4.6L won’t start
Thread Starter
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Member
Joined: Jan 2004
Posts: 24
Likes: 0
From: Flower Mound, TX
4.6L won’t start
Ok, this is an exhaustive post, but I’m at my wits end.
I have a 99 Expy 4.6L. One morning it ran me to work. The engine ran a little rough, but no CEL came on. That afternoon the engine would only crank but never start. In the parking lot I listened for the fuel pump to come on (it seemed fine). I hit the pressure valve on the injector rail and gas squirted out. I took out the #1 plug, grounded it, and watched it spark. I sprayed throttle body cleaner down the TB, but the engine wouldn’t start. I even unplugged the battery for a couple of hours to try to reset the PCM.
The next day I replaced the fuel filter, all the plugs, all the plug wires (no chance of cross-wiring), the air filter, and the fuel pump relay. I could get the engine to run for only a second when I sprayed TB cleaner in it, but it wouldn’t keep running. I also added fuel treatment to the gas tank to remove water, just in case.
The next day I checked the resistance across all the injectors without any problems noted. I checked the resistance across the crankshaft and camshaft sensors and they were fine. I tried to check voltage to the same sensors with no luck (I also tried to check the voltage on my 99 F-150 with the same setup and no luck, so I attribute this to operator failure, not parts failure). I checked the power to the coils and that seemed fine and so did the primary resistance. I tried to check the secondary resistance across the coils with the same results as the CKP and CMP sensors (again compared to the working F-150). I then used an induction timing light to see if all the plugs were getting spark and only 4 were. I thought it was a bad coil, except that 3 of the non-firing plugs were from one bank and 1 was from the other. It was then that I noticed the driver’s side coil had a crack. I replaced the coil, but the engine still won’t start. I am trying to figure out the best way to check the wiring between the sensors and PCM and back to the ignition coils. Any help there?
I replaced the IAC about 6 months ago and I’ve checked all the fuses. Based on the hundred or so threads I’ve read today I’m going to try to clean the MAF, check the vac hose between the PCV and idle control valve, and pull the IAC off and look closely at it. In addition to this, does anyone out there have any suggestions?
Again, sorry for the long post, but it’s been a long few days. Thanks.
I have a 99 Expy 4.6L. One morning it ran me to work. The engine ran a little rough, but no CEL came on. That afternoon the engine would only crank but never start. In the parking lot I listened for the fuel pump to come on (it seemed fine). I hit the pressure valve on the injector rail and gas squirted out. I took out the #1 plug, grounded it, and watched it spark. I sprayed throttle body cleaner down the TB, but the engine wouldn’t start. I even unplugged the battery for a couple of hours to try to reset the PCM.
The next day I replaced the fuel filter, all the plugs, all the plug wires (no chance of cross-wiring), the air filter, and the fuel pump relay. I could get the engine to run for only a second when I sprayed TB cleaner in it, but it wouldn’t keep running. I also added fuel treatment to the gas tank to remove water, just in case.
The next day I checked the resistance across all the injectors without any problems noted. I checked the resistance across the crankshaft and camshaft sensors and they were fine. I tried to check voltage to the same sensors with no luck (I also tried to check the voltage on my 99 F-150 with the same setup and no luck, so I attribute this to operator failure, not parts failure). I checked the power to the coils and that seemed fine and so did the primary resistance. I tried to check the secondary resistance across the coils with the same results as the CKP and CMP sensors (again compared to the working F-150). I then used an induction timing light to see if all the plugs were getting spark and only 4 were. I thought it was a bad coil, except that 3 of the non-firing plugs were from one bank and 1 was from the other. It was then that I noticed the driver’s side coil had a crack. I replaced the coil, but the engine still won’t start. I am trying to figure out the best way to check the wiring between the sensors and PCM and back to the ignition coils. Any help there?
I replaced the IAC about 6 months ago and I’ve checked all the fuses. Based on the hundred or so threads I’ve read today I’m going to try to clean the MAF, check the vac hose between the PCV and idle control valve, and pull the IAC off and look closely at it. In addition to this, does anyone out there have any suggestions?
Again, sorry for the long post, but it’s been a long few days. Thanks.
Thread Starter
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Member
Joined: Jan 2004
Posts: 24
Likes: 0
From: Flower Mound, TX
Well, I spent the better part of a week checking just about everything. I say "just about" because I towed it to a shop the other day and they came back and said that 2 cylinders have zero compression and 1 cylinder has 50% compression. The others checked out OK. They were still stumped as to why the engine didn't want to at least run rough vs. no start at all. Now I'm debating on throwing in apprx. 4 grand for an engine (w/ labor) or purchasing a new truck. The shop said they would tear the engine apart, but that with labor and incidentals, it would be within a couple of hundred of a new engine (that comes with a warranty). Tough spot....
Oh well, such is the life of Fishbrains.
Oh well, such is the life of Fishbrains.