Yomanchu

hello everyone I am still chasing this misfire please help. here is a description of what my engine is doing: at cold start up it idles fine once it goes into closed loop the idol is a little erratic. but when I rev it up test 1800 rpm it misses and stumbles. it doesn't have any sort of hesitation when driving nor does it ever stall out or bog down. now here is what I have done to remedy: I have replaced plugs, wires, injectors, upper plenum and throttle body gaskets, fuel filter with a motor vac service, replaced the AFM, set the TPS, adjusted valves and set the timing. check all of the vacuum lines to and from the vsv EGR and back to the TB and manifold. checked all of my engine and Chassis grounds. I have even done a continuity test on the ECM sensor grounds and back to the TPS on each circuit. when I worked in a shop I had the shop foreman help me hook up the vehicle to an engine analyzer and determined that there was no obvious mechanical issues causing the misfire. the fuel pressure was good as said the motor vac machine. we did do an injector balance test and found one injector was going bad that's why I replaced them did not make any difference. I know the plastic intake tube is old and cracked in some places but not close to even solving the misfire issue. just recently had the check engine light on for a code 71 for EGR temperature whatever. disconnected the battery ran it code has not yet returned. also I did manage to hook up the snap on scanner to the DLC and read that the engine was constantly switching from open to closed loop operation or so the scanner said. I found a few engine grounds that were missing but still made no difference. also had to re-pin the EGR temp sensor connector because the wires pulled out. I know there is still a short somewhere but would like a direction to go in before I pull out the whole freaking harness. any ideas please help cuz I am going cross eyed from looking at electrical diagrams over and over.

Buck87

The common grounds to the injectors tend to go bad on these engines and cause weird misses. There are two of them and they are located in the wiring harness. To get access to both of them you will need to remove the intake manifold and unwrap the harness from the front back until you reach to the second common ground. When you get there if they are bad it will probably be obvious, but clean them up and solder them anyway. While you are there it is a good idea to replace the injector connectors here is a link to get those http://www.lceperformance.com/Inject...-p/1062007.htm.
This will take a couple of hours but it is worth a try and a lot cheaper than replacing air flow meters and is a worthwhile upgrade. Check for vacuum leaks and while you have the manifold out of the way clean out and test your egr.

Yomanchu

Hey there buck87. I'm assuming you mean the injectors are grounded to the ECM correct? also if you get a chance can you refresh my memory on how to do voltage drop test? continuity test don't always give definitive answers you know. and with the bad ground for the injectors explain why the injector balance test indicated an injector was failing mechanically? sorry for all the questions bro

Yomanchu

also I have already removed the upper plenum and replace the gaskets when I did the injectors. and I tested the injectors with the Noid lights. that should have given the indication of faulty grounds in the injector circuits correct.

Buck87

If you checked the injectors with a noid light this may not be the problem.
Sooo, I just looked at the schematic from the FSM and there are actually 4 sets of splices in the injector wiring 2 from the resister that is mounted on the firewall and 2 from the ECU and I assume that the ones to the ecu are the ground. Any of these splices going bad could cause a problem. They are spliced together with a crimp. I eliminated the crimp and soldered the wires together. My injector connectors were in bad shape and since I was redoing the splices I also upgraded those.
The injectors have a solenoid in them so a resistance check across the injector will tell you if the solenoid is intact but the noid should tell you the same thing.

Yomanchu

my mistake buddy. I didn't use the Noid lights. I actually used a DSO with what looked like an amp clamp around the injector wires and I was told that it was an injector balance test. this test was supposed to be more accurate and definitive of a test to determine functionality of the injectors and ultimately would trump the Noid light test. the voltage pattern on injector number for was so radically different than any other of the other injectors that I just assumed that it was a bad injector rather than any sort of electrical problem. considering I did do a continuity test for the injectors from ECU to ground. you did answer a couple of questions for me though. now that I think about the resistor you mentioned on the firewall. If the resistor is bad would that explain the erratic readings I got from the balance test or would the resistor being bad cause the injectors to not pulse at all. not sure if I mentioned this but when I was inspecting the engine and Chassis grounds I found one ground missing one from the cylinder head to firewall and when I did hook up that ground wire, then turned the ignition on there was spark and electrical short somewhere near the battery or fuse box area. my fuses are good my relays are good had to replace the battery though. my question to you now is when that happened could I have shorted out the resistors on the firewall? I know this is a lot of s*** to think about. I've been doing it for a year. thanks again for your advice.

Buck87

The resistor feeds all of the injectors with constant power and the ECU opens and closes the circuit. Sounds like the ecu and the resistor are working correctly.

Yomanchu

Oh I thought you meant the resistors were grounded to the firewall. now that I think about it, that doesn't even make any sense. Duh. I used to have the factory service manual and all of the electrical diagrams on a PDF. Anyway, it looks like I'm pulling that harness out. Do you know of a way I can pull the harness without removing the upper plenum? and also I just remembered when I replaced the injectors I noticed that the ones I pulled out we're not the same as the OEM injectors that I bought. long story short I ran the part numbers and they came back as 5 liter Ford injectors I then cross-referenced both those and the OEM injectors they came back compatible, however, adapters were used for the injector wiring. the plugs didn't exactly click together you know. maybe that could have caused some sort of resistance in the wiring?

Buck87

http://www.lceperformance.com/Inject...-p/1062007.htm