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injector pulse problem

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Old 12-12-2010, 04:53 AM   #1
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any body please advise possible cause of the following problem:
from time to time it happens that my jeep cherokee 1990 4.o l have no injector pulse , spark is ok , fuel pump is ok , but when i unplug and replug these four relays near the battery ( latch and fuel pump and oxygen heater relays ) the injector pulse is ok and the car starts .is it a problem of bad ground ?
please if any body faced similar problem give an advise.

Thanks
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Old 12-12-2010, 06:23 AM   #2
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Have you tried changing the relays yet maybe one is bad
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Old 12-12-2010, 09:08 AM   #3
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I had a similar issue, and finally loacted the problem by accident, the main injector pulse wire going to the injectors had broken, the break was located where the main harness running from the injectors going back to the firewall then bending up and back over to the main fusebox (autoshut down relay) while performing a volt check of the injectors I had moved the wiring harness and I got good voltage, after undoing all the heat shrink I found the break. I respliced the main wire, and I was G2G
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Old 12-13-2010, 12:20 AM   #4
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Hi Messrs Freegdr , CJ7365
Thanks for your advices , and at the weekend i will do what you suggested .

Thanks and best regards
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Old 12-13-2010, 05:57 AM   #5
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Grounds can be the root cause of many electrical gremlins. (especially on RENIX vintage which is 87-90) Refreshing grounds is NEVER a bad idea!

You can't just check or look at these grounds. You must remove, scrape, clean until shiny the cable/wire ends and whatever they bolt to. The one on the back corner of the head, and where it attaches to the firewall. Scrape the paint from the firewall. Best to replace that woven cable with a #4 or #2 gauge cable. You can attach the one end to the intake manifold if you would like.

Next go over to the engine dipstick tube stud. Remove the nut and clean the wire ends and scrape the block until shiny at the stud. Reattach tightly.

If you are so inclined, add at least a #6 cable from the negative terminal of your battery to one of the bolts on your radiator support. Scrape the paint off first.
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