Turbo7MN

So I posted a while back about the reman I dropped into my 86 base being messed up. Well, I'm 99.9% sure it's running on one rotor (shakes like crazy at idle, no power when driving) but we compression tested it tonight and both rotors read exactly the same. The motor's still good apparently.

So now we need to figure out why it's running on one rotor if the compression's good. We looked at both leading plugs. The one in the front rotor is pretty black and coated with carbon. The rear plug is clean as can be. This might sound stupid but I want to be sure - which rotor do you guys figure isn't firing?

We checked spark, all the plugs are getting it just fine.

Oh, and after we compression tested it, it refuses to start now. I pulled the EGI fuses when we checked it and it doesn't feel flooded. It just won't start. I'm not too worried about it though, as long as the block's okay we can work with it.

So, any ideas on why just one rotor is firing even though compression is the same on both of them? And yes, we also did remove the valve from the compression tester so it read the bounces instead of holding max pressure.

Thanks in advance, really looking forward to having this car running again.

-Darren

kustomizingkid

iTrader: (2)

I think you flooded the motor, probably didn't pull the right fuses.

Turbo7MN

I know what cranking the motor feels like when it's flooded. It ain't flooded.

But you already knew that, seeing as the car is sitting in your garage.

-Darren

kustomizingkid

iTrader: (2)

No ****, hopefully we can figure this dang thing out.

Elbi

iTrader: (1)

Have you checked for fuel?...you might not be getting fuel to the rear rotor thus causing to only fire in front(maybe). If your compression is good then your seals should be fine so it has to be a minor issue. Not 100% sure but look into it.

SpeedOfLife

iTrader: (16)

mixed up plug wires for one rotor? they'd still spark, just maybe at the wrong time but you probably couldn't tell just by looking

RotaryResurrection

iTrader: (8)

fouled plug most likely, or a bad injector not firing.

Chris RX-7

^ I was thinking that one of his primary plugs got fouled... happened to me after work one time. Had to drive 2 miles very very slow back home.

RotaryResurrection

iTrader: (8)

Usually if you foul a plug, but manage to get the engine started, hold the revs up around 3-4krpm for about a minute and the plug will heat up and start firing again intermittently and then completely. But it is still likely to foul at idle or cold startup later on.

Turbo7MN

The plugs are brand new. We also verfied the plug wires are on correctly, so that's not it.

My guess is it's not getting fuel. Seems odd though, I used the injectors that I have been running for three and a half years with my other motor. Maybe a connector slipped off when we were putting it back together. We'll probably take off the UIM and see what's up, and I'll grab some new plugs just incase.

-Darren

SpeedOfLife

iTrader: (16)

new plugs can still be faulty or foul up, but at least usually you can see fouling evidence by looking at them so just make sure you've checked.

MazdaMike02

iTrader: (4)

My guess is an injector is bad, maybe the connector fell off or its just not injecting fuel into the motor.

kustomizingkid

iTrader: (2)

I'm thinking that it's something fuel related.

It's really weird how we compresion tested it and now we get nothing at all. I think it's time to pull the dang upper manifold off and recheck everything.

Spectator

iTrader: (1)

If the rotor is not firing up, check if you have spark. And does the plug smell like gas?

You'll have your answer.

pfsantos

iTrader: (1)

If you have low resistance injectors (86-some88):

Could be Fuel resistor under air filter area near shock tower maybe not sending current to all injectors. Check to see if continuity (with some resistance) exists from one wire to all four injector wires.

TweakGames

iTrader: (3)

I had the same problem as you and I had my injector wires going to the wrong injectors... Just throwing that out there.

chatchie

iTrader: (22)

Crank it and pull the plugs from the non firing rotor, they should be wet. If not there's your problem.

Turbo7MN

I already said we checked spark, we're good there.

Sounds like the most logical conclusion at this point is no fuel getting to the rear rotor. I didn't specifically check to see if the plugs were wet when we had them out but I'm pretty sure the clean one was totally clean - no fuel. Hopefully tomorrow I'll have a chance to pull the UIM and recheck everything.

Thanks for the help.

-Darren

kustomizingkid

iTrader: (2)

I wonder if we hooked up the lower injectors wrong? Your damn car is making me a little mad.

I just don't understand why it stopped working completly after the compression test. Definetly bring your ohmeter over when we work on it next.

Turbo7MN

Problem solved.

The whole manifold assembly and injectors came off the old motor which ran great before the swap so it seemed odd to me that it would be a bad injector. We took the UIM off and couldn't see any mistakes in the reassembly. The problem had to be a little less obvious. Sure enough, the contacts inside the rear primary connector got rammed back somehow and weren't making connection with the injector. We spliced a good one in from one of my spare harnesses and it fired right up. She drives great now.

Thanks for the help guys. I can't believe after two years this thing is finally running at 100% again.

-Darren

kustomizingkid

iTrader: (2)

I was lucky to spot that connector, it's a good thing ya had someone who knew what they were doing on the job.

Thruan

just for everyones info, a quick and easy way to figure out which rotor/piston isnt firing is get it running if posible, if not just crank it and let it try to start, then disconect the plug wire/s to one rotor/piston at a time..

if its running it will stop running/ stumble even worse if u pulled the plug on the running rotor/piston, if u pull the plug wire on the 'bad' rotor/piston there will be 0 change.. easy way to narrow down the problem..

hopefully that makes sense to everyone