Looking for input. I've had my 89 van with a 4.9 in the shop twice with no success. It has a miss when it warms up, first time shop said it was a faulty temp sensor. They changed it and no change. I put new plugs, wires, cap and rotor, had a starting problem so I replaced ignition control, idle control and throttle position sensor. Still has issues so I took it back into the shop and they said the intake plenum was carboned up, so they say they cleaned it. As soon as I left the shop and the vehicle got warm it started to miss again. If anyone has advice or suggestions I'm up for input Thanks.

 

Have you had the computer scanned for hidden/stored codes? It can be your best friend. Most automotive stores will scan it for no charge.

 

If it's an intermittent miss, I'd be looking at fuel delivery. I had to re-tune my Carter carburetor because my motor was getting a lean pop in the exhaust.

If it's a consistent miss, I'd be looking at the mechanical parts or the ignition components. Bad valves, head gaskets, warped manifolds, distributor, ignition module, coil, etc.

Like 86F150six says, get the codes and see what she says.

 

To me that sounds like a vacuum leak. Take a can of carburetor cleaner and spray it around the various vacuum connections and gaskets on the motor, if you spray one spot and the motors runs smoother, you've got a leak.

Brake booster can cause a big leak, I just replaced one on a friend's truck that had a similar issue. To test it pinch off the big vacuum line that feeds it with a pair of pliers and see if it gets better/worse, either way, you have a vacuum leak.

Also, does the van warm up quickly and the heater blow nice and hot? Or does it take forever and not get all that hot? The thermostat can also cause running issues. They're cheap ($10) so I'd just go ahead and replace it with a new one (192 or 195 degree only)

You might want to try another shop, they don't sound like they really know what they're doing...

I hope you get it figured out!

Sam

 

x2 ... sounds like they are flailing around in the dark . they can find your wallet alright, but nothing else.

 

Ummmm...........

The 4.9's are VERY sensitive to poor grounds.

A lean stumble (if that's what you consider a "miss") CAN be caused from poor grounds in the ignition system.
That would include the negative battery cable at the battery, frame ground, and the block ground (should be at the starter).

Clean those grounds (wire brush 'em) and drive your rig around a bit to allow the computer to re-learn itself.

I agree that your mechanics are "flailing around in the dark" on this one.

Just my thoughts.

Bob

 

You all hit a good point about the garage, which is why I decided to post here and not return there. I'll try to hit some of the points addressed. The van is an 89 fuel injected but I'm not sure how advanced of a computer it has as far as giving codes, there is no check engine light. I spoke with a friend yesterday and we were thinking maybe a coil issue due to the probem only arising after warm up. It has the original coil with 103000 (original) miles on the engine. When I first started to diagnose I did check the vacuum and spry around lines and the base of the intake, I did not however check the brake booster. I replaced the water pump last weekend to add to everything I started it up and it dumped anti-freeze on the ground and turns out the bearing was shot in the water pump, with that said it got a new thermostat and a radiator cap. I will also give the ground another check I have traced those line down to the engine but another check might find something. On the line of the ground, I have a very sticky ignition switch meaning it turns extremely hard, so much that on these cold WI mornings I have to use a pliers to completely turn the key to start, and then physically return the switch back to nuetral, could this be something that would affect ignition ground? Thanks for all the imput, any other suggestions send them my way.

 

Just as another note:

A poor ground(s) can manifest itself to appear as a "bad coil" within the ignition system.

If the ground circuit going back to the battery negative post is too resistive, the coil will appear to be failing.
You need to have a nearly perfect (think direct) ground from the block to the negative battery post, else there will be too much resistance for the coil to function correctly.
That CAN cause a lean stumble........especially at low RPM's.

Hope this helps.

Bob

P.S. Wow, you've got an ignition switch/tumbler problem that should be addressed right away before it leaves you stranded.