1999 safari van

this van has 200,000 plus miles doen,t leak any fluids but it has a crusing speed miss, that sometimes seems to want to shut it down I have had it in several shops and a g m dealer ship, so far no one has been able to fix the problem ,it has had plugs,wires, mass air ,coils all changed at least twice, the fuel pressure is 50lbs when I bought the van it had 76 000 miles and it had a miss then and has continued to have the miss , I have not had the injectors replaced is there anything other than injectors that could cause this problem? at speeds of 65mph and aboveit miss,s badley.

The central fuel injection unit and ignition module top my list of strongest suspects for this issue, with the edge going to the ignition module. The part is pretty cheap, very likely to cause this problem, and no more difficult to replace than a distributor cap and rotor. Actually, if you have not replaced those items yet, it would be prudent to do so while you have them off to change the ignition module. Checking the central fuel injection unit is labor intensive as the upper plenum needs to be removed to access it, so I would suggest attacking the ignition module first. I’m surprised the person who changed the coil replaced that rather than the ignition module. Coils rarely fail while ignition module failures are relatively common (or at least common enough that I’ve replaced three or four of them compared to zero coils on these engines).

mark9207’s advice should be followed. I’ll just add some extra thoughts if it doesn’t go anywhere.

The engine’s compression should also be checked.

You said it had 50lb of fuel pressure. Do you know what the actual specs are? Was that a static reading? Someone should check it out under load.

Does that van have a tachometer? If so, what it the tach doing as it misses? Another thing those vans are known for is problems with torque converter clutch lockup due to valve body wear. A slipping TCC clutch apply can feel a lot like a miss.