1994 850 no start: fuel, spark, but no injector pulse

mtoups · Post by **mtoups** » 02 Dec 2013, 09:10

Hello friends. My 850 (non-turbo) won't start. It was intermittent for a short time and now is consistent, has not started for weeks.

Fuel pressure to the rail is good. Spark plugs are firing. Compression is good.

No injector pulse!

Port A2 is dim so I can't read any codes.

I replaced:
* Fuel injector relay
* Fuel pump relay
* cam position sensor
* crank sensor
* two ECUs (cp02 6.2) and (cp01 5.1 - ignition)

Still no start. Checked lots of wires, found no problems. Battery voltage looks good. Any suggestions?

What other component could prevent injector pulse but still give me spark?

Thank you for your advice!

Post by **jblackburn** » 02 Dec 2013, 09:13

Test battery voltage to the fuse box/relay panel and see if it is getting a proper signal. Also check grounds in/around the battery area, incl. the one at the back of the cylinder head and under the car.

Post by **misha** » 03 Dec 2013, 02:54

Master fuel injection relay.It's the big grey one and it's located at the top of the cooling fan carrier.
Usually...it's stamped Made In Hungary on it.

Post by **erikv11** » 03 Dec 2013, 08:17

OP already replaced that relay, see the first post. But it would be worth looking carefully at the wiring on the plug there.

socompsp · Post by **socompsp** » 03 Dec 2013, 12:58

double check the connections to both the cam and crank sensors. the plastic connectors on the ecu end get corroded. were the sensors new? what does the ecu main connector look like? how are you sure there's no inj pulse? also maybe try starting with MAF unplugged.

Post by **northernlights** » 03 Dec 2013, 18:42

mtoups wrote:Hello friends. My 850 (non-turbo) won't start. It was intermittent for a short time and now is consistent, has not started for weeks.

Fuel pressure to the rail is good. Spark plugs are firing. Compression is good.

No injector pulse!

Port A2 is dim so I can't read any codes.

I replaced:
* Fuel injector relay
* Fuel pump relay
* cam position sensor
* crank sensor
* two ECUs (cp02 6.2) and (cp01 5.1 - ignition)

Still no start. Checked lots of wires, found no problems. Battery voltage looks good. Any suggestions?

What other component could prevent injector pulse but still give me spark?

Thank you for your advice!

Whenever strange starting problems occur as the weather gets colder, I like to look at the coolant temperature sensor. A bad sensor can really mess up cold starts, much like a non-functioning choke used to in the days of carburetion.

When you say you have no injector pulse, how did you check that? The injector should be always be hot on the 12V side once the engine decides to start. If you don't ever have 12V to the injectors, then the car isn't ready to start, and you need to look again at the upstream checks the system does prior to starting, i.e. the cam and crank sensors. If the ECU doesn't know for certain that it is turning it will not fire the injectors.

Here's what the system looks for:

FUEL INJECTION

As the engine is turned by the starter motor, the Engine Speed sensor (7/25) and Camshaft Position sensor (7/21) deliver engine speed and crankshaft position signals to the ECM, which opens the injectors once per working cycle to inject fuel.

One terminal of each injector connector is supplied with 12 Volts from the main relay, while the second is connected to the ECM, which operates the injectors by grounding the appropriate lead.

During the start-up phase, the ECM computes the injection period on the basis of the engine temperature and speed signals.

When the engine is running, the injection period is based on the engine speed, temperature and load, battery voltage, and other parameters.

socompsp · Post by **socompsp** » 03 Dec 2013, 21:49

just to add a side note, you can check the fuel pressure at the rail with a tire pressure gauge. but dont use your main one, the gas will ruin it. spray some starting fluid in the intake and see if you get a pop.

mtoups · Post by **mtoups** » 30 May 2014, 21:33

jblackburn wrote:Test battery voltage to the fuse box/relay panel and see if it is getting a proper signal. Also check grounds in/around the battery area, incl. the one at the back of the cylinder head and under the car.

this turned out to be the issue: grounds

Unfortunately the grounds I could access seemed fine. My mechanic eventually found the bad grounds to the ECU, located in hard to reach places like behind the starter. Rather than re-run wires to those places, which would require taking apart the intake manifold and other things to reach it, he ran a new ground to the frame right in front of the battery. Now the car starts/runs fine.

A lot of trouble caused by some bad wires!

jamesL850 · Post by **jamesL850** » 31 May 2014, 01:59

Hi. I recently serviced (ie replaced) the pcv system, removing the inlet manifold. And most of the protective (plastic) shielding around the wires was brittle and crumbly - perfectly understandable your situation of having a bad earth. I found two earth wires just above the starter and I think there may have been another below too. Oil, gunk, heat and time ... On top of my motor the injector harness protection was crumbly too - my fix ?? I used gardening piping - the black tubing buried with the push in sprinklers. Thickly walled thus more durable than stock protection, just required an end to end slice. Then electrical taped the entire length, all the way to where it meets the hard shell covering underneath the airbox on top of the gearbox.