukkus

New member
Joined
Jan 26, 2016
Location
ON, Canada
Hello, thread of shame here

I made the mistake of swapping on low z injectors I pulled off a 94 940 turbo parts car I had. I have a +T 89 740 5 speed running LH 2.4.

Prior to the big goof I made, the car ran fine, apart from the occasional stall when coming to a full stop on a cold engine. Previous owner had installed ev6 style high z red injectors that (I think) came off an s70.
New Bosch turbo black stripe main pump replaced last year as well as fuel filter. And in tank pump is what I assume is the stock VDO unit.

So I installed the low z injectors, tried to fire up the car and no start. Wasn't sitting there cranking for long, but concluded that the ecu fried the injector driver after doing a little bit of research.
I swapped back in the original injectors I had, with the 'new' ICU and ECU from the 94 940 turbo parts car. Everything should be back to normal at this point. Car had a very hard time starting, and with the help of some ether, I got it running. Ran very rich though. Two days later, It left me stranded at work.

-i hear the pumps priming, although I haven't been able to check fuel pressure. Fuel rail doesn't have the Shrader valve, I do have a spare that has one, so that's next on my list.
-There is spark, although took the plugs out, they were covered in soot and fuel. Cleaned them thoroughly with a brass wire brush with no real difference in start attempts.
-Timing checks out, all marks are aligned.
-Tried swapping in a spare AMM, voltage regulator, FPR and the corresponding IACV in consecutive order.
- Radio suppression relay should be ok, I feel it click while I plug it in and out while ignition is on. Had a spare one I tried too.
-I tried the test while having the ignition on, and unplugging one of the injectors, I didn't hear a click.
-I did find a burned out fuse on #11, but unsure whether that happened before or after the incident. Replaced it with no difference

I'm just very puzzled with what else could have happened considering everything is more or less back to how it was, could have a short in the wiring somewhere. I haven't done a whole lot of electrical trouble shooting, not exactly sure where to start there so any input would be appreciated.

Thanks
 
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Yea definitely planning to repair the old ecu, but I would have thought if I just replaced the old ecu with the good spare one I had, should just fire back up and run. With everything back to how it was before the injector swap.

I was worried about damaging the plugs, used the softest brush I had on me at the time. Just to see if cleaning the soot off would change the characteristics starting attempt.

It'll fire, and run extremely rough, as if only a couple cylinders are firing. Have another set of plugs I'll try, but just want to make sure I don't pooch those too
 
Have you used some injector noid lights (or their home brew equivalent) to determine that all 4 injectors are actually firing?

I have one ordered, should be here by tomorrow.
When the car did run for the 2 days with the new ecu in there, I did hear the injectors click as the car ran. With a screwdriver to the ear.
Car ran very rich, light black smoke on idle, so I may have just ruined the spark plugs?
 
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I have one ordered, should be here by tomorrow.
When the car did run for the 2 days with the new ecu in there, I did here the injectors click as the car ran. With a screwdriver to the ear.
Car ran very rich, light black smoke on idle, so I may have just ruined the spark plugs?

Spark plugs are likely toast; but, that is the least of your issues and a low cost problem to fix. If the plugs come out dirty, save yourself the money on the noid lights because fuel is getting into the cylinders.

Since you are mixing and matching stuff, do you know that the flow rates on the red injectors match up with the flow rates on the original low impedance injectors or that they have similar offset values.

Without knowing what other modifications have been visited on the car, it would seem that the better starting point would be to use your ECU from your 1994 parts car with the low impedance injectors from the 1994 parts car and the injector resistor pack from the 1994 parts car (or reinstall the 1989 resistors since the '89 car would originally have had low impedance injectors). If the matching ECU and injectors does not resolve the problem (assuming that they work) then you at least know that the problem is elsewhere.
 
Spark plugs are likely toast; but, that is the least of your issues and a low cost problem to fix. If the plugs come out dirty, save yourself the money on the noid lights because fuel is getting into the cylinders.

Since you are mixing and matching stuff, do you know that the flow rates on the red injectors match up with the flow rates on the original low impedance injectors or that they have similar offset values.

Without knowing what other modifications have been visited on the car, it would seem that the better starting point would be to use your ECU from your 1994 parts car with the low impedance injectors from the 1994 parts car and the injector resistor pack from the 1994 parts car (or reinstall the 1989 resistors since the '89 car would originally have had low impedance injectors). If the matching ECU and injectors does not resolve the problem (assuming that they work) then you at least know that the problem is elsewhere.

So the red injectors I have been using for the past year are 315cc, part number #0280155759. Cant say that I know the offset value compared to the 940 turbo ones.
They're high impedance so to my understanding the 940 spare ecu I had should have no problem running them.
Unfortunately I sold the car without thinking to snag the resistor pack.
I'm thinking now, since I have them laying around, using the stock na yellow top injectors out of my 93 240, just to see if there's a change, and a different set of used plugs that I know work. I know the flow rate isn't up to the task for a turbo car, but just to get it started.

As for modifications, it's a pretty stock 740 +t, using a 15g @8psi.

I initially wanted to swap out the s70 injectors, so I can get them cleaned and maybe flow tested. Car always ran a little rich (don't have a wideband to know exact figures) and idle wasn't the smoothest.
 
Isn't there a relationship between the AMM and the injector size?

You can't change injector sizes Willy Nilly, as the ECU can't compensate.
Doesn't compensate in open loop....

Injector size is a constant and for fueling to be correct it has to be within an expected range.

If you have the OEM AMM, I would use injectors that are the same size as original equipment.

Example:
I bought a Neon (to flip) that ran like crap until it warmed up and got bad mileage.
I discovered someone had swapped the injectors from the original 19# to DOHC injectors which were 21#.
I put 19# injectors back in it and it ran perfect.
 
Isn't there a relationship between the AMM and the injector size?

You can't change injector sizes Willy Nilly, as the ECU can't compensate.
Doesn't compensate in open loop....

Injector size is a constant and for fueling to be correct it has to be within an expected range.

If you have the OEM AMM, I would use injectors that are the same size as original equipment.

Example:
I bought a Neon (to flip) that ran like crap until it warmed up and got bad mileage.
I discovered someone had swapped the injectors from the original 19# to DOHC injectors which were 21#.
I put 19# injectors back in it and it ran perfect.

The s70 injectors I've been running are just about the same flow rate as the stock 940 turbo ones. They are the EV6 style, so a little more modern, the different spray pattern could make the difference in how smooth the car runs.

But as I stated above, I ran the car in this set up for a year with no issues, so I'm confused as to why it won't run with the new ecu. Need to do some testing with the volt meter, if anyone has any guidance on what resistance/voltage values to look for in a good working order Turbo ecu, that would be much appreciated. I'll continue researching though.
It's a white label, ending in 964
 
Need to do some testing with the volt meter, if anyone has any guidance on what resistance/voltage values to look for in a good working order Turbo ecu, that would be much appreciated. I'll continue researching though.
It's a white label, ending in 964

The ECU is a digital device. Testing inputs and outputs with a voltmeter or an ohmeter is not going to yield much / any information about the ECU. If the ECU is causing the fuel pump to go through its prime cycle and you have confirmed that the injectors are opening and closing when the engine is cranking the ECU is likely operational.

It is more likely that the wiring associated with the ECU may be damaged, perhaps when you did the switch. Have a look at the plug on the ECU to check for damage in the pins. Another good place to start would be to do an end to end check on all the wiring between the ECU and the sensors.

Did you ever check the fuel pressure? The FPR on my 1987 745T had an overnight failure resulting in a high rail pressure causing starting and drive ability problems (and a stinky hot catalytic converter).
 
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