Everything is there, but we cant get this 7MGE to start

[90T04]

I am helping a friend get his car running that he just purchased midway through a HG job. He has already replaced the ignitor/coil assembly, the distributor, all plugs, wires, cap and rotor.

We have fuel pressure, but it seems the spark is what we are missing. It wont start on ether. We have checked IGF and IGT wiring from the ECU to the Ignitor, but unfortunately we dont have a O-scope to check those signals.

We have verified all wiring from the distributor, ohmed out Ne and both G sensors at the ECU and all wiring is good. He has been over the cam timing several times and we know its ok.

Battery voltage is good, we have checked B1, B, IGN, and BATT to the ECU as well as the Grounds.

The Ignitor case ground is good, and we have tried rotating the distributor every tooth to see if it will help. We have also checked the timing mark on the crankshaft pulley to make sure it hasnt rotated on us.

Compression is good at about 150 psi across the board. I know the ECU will cut fuel after several IGT outputs and no IGF return. When does it resume fuel delivery? After the key is cycled?

If anyone knows what we are missing please let me know!

Thanks!

---------- Post added at 11:53 AM ---------- Previous post was at 11:51 AM ----------

Oh, I forgot there are also no codes

 

[jdub]

Does the CEL come on when the key is turned on?

 

[90T04]

Yes it does, and when cranking the tach flutters just a little bit

---------- Post added at 12:20 PM ---------- Previous post was at 12:17 PM ----------

And, I forgot to mention that he has tried another ECU and it does the same thing

 

[jdub]

Check to make sure the ECU grounds in the intake manifold are secure.

Sure the cam timing is not 180 degs out? (easy to do)

 

[90T04]

Yep, grounds are good. Dropping .1volts when cranking from the battery to the grounds at the ECU.

As far as the cam timing goes, the cams are in their center pins and pointing straight up when the crank pulley is on the 0 mark. Then the distributor is put in per the TSRM instructions.

 

[jdub]

Did you verify that the #1 piston is at TDC with the crank pointing at zero? Use a small diameter wooden dowel about a foot long in the spark plug hole - as the crank is turned, dowel height should max at the damper zero index. The dizzy should be pointing at the #1 plug wire contact.

 

[90T04]

Yep, thats how we verified that the mark on the crank pulley was still valid. I will have him check it again just to verify.

 

[90T04]

Okay we just verified that the cam timing is all correct and the ignition timing is where it should be.

I am going to try and find someone who has a DSO I can borrow to find out what is missing here. Im thinking we may have got a bad replacement ignitor.

 

[jetjock]

Did you check the power side of the ignition circuit?

Btw, nice to see someone who understands how things work and knows how to troubleshoot them correctly. My compliments...

 

[90T04]

Hey JJ, thanks for your compliments:icon_bigg


Yep we did check the power side of the circuit, we have battery voltage to the igniter and ignition coil when cranking.

Im going to head back over to his house now and see if I can come up with anything,

thanks for your guys help

 

[jetjock]

You're welcome. I don't hand them out easily

Fwiw the coil and igniter can be checked by flicking the primary (IGt) to ground (do it quickly) while looking for spark at the coil secondary...

 

[90T04]

Ah, wish I would have known that before I left!

Well I just got back from messing with the car for another couple of hours. All I really found out is that I still need a scope to properly diagnose this one. The coil/igniter, ECU, and distributor he got are all ebay parts so I am assuming that one of them is bad and further complicating things. Also the previous owner was not too kind to the harness we are dealing with that obstacle.

I did find that the coil is firing but very infrequently and intermittently. When it does start to fire, it will fire approximately one spark in one or two seconds of cranking the engine. But it still doesnt sputter or act like its going to start.

Just checking the Ne and G signals at the ecu with my meter on Hz I found that there is some sort of frequency coming from the generators in the distributor but the amplitude, etc of them I cant be sure of.

We played musical parts for a while and then when nothing changed, we decided to hang it up and come back with the right tools.

 

[jetjock]

Yeah, sometimes a scope is the only tool that'll do the job. NE and G are reluctor based btw. Output is sinusoidal and needs to be a minimum of 1 volt p/p at cranking speed to bias the ecu's A/D converter. They're usually much more unless speed is low, magnets are dead, or air gaps excessive. Still might want to check the coil and igniter the way I said. Every flick of IGt to ground should generate a fat blue spark on the secondary. If it does look elsewhere. Good luck...

 

[90T04]

Thanks for the help, I will definitely do that igniter check. That does not verify that there is and IGf coming out of the igniter though, right?

The chances of having bad pickups in 2 different distributors are pretty slim, but I have seen stranger things.

 

[jetjock]

No, it doesn't unless you measure for it. I was just focusing on the no spark because once you get past that IGf should take care of itself. You know, for this kind of stuff a logic probe works too. Not as good as a scope but much cheaper. It'll at least tell you if pulses are there.

 

[90T04]

Yea I actually have a logic probe at work but honestly I thought this was going to be an easy fix and didn't bother bringing it home.

 

[Nick M]

I did find that the coil is firing but very infrequently and intermittently. When it does start to fire, it will fire approximately one spark in one or two seconds of cranking the engine. But it still doesnt sputter or act like its going to start.

Just checking the Ne and G signals at the ecu with my meter on Hz I found that there is some sort of frequency coming from the generators in the distributor but the amplitude, etc of them I cant be sure of.

You have to run down that DSO. I still see them for sale on ebay at a fraction of new.

 

[base_tpk]

i have this same exact problem mine cranks but the injectors wont open or at least thats what i think i cheked the grounds in the intake and everything but yet i still have the same problem i tested the injectors and they all click. im desperate now !!!!!

 

[Nick M]

Does plug number one spark when cranking?