l have recently put brand new glow-plugs on my 99 ford econoline diesel van 7.3 motor and l am having lots of problems now the van will turn on only when it wants whether it is cold or sunny outside ...what can the problem be?

Had same motor and year but on truck. If they came with seals they have to be set correctly. My problem was dirty fuel filter and the fuel would drain back to tank leaving most of line dry.

Was this happening prior to the glow plugs being replaced? If so, GP is were not the problem. If this has happened recently after the GP is were replaced, maybe someone made a mistake somewhere?

If u have a code reader, best thing to do is check for error codes. A computerized engine can be very picky. And the way u r describing it, it could be random.. It sounds like it is electrical though.. but not related to the GP system- maybe the injection system.

So this happens after u say, drive it to XX location & the diesel is nice & warm. You park it & come back, no start- sometimes. A warm diesel usually will start quite easily. If it is hard to start for the ''first'' start of the day AND after the engine has sat a LONG time to cool off.. it could be GP related. l hope u bought OEM Motorcraft glow plugs. They're the best from what I've heard (there is one other brand that is good). The rest tend not to last that long..

l have heard of the injection drive modal (aka computer- another one) going out. But l am not sure it could be the issue. It tells the fuel system when to ''fire''. You did not pressure wash under the hood did you? The unit is usually mounted on the inner driver side fender.

Check the plug harnesses for all connections under the hood. It is possible that something might have been put together loose under the hood...

Search the website in sources. The dieselstop is a Ford diesel site.. covers all diesels used in Fords. from the 6.9L to the 6.6L I-6 used in the 1990 is in the F550 is to the new 6.4L

A little more info is needed to help guess what the problem could be.