'94 Volvo 850 sedan, automatic transmission, not a turbo

The car cranks properly but the engine will not start. Dashboard lights appear normal while the starter motor turns.

While troubleshooting I discovered the engine coolant temperature sensor had failed and replaced it.

Here's the current problem: when using the diagnostic port, there is no LED response from A2 (MFI) and A6 (fuel) when I push the button for a second. Also no response when I hold the button for 6 seconds, the start of the process to clear the codes. The LED lights whenever the button is pressed but there is no answering LED activity from A2 and A6. The LED acts normally for other ports, including the transmission.

I have verified electrical continuity between A2/A6 and the B5 pin on the MFI and fuel computer boxes. I have verified that the main engine relay works.

Can someone please tell me which are the power pins on the fuel & engine computers so I can verify that they are getting power?

Any other troubleshooting ideas? At this point the Volvo diagnostic manual says I should try swapping in new engine and fuel computers. But gosh, I just don't have spares.

Thanks for the help.

My 850 wouldn't start for a year. Cranks but will not run. I re-registered it and was about to have it towed to Volvo. It was in my garage at the top of a steep driveway. I rolled it down - popped the clutch and it started and has run great for the subsequent 6 years. I'm assuming some air something was stuck open letting to much air in. I drove it straight to Volvo but they had no answer.

Are the doors closed? I puzzled for a while with that trick :) seems that the DTC modules don't like the open circuit of the doors.

Are any of the plugs wet after a start attempt? Has this engine been run recently? You could try a small amount of engine oil in each cylinder, one of the BB's used a drinking straw with about 2 inches of oil in it to get the oil down to the piston. Car started nicely with better compression.

Klaus
--
Proud owner of a 1967 220S

Get back to basics and find out WHY it wont start!
For an engine to run you need 3 things
fuel
spark
compression

and air but that you can take for granted

1. check to see if the fuel pump is running, turn key to II position you pump should run for a few seconds..if you cant nor have ever heard it before. get someone else to turn the key while you have a listen thru the gas cap (remove the gas cap)

2. check for fuel pressure at the fuel rail remove the cap off of the shrader valve at the end of fuel rail near the throtle body and press the pin..gas should pour out..be carefull

if no fuel activity on either above suspect is the pump itself or the fuel pump relay and camshaft position sensor oh and course fuel pump fuse!

then check for spark..easy way is to remove one spark plug keep it plugged to the lead ground the plug and watch for spark while someone else cranks it! if yes good..

and report your findings