96 LX450 - Intermittent No Start. Turns over but won't start

[goneballistic]

Our 96 LX450 is having this weird intermittent no start condition. normally it fires right up, but about 1 or 2 a week, it will turn over fine but won't start.

My wife will crank and crank and sometimes after a couple of minutes and several tries, it'll finally fire up. usually after it starts once, it'll be fine until the next time.


this morning it turned over and over and never would start. Not sure where to start looking.

I kind of assume the spark is OK since once it starts it runs fine and not rough or stumbling.


possible EFI Relay issue?

 

[goneballistic]

I am not feeling a click or anything in the DS fender EFI Relay when the wife powers up the system, I pulled that off and will look at that, i found a few threads talking about cleaning that relay up.

 

[excessive]

go thru this list
Emergency Troubleshooting Procedures - FAQ Item (Recommend Keeping Copy in Truck)

 

[85badger]

Check your coil wire

 

[RiverCityDave]

In my experience, the fusible link is the first place I'd start. Mine were bad but looked fine, causing the same intermittent no start. Basically the Ecu never received a "turn n" notice, even though the starter was spinning.

 

[jaymar]

Our 96 LX450 is having this weird intermittent no start condition. normally it fires right up, but about 1 or 2 a week, it will turn over fine but won't start.

My wife will crank and crank and sometimes after a couple of minutes and several tries, it'll finally fire up. usually after it starts once, it'll be fine until the next time.


this morning it turned over and over and never would start. Not sure where to start looking.

I kind of assume the spark is OK since once it starts it runs fine and not rough or stumbling.


possible EFI Relay issue?

Replace fusible link; fastest and cheapest thing it could be. $8 from CDan or beno. Fixed me right up. Until the starter went.

 

[goneballistic]

Ok I pulled the Fuel Pump Relay and cleaned it out, that didn't help. Still wouldn't start.

Then I decided that making as assumption about no spark was a bad idea. So I pulled the Cap and Rotor, just to look at them, and while they looked OK, they were kinda worn.

I threw another one on there anyway, just cause it's cheap to do it. This let the truck start, but it's still starting sort of slowly compared to what it used to do. I will order a new Fusible Link today and swap it out and see if that makes any difference.

At 220K miles, I'm sure they are not a bad thing to replace

 

[sbman]

Throwing parts can get expensive pretty quickly. The fact that it starts after replacing an item isn't a sure indicator that you have found the problem and can lead to invalid conclusions from faulty evidence.

A systematic approach is best. The FSM will have a troubleshooting flowchart for your specific issue (cranks but does not start). You go through the flowchart one by one until you find the problem. It's much easier to diagnose it while it is exhibiting the symptom than when it is intermittent. The basic steps area the same for all vehicles, although it is more difficult the newer the vehicle is (COP systems for instance make it harder to check for spark)

The easiest way to check for spark on the 80 and most older vehicles is to use an old spark plug and wire. then you can simply disconnect one line on the distributor cap and hook up your old spare wire/plug, set it on something metal and crank away. That does not guarantee you have GOOD spark going on inside the engine, but it does verify that the computer is functional, coil is functional, distributor/rotor is functional. It is possible to have a weak coil that will produce a spark in open air, but isn't providing enough voltage to produce a spark in the combustion chamber at increased pressures (it is harder to make a spark in compressed gasses than it is at atmospheric pressures). You can test the wires with a multimeter and inspect the spark plugs for issues to be thorough. Look for cracked or burnt insulators on the spark plugs. If you drop a plug, consider it dead and replace it because the ceramic insulators are very brittle and can be cracked easily. All of these steps are outlined in the FSM troubleshooting flowchart.

Next up is fuel. On many vehicles this is as simple as hooking up a fuel pressure gauge to the service port on the fuel rail. Mr. T decided not to give us one of those, so there is no easy way to check for fuel. The FSM has you disconnecting fuel lines and removing seats because that's the only 100% certain way to do it, so you have to go down that path to ensure you have fuel.

With spark and fuel, if you still aren't starting you start to get into more onerous problems like lack of compression and a compression check is in order.