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93 Suburban, back fires, starts and 100 rpms than goes to 1000.

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Hello everyone,


I've been messing with my 93 Suburban for the past 2 days and I just can't pin point where the problem is.


1993 Chevrolet Suburban

7.4L 454 BB





On Saturday it wouldn't start so I took a look and found out that the injectors weren't working so I took out the ICM and had it tested, they said it was fine so I went back home and put it back in and than the injectors worked but than it would die.


I went back over every wire and hose I messed with until finally it would stay at the point of idling but only at about 100 or 200 RPMs it would backfire but run, when I gave it gas it would shake like an earth quake was going on until it hit 3000 or more RPMs it would be fine but have some backfires.


While it was running I jiggled more wires and now it will idle at 100 rpms and than a couple of seconds later it will jump up to 1100 rpms and than die back down to 100 rpms, it will keep doing this until I turn it off. I thought I found the problem when I jiggled the 2 pronged wire coming from the coil to the ICM but it's hard to say since it dies and picks back up randomly, I started it this afternoon and it ran fine for a couple of minutes and than it went down to 100 rpms and stayed there and than it will fluctuate, for as long as I've had it I have had to hold my foot on the gas a little to be able to start it, it wouldn't start on it's own unless it was warmed up.


I have already checked when I was trying to figure out the injector part, the fuel pump and fuel filter "those were both changed a year ago" tested the ICM 5 times. Distributor cap and rotor could use replacing but I took some 1000 grit sand paper to the points and cleaned out the cap and cleaned off the rotor, spark plugs and wires were replaced the same time the fuel pump and filter were changed. I went back to make sure all the wires were in the right location and to make sure the wires were plugged in nice and tight as well the wires for the ICM and anything else I touched.

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Sounds like you might have multiple problems.Rather than throw a bunch of parts & money at it I'd consider taking it to a dealer and have them put their scanners on it.It can be easy to replace several parts & not solve the problem.Hopefully you have an honest dealer nearby.

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I have it working now, the pick up coil plastic that was covering the wires crumbled in my hands when I first took it off so plugging it back in I guess they didn't connect right so I took off the plastic piece and put the wires in the right spot and runs like a dream


Thanks for the suggestion grampadirt.

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