Engine Backfires After Changing Injectors

[Quinthirty]

Mechanic changed the injectors to 17lb M50s, flow tested, new seals and filters, ultrasonic cleaned. Its running on a 24hp Ebay chip.

Its hard starting. When it starts, it won't idle, sputters, backfires, emits black and white smoke, and dies. Rev high or low, it sputters and dies. It seems that its getting flooded.

Before I replaced it, car was ok with Ebay chip and stock injectors but there was a slight tumble on the idle, without the RPMs changing at 800 RPM.

1. Backfire due to vacuum leaks?
2. Old pintle caps stuck in the combustion chamber?
3. Injector not seated well, thus, vacuum leak?

What else should I check on?

Thanks!

[jeffnhiscars]

Someone should know if you are missing a pintle but also could be he reversed the fuel lines or miswired the injectors (although that should not be easy to do). Id start there.

[Chruby99]

are all the spark plug wires attached to cap in the correct position

[Quinthirty]

are all the spark plug wires attached to cap in the correct position

Yes, they are. In fact, returned the old injectors and the problem still exists. My hunch is that its electrical, and has something to do with the injector wiring harness. Replaced the ECU and returned it to stock with the stock injectors, and now the car still backfires, and won't idle. When we removed the plugs, all were wet with fuel, so its flooding. Absolutely at a loss now especially with the misfiring.

Problem is, it was perfectly fine before we changed injectors.

AFM is new
Distributor cap is ok
ECU is ok

Grounding? Where is the ground for the injector wiring harness?

[Quinthirty]

Now running after fixing electrical issues.

[hahaitzskippy]

ignition timing? fuel regulator? i dunno

just throwing ideas out...

[fannman]

what was the cause of this issue or did you resolve it? Im having the exact same thing happen to me. It has "carb farts" along with the spark plugs being coated in fuel like its running really rich. I am running m50 injectors as well.

[Quinthirty]

Mechanic mentioned a number of things, but what I observed was he forgot to remove the negative terminal BEFORE he replaced the injectors. Somehow, it ruined the ignition coil, which was the cause of the backfire. Coil was perfect prior to replacement.

Backfire checklist. Possible causes: unburnt fuel, incomplete / no spark, stuck valve

1. Check coil
2. Check each spark plug
3. Check connections of injectors
4. Check impedance of injectors
5. Reset ECU
6. Turn crank and see if a valve gets stuck (maybe pintle caps fell off, etc.)

Misfiring
1. Check grounds: ECU, main C101
2. Check AFM flap
3. Check distributor cap

Hope this helps.

I'm not sure about your case, but mine has a chip. Do you have one? I read somewhere here that M50 injectors will not run well on a stock chip. Stock injectors will run on any chip well though.