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Don
Don, Ford Senior Master
Category: Ford
Satisfied Customers: 987
Experience:  ASE Master certified, Ford Senior Master, 20 year experience
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1995 Ford F-250: Guys..Engine code H, 5.8 liter, GVW - >8600

Customer Question

OK Guys, Here's a tough one. 1995 Ford F-250, Engine code H, 5.8 liter, GVW - >8600.
Problem: MIsfire under light acceleration and above. Drops injector pulse on one bank ( #'s 2,3,6,7)(white wire to ECU). Idles perfectly. All injectors working.
Parts replaced: Complete secondary ignition (cap, rotor, wires, plugs and coil), Distributor (twice), Remote mounted TFI (twice), ECU (twice).
Diagnostics Done: Checked and verified all signals present to TFI and ECU. Using a MODIS to perform tests. Cut the white wire to check for Injector pulse at ECU. Pulse goes away under light throttle. (Light throttle applied while in drive with park brake set.) Looking at data on MODIS, Bank 1 injector pulse looks normal, Bank 2 injector pulse is zero at idle and engine running perfectly.

Has anyone seen this? Could an injector with very low resistance be causing the ECU to burn out on that bank? As in too many amps getting to the ECU?

Brian Harbour, Brian's Auto Repair, A.S.E. Master Certified
Submitted: 4 years ago.
Category: Ford
Expert:  Don replied 4 years ago.
Hi my name isXXXXX think I have an answer for. the only thing that could drop just those injectors is the wire at pin 58 in the pcm connector or pin 13 in connector 101.the white wire. if the pins are loose or the connection on those pins is poor. when you give it throttle the connectors will move slightly and can loose contact. check those pins even if you have to pull them out of the connector and tighten them up a little
Customer: replied 4 years ago.

OK Don.

I went one step further. I replaced that terminal with another one out of an old 60 pin connector. It is gold plated and looked good. No change in performance. Scanner still indicates bank 2 injector pulse at zero. Testing pulse with noid light indicates proper operation. Contradiction here. Engine idles smooth, running on all 8. Ligfht throttle in gear, drops injectors listed before. I DO have a substitute wire for the trucks wiring harness in place to eliminate that possibility. I am performing the tests at the ECU plug.

Three ECU's, all with the exact same problem. What could cause the injector driver circuit to fail in the ECU? This is a pretty basic system. Timing and synch done by the distributor and modified by the TFI and sent to the ECU for injector control/fuel management.

Expert:  Don replied 4 years ago.
there is also a splice in the harness where all 4 wires from the injectors are spliced into 1. try this make an over lay harness with 4 wires to 1 and run it from the injectors to the computer pin 58 and eliminate all the harness this will tell if it is the harness or the pcm.
Customer: replied 4 years ago.
Got it, I'll do that right now.
Expert:  Don replied 4 years ago.

ok

 

Customer: replied 4 years ago.
OK, I fashioned an overlay harness for injectors #6 & #7. I left 2&3 offline. For testing purposes. Could not find the 4 into 1 connection. My substitute is wired directly to 6 & 7 and to the ECU and the trucks harness is out of the loop. Scanner still shows bank 2 pulse at zero. Looking at injector pulse on the lab scope, they are firing at idle, goes away under slight throttle. Engine runs on the six injectors that are active at idle.
Expert:  Don replied 4 years ago.
lets just check something is your truck a 95 or 96 just say you typed both years in beginning
Customer: replied 4 years ago.

It is a 95

 

Expert:  Don replied 4 years ago.

on the pcm pin what number pin did you splice into

 

Customer: replied 4 years ago.
Pin # XXXXX Pin # XXXXX fires the other set of injectors. I am working with the white wire circuit.
Expert:  Don replied 4 years ago.
good thats what I wanted. if you over layed the wire and eliminated the harness. then the ecu is bad again. one of the injectors or the harness is shorting the ecu.
Customer: replied 4 years ago.

Let me see if you agree with my next step. Replace the 4 affected injectors, build a new harness for those injectors and replace the ECU.

If you will look back, one of the questions I had was: will an injector cause the ECU driver circuit to overload and burn out?

Expert:  Don replied 4 years ago.
the red side of the harness all 8 wires are connected together, so that side can not be the problem. I would overlay all 4 injectors and replace the 4 injectors before i installed the new ecu
Don, Ford Senior Master
Category: Ford
Satisfied Customers: 987
Experience: ASE Master certified, Ford Senior Master, 20 year experience
Don and other Ford Specialists are ready to help you
Expert:  Don replied 4 years ago.
sorry my computer is acting up and I am having a hard time typing and sending answers to you. It is rare but I have seen injectors short ecu. have only seen about 2 in 17 yrs in the dealer
Customer: replied 4 years ago.

Thanks Don. I will replace the 4 injectors and the firing side of their harness. I will have to order the ECU. Should be done with the other work by the time the replacement gets here.

FYI: I am also an expert on this site. I amCustomer A.S.E. Master Certified since 1990. I have 40+ years experience in Domestic and Asian Cars & Trucks.

Expert:  Don replied 4 years ago.
If I can be any more help just let me know let me know how it turns out.
Customer: replied 4 years ago.

Hello Don,

I have replaced the 4 affected injectors, rebuilt the trigger side of their harness all the way to the ECU. (Which had to come from Pennsylvania = Long Wait). Fired the engine with my scanner attached. Still showing bank 2 with zero pulse width. Still drops the same 4 injectors.

Two questions to ponder...

1) What would happen if I tied both banks of injectors together. (firing all 8 at the same time)?

2) What ECU pins are grounds? My wiring diagram in my chilton book does not show me.

Brian

Expert:  Don replied 4 years ago.
for # XXXXX would over load pcm drives. give me a couple of minutes on the ground pins
Customer: replied 4 years ago.

OK

 

Expert:  Don replied 4 years ago.
pins 20,40,60,16,
Customer: replied 4 years ago.
Thanks, XXXXX XXXXX going to test continuity on these grounds.
Expert:  Don replied 4 years ago.
if you can load test the wires
Customer: replied 4 years ago.
You got it.
Expert:  Don replied 4 years ago.
let me know what you find. your right this is a tough one
Customer: replied 4 years ago.

Here are my test results.

All 4 ground pind show zero ohms.

Loaded the 4 with an old rotating beacon light, drawing between 5 and 10 amps.

Voltage drop is: Pin# XXXXX = .54, Pin# XXXXX = .64, Pin# XXXXX = .64, Pin# XXXXX = .71.

All these seem to be acceptable to me.

Your thoughts?

Expert:  Don replied 4 years ago.

yes all of the ground are with in ford spec. I have gone over and over the wiring. what does the iac motor do when this happens

Customer: replied 4 years ago.

IAC goes to 100% at start-up. rolls back down to 42 - 45 %. Keep in mind that this is a very dirty throttle body. IAC varies accordingly with TPS changes. CT TPS = 1.07v. TP goes up and IAC follows. IAC has no different reaction when running on 8 or 4, other than normal allowance to maintain idle.

Expert:  Don replied 4 years ago.

here is the issue injectors 1234 are powered together but 2468 are grounded. so the only thing that can cause 2468 to bow out is the injector to pcm wires. when you over laid the wire did you use a new pin in the pcm connector or the old one and just tap into the wire

Customer: replied 4 years ago.

I want to make sure we are on the same page. According to my Chilton wiring diagram, pin#59 (white wire) fires injectors 2,3,6,7. Pin# XXXXX (tan wire) fires injectors 1,4,5,8. I replaced injectors 2,3,6,7. Built new wiring harness from those injectors all the way to the ECU. I replaced the pin in the 60pin connector with another gold plated one out of a used connector. Tested the drag on the ECU pin prior to installing it. Everything is clean and tight. My new overlay also bypasses the engine compartment connection on the left fender. All my connection were soldiered and heat shrinked.

 

In short, not a new pin, but a good used pin with lead wire attached.

Expert:  Don replied 4 years ago.

Im sorry I was just using the numbers that way as an example your wiring is the same as mine. could you give me the vin # XXXXX I will call the ford tech line tomarrow and see if they have heard of this concern. 1234 are powered together but 2367 are grounded together

Customer: replied 4 years ago.

Cool, We are on the same page.

VIN# XXXXX

 

I REALLY appreciate your dilligence in this endeavour. It is just after 4:00 here. Time to start shutting down.

 

FYI: I am a one man operation here. So if some of my relpies are delayed, it's because I am also trying to get other work done at the same time.

 

Thanks!!!

Expert:  Don replied 4 years ago.
no problem willing to help in any way. I will call ford in the morning. I'm very intrested in what is causing this also.
Expert:  Don replied 4 years ago.

sorry it took so long to get back to you. here is the response from the tech line.

From the information listed suspect the vehicle is over 8500 GVW. As per the EVTM page 26-2 this vehicle uses bank fire when controlling the INJs on this engine. The INJs listed are grounded by the PCM pin 59. Please verify how the INJ pulse is being checked(noid light, test light, etc.). If there is a misfire issue present the PCM could stop INJ pulse. The PCM monitors the PIP signal from the distributer for INJ pulse. From the parts that have been replaced the concern is due to a PCM power/ground or an issue with the PIP signal to the PCM. Recommend to check the PIP signal to the PCM(using a DVOM, it should be half of battery voltage). If there is no issue present load test the PCM powers and grounds while performing a voltage drop. If the voltage drop is .2v or greater overlay the circuit being tested and re-pin at both connectors. Document if the vehicle is equipped with any aftermarket components(if equipped inspect the insulation of the components)

Customer: replied 4 years ago.

Testing for injector pulse is done with a noid light. On the good bank, noid light pulses get brighter and longer as expected. On the failing bank, noid light will start to brighten and then dim down to nothing. There are no aftermarket items on this truck. Even the stereo is factory. I will check powers and PIP signal again on Monday. Voltage drop of .2 would indicate that my grounds are all insufficient. Since my lowest one was pin # XXXXX was at .54.

Is there a common ground for the 4 grounds on the PCM? If not, where would I find them located.

Misfire... There is no noticable misfire occuring at idle.

 

Expert:  Don replied 4 years ago.
ok there are 2 grounds on on the passenger side up front, and on the drivers side back by the brake booster.
Customer: replied 4 years ago.

Here we go again. Just another manic Monday...

I serviced all the grounds. Grounds are good. Power supply is good. PIP voltage is 6.2 volts running. Just under 5 when I pull the spout.

Here is another question. The orange/red wire from distributor to pin# XXXXX what is it for? Taking a reading on that wire: key off = +.02, Key on = -.03, engine running = -.03.

I'm guessing it is the ground for the hall switch in the distributor. And is no help to solving this mystery.

 

I have no misfire until the injectors drop out.

 

I am about ready to invest in some C4...

Expert:  Don replied 4 years ago.
god I know the C4 option looks good. the orange and red wire is the ignition ground from the pcm
Customer: replied 4 years ago.

I am going to back burner this one for a while. I need to get some of the stacked up work done to pay some bills. Maybe try to get another truck like this one in here to compare things with.

 

If you get some other brain storm idea to try, just let me know.

Expert:  Don replied 4 years ago.
ok let me know if I can try to help any more
Customer: replied 4 years ago.

Hello Don,

I am finally getting back to this @$%# XXXXX

Just pulled KOEO codes for grins. I have: 654 - Manual Lever Position Sensor fault

558 - EGR Vacuum Regulator Circuit

624 - Electronic Pressure Control Circuit ( Transmision?)

Is it possible for any of these to affect injector pulse?

 

I also had a code 212 - no tach signal to processor. After running the test a second time, it did not return.

 

In the meantime, I am going to check every individual sensor to make sure none ore open or shorted.

 

Expert:  Don replied 4 years ago.
code 212 is for the cam sensor. this could cause the problems you are having. check the exciter wheel also for a crack or missing teeth
Customer: replied 4 years ago.

HI Don, During the past couple of months, I did get a Bronco in here with the same engine code. Swapped computers before the customer took it away from me. My computer worked perfectly in the Bronco. The Bronco computer had the same symtoms in my truck. Did not get a chance to perform any comparisons between the 2 trucks.

Ultimately, I jumpered the 2 injector circuits together and told the owner of the consequences and recommended to trade it off for a new truck. The beast still sits here, the company that owns it is on the fence in it's own future existence. They are not doing much business and may have to close up. They keep hanging on by a thread.

 

If anything changes or I get lucky, I will certainly let you know.

Brian

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