erratic injector pulse?
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erratic injector pulse?
I have a 1988 f150 5.0 efi truck... When I got it, I replaced all fuel pumps, complete tune up, and went through the intake gaskets...it ran phenomenal... Now, it has an idle and drivability issue... You can hear it in the injector pulse pattern... It will idle ok for a few minutes then try and stall out... Injectors start firing out of sequence or rapidly/erratically... What controls the injection signals? Ignition system doesn't seem to miss a beat... When the injectors start firing erratically, it seems the ignition system misses as well... Not certain... As long as I keep the rpms up, it stays running... But tries to fall on it's face... Any suggestions?
Fleet Mechanic
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From: Saskatchewan Canada
I would be quite interested to know how you determined the injector pulse is erratic and how you follow the "injector pulse pattern"?
Have you verified fuel pressure with a gauge and are there any codes set.
The injectors are controlled by the EECIV ECM, which in turn requires specific inputs.
Your truck is very likely speed density with batch fire injectors. That means banks of 4 injectors fire alternately, not individual injectors sequentially.
Have you verified fuel pressure with a gauge and are there any codes set.
The injectors are controlled by the EECIV ECM, which in turn requires specific inputs.
Your truck is very likely speed density with batch fire injectors. That means banks of 4 injectors fire alternately, not individual injectors sequentially.
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While the truck idles... You can hear a light tick sound, almost like a spark... Just about any efi 5.0 I have been around does it.. The mechanical sound of the injectors. Now, the problem is intermitent which makes it hard to track the problem... It has not thrown any codes or an engine light... I have looked for loose or bad wiring and Inspected ignition components... I will put a fuel pressure gauge on it tomorrow... But it doesn't run like a fuel pressure issue... When it starts the erratic injector tick, it still readily revs up to 4500 rpm easily... But with a studder... Or slight stumble... It doesn't really break up... Thus why I am confused... I have always been a mechanic... And usually have no problem repairing my issues... But chasing this gremlin is bugging me... Could there be a bad injection signal or the ecm shorting out?
Last edited by jonpdubois; Feb 11, 2017 at 07:44 PM. Reason: extra question
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Have you actually checked for codes? Or are you just assuming there are none because the check engine light isn't on?
All the timing information for firing the injectors comes from the ignition system - specifically through the TFI module, through the PIP sensor.
All the timing information for firing the injectors comes from the ignition system - specifically through the TFI module, through the PIP sensor.
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From: Saskatchewan Canada
If you are hearing injector tick, you have better hearing than me. Not really a surprise because I am a bit of a fossil.
Still, if you have an audible change, maybe you have a sticking injector? I really don't think you are going to find an electrical cause. Keep in mind your bank fire injection has only two distinct signals, (supplied ground), and fires 4 injectors on each bank. Maybe this can be isolated best with a stethoscope? Sticking injector would not directly set a code, although if it runs poorly, I would suspect you would eventually get some O2 sensor codes.
Still, if you have an audible change, maybe you have a sticking injector? I really don't think you are going to find an electrical cause. Keep in mind your bank fire injection has only two distinct signals, (supplied ground), and fires 4 injectors on each bank. Maybe this can be isolated best with a stethoscope? Sticking injector would not directly set a code, although if it runs poorly, I would suspect you would eventually get some O2 sensor codes.
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This truck would be considered obd1... Which I am not very familiar with... My mechanics class instructor didn't really push on obd1 because it was being phased out for obd2... I have not actually checked it for codes... Is there a "flash" mode for activating the engine light to show a code? How is it done?
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From: Saskatchewan Canada
Yes, that is correct.
Likely because the EECIV ECM has been phased out for over 20 years. Hard for an old geezer like me to believe!
And now we need to do this.
First, maybe a mod could fix the link for code retrieval in the stickies?
Lacking our very own sticky, you are going to need the instructions to enter "self test", (no flashing ECM's of this vintage), and a list of codes. Here are a couple I found with a Google search.
http://www.tomco-inc.com/Tech_Tips/ttt6.pdf
EEC IV 2 digit codes
EEC IV 3 digit codes
First, maybe a mod could fix the link for code retrieval in the stickies?
Lacking our very own sticky, you are going to need the instructions to enter "self test", (no flashing ECM's of this vintage), and a list of codes. Here are a couple I found with a Google search.
http://www.tomco-inc.com/Tech_Tips/ttt6.pdf
EEC IV 2 digit codes
EEC IV 3 digit codes
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fordman1954
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