Sideways7

iTrader: (7)

I recently swapped in an engine from a parts car but haven't gotten it to run right. Today I went to check the compression again to make sure nothing happend since I checked last, and it was up to 85-90 on all 6 faces (better than last time I checked). I also noticed that the front plugs were pitch black, while the rears where shiny and new (about 50-100 miles on all plugs). Could one of my spark plug wires be bad, or is there another problem?
I attached a pic of the plugs. Left is the front leading, right is the rear leading.

Sideways7

iTrader: (7)

Ok, so I tested the wires and BOTH of the leading wires are about 9k ohms. The FSM spec is 16k ohms. I would think if this was the problem it would affect both plugs, not just the front. So does anyone have any other ideas?

JCurry

iTrader: (6)

Are the shiny plugs wet witih fuel?

Sideways7

iTrader: (7)

Well, the car hasn't been started in several weeks (busy with school, but now finished) so I don't think they would be wet regardless. But no, they weren't wet. The rear primary looked basically brand new, and the rear trailing had a bit of gunk on it (I think from after I pulled it out) and looked basically new after wiped it off. As seen, but front plugs were black. I have tested for spark and I know that all 4 plugs are getting spark so the coils are fine. The injectors were recently cleaned so they should be fine. I recently replaced the injector plugs, but I am pretty confedent that they are good.
Also, there is a chance that when I first started it something happened and the plugs have been bad the whole time, but its pretty unlikely. Its raining right now, but I'm gonna try to fire her up later and see what happens with new plugs, just in case.

1987mazdarx7

hmm maybe your not getting fuel. might be a fuel pump or your fuel filters dirty or possible you injectors.

Sideways7

iTrader: (7)

Well one rotor is running fine, so I doubt its the pump or filters. Also, I just replaced all of the filters.
Its something that is just happening on the front rotor, as the rear seems fine.
Just to be clear, the car will start and run, just not very well.

1987mazdarx7

Tps?

RotaryEvolution

iTrader: (30)

after 100 miles that rear plug should at least show some signs of firing, seems to me like you have the infamous "faulty primary injector clip" gremlin. does it feel like it has normal power or like it is running on 1 rotor? the forward plug would be dark if this was the case since it is powering the whole motor and loading up.

Sideways7

iTrader: (7)

It is most definately running on one rotor. I guess that makes sense about the rears looking so good. Now that I think about it its probably been more like 50 miles (if that) but there was a good bit if idling when trying to fix stuff (timing, vac leaks, etc.)
I replaced all of the injector clips before I put in the motor, so maybe I messed one up. Is there another reason that the clip might be bad?
Maybe its time I invested in some noid lights.
Edit: tps is in spec as well.

KompressorLOgic

iTrader: (6)

if you go over 3800 rpm does it run better?? i had a primary injector that was clogged or something and it would run like soewhat on 1 rotor

and then start driving alot better when above the 3800rpm

i also noticed my rear rotor plugs looked like they were running lean compaired to the front ( in my case the rear one was bad, replaced it and it ran great)

Sideways7

iTrader: (7)

Nah, it still pretty much runs like *** above 3800. It does at least have a tiny bit of power, though, as opposed to down low.

scathcart

The tests I use for testing spark plug wires are to check the resistance with a ohmeter of the ledas, then check the resistance of the insulation with a Megger @ 1200V. If I suspect a lack of noise suppression, its easy to determine how bad it is with a piece of wire run parallel to the lead and an oscilliscope.

Then again, when i doubt, replace the wires.
I only run the stock wires, even in performance applications. I've had a few applications where I got rid of ignition break up in the upper rpms with brand new aftermarket wires (MSD, for example) simply by putting on new OEM wires. At $40 for a set of four, they are also the best value.

Sideways7

iTrader: (7)

You lost me... No idea what a megger is. Also, could you elaborate on the o-scope testing?
Anyway, I don't really have any reason to suspect the plug wires. I just saw that someone was having a similar problem to me caused by them and thought it might be the problem. They worked perfectly fine with my old engine and have about 25k on them. All they did was sit on my shelf for a year, so I don't see why they would be bad.
I think I'm gonna check out the injector clip tomorrow since that looks like the likely culprit. It was actually what I was thinking originally until I saw the thing with the plug wires. Looks like I gotta pull of the damn intake once again. I'm starting to get pretty good at it...

scathcart

Megger: Mega-ohmmeter. Used for testing the resistance of wire insulation to check for breakdown and leakage. They output 600-1400V, typically use a hand crank.

I use an oscilliscope b/c I have one handy to check for induced voltage in an adjacent wire. I only do this if I suspect the wires have a severe lack of noise suppression and are inducing currents in adjacent wires. Testing this is as simple as placing a hunk of insulated copper wire right beside the ignition lead, revving up the car, and watching the scope for voltage. More voltage induced = bad.
You could also use an AC voltmeter.

Sideways7

iTrader: (7)

Ah, ok. Hopefully I won't have to mess with that stuff. The only o-scopes I have access to are up at the college, and I don't think they would let me take it home

KompressorLOgic

iTrader: (6)

since u will have the upper intake manifold off to inspect the injector clips on the primarys.

try swaping each primary( lower rail) injector with each secondary(top rail) injector. ( then if it runs great below 3800 then u know it is an injector, and the bad one will have been moved to the top, and is easily changeable)

pengarufoo

run the car again, then pull all the plugs shortly afterwards.


if the rear plugs arent wet theres no fuel on that rotor.

if they are wet theres no spark on that rotor.

it's that simple :P


If there is no spark, check to make sure the plug fires when grounded to that rotor housing... sometimes when you check spark you ground it to some part of the chassis and it will work fine, you might need a better ground to that rotor housing.

If there is no fuel on just the rear rotor either the injectors are not working (clogged or stuck?) or you have an electrical issue in the efi circuit.

Sideways7

iTrader: (7)

Thats an excellent idea, I will definately try that.
Also, I just had the injectors cleaned and flowbenched, so I don't think they are clogged.

pengarufoo

if it turns out you're not getting fuel on the rear rotor it could be as simple as the pin getting pushed through on the primary injector clip... wouldnt be the first time that has happened.

another thing that happened once before is the primary injector clip got fuel inside of it from a leaking fuel rail and it was preventing the injector from firing, not sure if it was shorting or resisting, but blowing it all out with the compressor and reassembling fixed it.

but obviously the first thing you have to do is narrow it down to a fuel or spark problem.

RotaryEvolution

iTrader: (30)

he already mentioned the plugs being dry after having been run so i would rule out no spark at that rotor. my suggestion is tear the manifold back apart and inspect the clips and strap the injectors to the rail and use a spare CAS with the ignition on to see if both injectors are firing, be sure to disable the coils so there is no spark though.

Sideways7

iTrader: (7)

I'm going to try the spark on the housing thing and if that works, then I'll pull off the intake and tie the injectors to the rails and test that way. Not sure when I'm gonna get ot it, though, since its nasty and wet outside today.

Sideways7

iTrader: (7)

Ok, so I think the problem is bad grounding to the rear housing. I never actually said the plugs were dry after being run, I just said that they were dry but I hadn't started it in a few weeks. Today, once the weather cleared up, I went out and hooked everything back up and tried to start it. It wouldn't start for anything, but I did check the plugs afterwards. The L1 plug was perfectly dry, while the L2 was a little wet with fuel. So its obviously getting fuel to the rear rotor and since they looked new, its not getting spark. I tested spark with the screwdriver on the fender method, and all 4 had spark. I guess what that leaves is what pengarafoo described where there's not a good connection, which I will check as soon as I get a chance. I assume that this is from bad grounds.
So now my question is: are there any particular grounds that would cause this if unplugged?

Sideways7

iTrader: (7)

Ok, so I got the idea that I could test if the rear plug is getting spark with my timing light. I hooded it to the L2 wire and its flashing. So does this mean that the rear plug actually is getting spark?