BLDTruth

Drove my truck down to pickup a pizza today - when I got back into it and started it, it was a little reluctant to start but fired up. Noticed my idle was higher than usual by about 300 rpm, and when I put the clutch in to put it into neutral, it would hover around 1500 rpms and not really drop until I came to a stop. Got home and left it for a bit, came back out and she fired back up again but still had the weird idle problem. Took it for a spin and it drove pretty normally. Got it home and turned it off - went to fire it up again a few seconds later and it tried to start before completely falling on its face and cutting off. Now it won't even try to turn over. Swapped the coil and ICM with no luck (had working spares). Friend came over and I can see I have good spark at the coil, just won't turn over. Cranks all day. Spark at the coil should mean the PIP and ICM is functioning, if I recall correctly.

I'm going to get my fuel pressure gauge back from my buddy tomorrow but it does it on both tanks, and I would imagine if it were fuel related it would at least attempt to crank over. But I'll take all thoughts from anyone willing to give them. When I saw the weird idle I thought maybe the TPS or the IAC was shot. TPS has been replaced in the last few years, IAC has never been touched but would a clogged IAC prevent the truck from starting altogether?

Thanks in advance. Just looking for a starting point, or someone to point out the obvious thing I am not thinking of.

SaltEater

Afaik the IAC is full open when starting and then 'flutters' during idle. Will it start if you hold the throttle open a little?

High idle would suggest an air problem over a fuel one right?

Steve83

Your description isn't really clear... Is the engine spinning & not firing? Or is the starter not spinning the engine? If it's the latter, you should read all the captions in this photo album & then check your truck:


(phone app link)

BLDTruth

Sorry for the stream of consciousness.

When I say crank but no start, I mean the starter is engaging but it will never turn over and run. It reminds me of when I had a bad PIP, but when I had a bad PIP, there was no spark at the coil. Here I have spark at the coil. Fuel pumps are priming so I know the relay and the intertia switch are good. I guess I just need to follow the spark to the plugs and measure fuel pressure to be sure that isn't it.

Steve83

It takes 5 things for an engine to run:
1) air
2) fuel
3) compression
4) ignition
...all at the right...
5) time.

Make sure you check each one, although you can assume it's getting air if it passes the compression test.


(phone app link)

This caption contains the complete test for that ignition:


(phone app link)

BLDTruth

Another buddy suggested this as well - tried holding the pedal down a bit and no luck with starting.

Tomorrow i will go over everything obvious and hopefully its something simple

wde3477

Suggest verifying spark at the plug, as well as checking out the IAC for crud / sticking are good steps.

When you're cranking over and over, do you ever smell fuel? Kind of a reach, wondering if something is going on with the fuel injector system? There were a couple of threads on here about some common ground for the injectors possibly being an issue.

BLDTruth

If the IAC is bad I should be able to unplug it and then the truck would start, correct?

I'll check the fuel pressure today and see if the regulator line smells like gas. The more I have read last night the more I am thinking the timing chain may have jumped. The first time it started with the idle problem it kind of clunked a little bit and fell on its face before firing up and running. When I got home and turned it off and then tried to turn it back on again, it sounded like it wanted to go for a minute and then just died. Now it won't even think about starting. I wonder if it slipped the first time just enough to let her keep running, the second time was the end. Timing chain has never been changed and truck has 205K miles on her.

So what's my best bet for checking timing without a running truck and a timing light?

Cap and rotor are basically brand new but I will verify spark all the way to the plug. Once the sun comes up haha.

wde3477

Eh, dunno if unplugging the IAC will tell you anything, given what you've already tried, but no harm in trying.

Easiest way I can think of to quick-check the timing is to roll the motor around to its 10BTDC timing mark, then pop the distributor cap. The rotor should be at the #1 post or exactly 180 degrees out - depending on whether the cylinder is at the top of its compression cycle or exhaust cycle.

Typically, I've experienced than when timing jumps, the engine has an unusual lope or cadence that ain't quite right when cranking. Also, if there was a jump, would still expect some misfiring/farting and backfiring if spark and fuel are still present...unless the chain flat broke.

FWIW, when I changed my chain at about 170K, it had a little over an inch side-to-side play, where the manual recommended no more than 3/4-inch. Still ran fine, though.

BLDTruth

Alrighty here's an update:

Went out this morning and she fired right up....one crank then vroom. Let her sit for a minute and she idled down but still sat higher than she normally does. Turned it off because I had to run a friend to work in my other car.

Got home, she fired up again right away. Took her out for a spin around the block and let her get up to temperature. Drives fine so the timing chain is out as a possibility I think. Idle is still weird, hovering around 1000-1200 rpms. If I'm cruising at say 40-50mph and I put the clutch in, the rpms stay at around 1800-2000 rpms until I get down to a lower speed and then it will eventually drop to 1000-1200rpms.

Got back home from the drive and turned her off. Went to turn her back on and it did the exact same thing it did yesterday - tried to start and then a little rumble noise and then nothing. Now it just cranks and cranks again with no start.

So now I am thinking it could be something related to a warm start problem. Which makes me think sensors. Any thoughts?