LT5 Misfiring at All Speeds

[XfireZ51]

Paul,

For purposes of accuracy, the ECM does not actually issue the firing command to the secondaries. The ECM energizes the secondary injector power relays via ground, which in turn powers the secondaries. The secondaries then use the primary injector firing signal. So there is no unique signal coming from the ECM to the secondaries themselves.
Again, another "work-around" from the L-98 avoiding the need for injector drivers on the ECM motherboard.

[cvette98pacecar]

Paul, I do not think you could inadvertently plug a secondary injector plug into a primary injector. The wiring is not long enough. it is hard enough to get the plugs on the injector as it is, I cannot imagine how hard it would be if you crossed the plugs

[Paul Workman]

Originally Posted by XfireZ51

Paul,

For purposes of accuracy, the ECM does not actually issue the firing command to the secondaries. The ECM energizes the secondary injector power relays via ground, which in turn powers the secondaries. The secondaries then use the primary injector firing signal. So there is no unique signal coming from the ECM to the secondaries themselves.
Again, another "work-around" from the L-98 avoiding the need for injector drivers on the ECM motherboard.

Righto! Poor wording on my part. Better to have said the ECM powers the secondaries via relays #1 and #2, as "explained" by the schematic... (No points for rushing)

[Paul Workman]

Originally Posted by cvette98pacecar

Paul, I do not think you could inadvertentlywhatg a secondary injector plug into a primary injector. The wiring is not long .
Though. it is hard enough to get the plugs on the injector as it is, I cannot imagine how hard it would be if you crossed the plugs

Agreed. Swapping isn't my experience either. Jon brought it up, and for what it lacks in probability the symptoms fit the swapping scenario like a glove

Curious to see what actually unfolds...

[Big D]

I have an unmodified 90 and I have the 90 SM. I went to the library and got a diagram for the primary circuit which shows the primary wiring and the "splice S127" i believe. I also have the LT5 Fuel and Emissions Course book which is somewhat helpful. Not sure what my next step will be, was thinking turning it over and checking to see if i am getting voltage to # 6 at the injector. Shouldn't take but a couple of turns to verify. From the schematic it looks like i should be looking for a ground from the ECM on terminal A of the injector. Since i can shoot the wire from the yellow ECM connector to the injector and it is good I should be able to look for the ground on the back of the ECM while i turn it over, doing this would also NOT fire the left bank injectors since I haven't removed their electrical connectors, thus avoiding sending fuel into the cylinders. Also will check for 12 volts on the B side of the injector with the key on. Hope to look at this tomorrow if the chores don't overrule.

[Big D]

I have an unmodified 90 and I have the 90 SM. I went to the library and got a diagram for the primary circuit which shows the primary wiring and the "splice S127" i believe. I also have the LT5 Fuel and Emissions Course book which is somewhat helpful. Not sure what my next step will be, was thinking turning it over and checking to see if i am getting voltage to # 6 at the injector. Shouldn't take but a couple of turns to verify. From the schematic it looks like i should be looking for a ground from the ECM on terminal A of the injector. Since i can shoot the wire from the yellow ECM connector to the injector and it is good I should be able to look for the ground on the back of the ECM while i turn it over, doing this would also NOT fire the left bank injectors since I haven't removed their electrical connectors, thus avoiding sending fuel into the cylinders. Also will check for 12 volts on the B side of the injector with the key on. Hope to look at this tomorrow if the chores don't overrule.

[Big D]

Ok, the saga continues. First, I believe I have found the problem but ran out of time last night to fully verify. Looks like I have a bad connection at the ECM connector, probably a pushed back socket at A8 or I oversized it so that the pin doesn't make good contact. Now the story. First I disconnected the electrical connectors from all of the injectors. Then, using a 9 volt battery, I checked the # 6 injector and the # 2 injector as a knew the # 2 was good. I jumpered from the injector to the battery negative side and then touched the positive side and got a good click each time. Did the same to # 2 for comparison and it acted the same, so I ruled out a faulty injector (which I basically had already). Next I pressurized the fuel rail and did the battery check again. Looking down the injector port you can see the injector spray end and tapping the positive produced a nice spray out of the #6 injector, same with # 2, again verifying the good injector. Then I re-connected the plenum electricals for my next test. With the ignition module now connected I reconnected the #2 and #6 injectors electrical connectors. I had my assistant (daughter) turn the car over while I looked down the injector port. # 2 sprayed very nicely but #6 did not. So, back to shooting wires. Checked wire from injector to ECM, no problem. Looked into the ECM at pin 8, .7 K ohms. Re-connected the yellow ECM connector. Then I did voltage and ohm checks of each injector connector pins. With the key in the run position, "B" side should read around 12 volts (from the ignition) and the "A" side is looking for a ground into the ECM. I'm assuming here from data I have generated that the "A" side should read about .7 - .8 mega-ohms in this setup. (all "A" side resistance was around this number except for # 6). # 6 showed an open circuit on the "A" side but 12v on the "B" side. Ok, so the "A" side is not getting the signal from the ECM. Removed the yellow ECM connector and re-verified continuity between it and the #6 injector and it was good. Verified .7 k ohms into the ECM at pin 8 and it was good. Checked other injector pins into the ECM and got the same results. Next I jumpered from pin 8 of the ECM to socket 8 on the connector. Went to the injector connector and ohmed out pin "A". It read .7 k ohms. Then I was out of time. I will try and "fix" the socket to get a better connection with the pin and then do the injector test like before. I feel pretty confident right now that the plug is the problem. I'm thinking I might have used a test pin into the connector that was too large when I was first doing my injector tests when this problem first surfaced and the larger pin opened up the socket too much. Will get back at this next weekend, hopefully with good results.

[tccrab]

Boy, talk about deja vu.
I had this EXACT problem a few years ago for the EXACT same reason.

http://www.zr1.net/forum/showthread.php?t=10828

I seem to recall that I bought extra connectors, I'll go dig through my big box 'o spares.
PM me your address I'll mail you a couple, gratis.
I don't have the OEM crimp tools, I had to borrow a set from a former member. If you're careful you can get the job done with just a regular set of pliers.

'Crabs

[Big D]

thanks 'Crabs, I'm hoping to get back on it this weekend and see if I can't get her back on the road, missing all this good weather we are having up in the Pacific N'West. I gotta keep the chores at bay though.

[Paul Workman]

Originally Posted by Big D

I'm thinking I might have used a test pin into the connector that was too large when I was first doing my injector tests when this problem first surfaced and the larger pin opened up the socket too much. Will get back at this next weekend, hopefully with good results.

IIRC, there was a post (by Marc Haibeck??) a year or so back warning about that very thing: be very careful NOT to shove a pin (such as on a VOM probe) into those connectors as over expanding the cylinder (female side) of the connector is a common problem.