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Posted by: cal914 Mar 28 2017, 03:04 PM

Hi there

Just put our 1970 914 back to fuel injection from carbs and it purred for the first 30 minutes in slow moving traffic but then it began to cough and then was quickly nearly kangarooing down the street. It was fine idling but trying to pull away and driving it, it sounded as though it was misfiring or coughing or not running on all cylinders.

What's the checklist for trying to solve the problem?

Thanks!

Posted by: jcd914 Mar 28 2017, 03:15 PM

I would start with fuel pressure.

Posted by: zipedadoo Mar 28 2017, 03:34 PM

Check the throttle position sensor. Adjust, clean or rebuild.

Posted by: Dave_Darling Mar 28 2017, 07:14 PM

Ignition. Always start with ignition. Also make sure the basic engine is in good shape, valves adjusted and decent compression, etc.

--DD

Posted by: Jeffs9146 Mar 28 2017, 07:16 PM

If it starts and runs fine when it is cold then starts sputtering check the CHT sensor.

Posted by: mgphoto Mar 29 2017, 12:01 PM

Where there any mods to the engine, cam, displacement?

Posted by: cal914 Mar 29 2017, 01:12 PM

Took the car out again today,fine for the first 20mins then the problem returned.The engine has had no mods done to it and prior to fitting the Fuel Injection the car was running great
Thanks for any help that you can give

Posted by: Frankvw Mar 29 2017, 01:15 PM

Did you change the fuelpump from the low pressure carb pump back to a higher pressure FI fuel pump again ?

Posted by: boxsterfan Mar 29 2017, 01:25 PM

Sounds like CHT sensor.

Posted by: Rand Mar 29 2017, 01:26 PM

If it had a carb pump, would it run great for 20 minutes?

Have you checked the CHT as suggested yet?

Posted by: mepstein Mar 29 2017, 01:41 PM

Mine used to do that -intermitted bucking. I almost parted the car. I tried a bunch of things but I think it was just bad electrical connections.

Posted by: cal914 Mar 29 2017, 01:43 PM

Are the CHT sensor still available to buy new

Posted by: cal914 Mar 29 2017, 02:14 PM

Just found out The CHT censor was brand new out of a packet , that's one thing eliminated

Posted by: mepstein Mar 29 2017, 02:25 PM

I can't be sure but I think it was the wires around the tach and making sure the timing was correct that eliminated the bucking. I pulled off all the ground wires and cleaned them as well as the wires for the coil, ect.

I had done the chts but it didn't fix it.

Posted by: mgphoto Mar 29 2017, 02:39 PM

Are all the FI parts original and proper according to the rennlist site?

Posted by: cal914 Mar 29 2017, 03:16 PM

All the parts are original with NOS Bosch fuel injectors , we had 3 sets to choose from

Posted by: Jeff Bowlsby Mar 29 2017, 03:47 PM

There are several FI troubleshooting guides here:

http://bowlsby.net/914/Classic/TechNotebook.htm

And if you determine that you need a new harness...let me know.

Posted by: mgphoto Mar 29 2017, 04:07 PM

Your FI points in the distributor have grease on them.

Posted by: McMark Mar 29 2017, 04:18 PM

Did you take the fuel tank out? Pinched fuel lines underneath are a common problem.

Posted by: cal914 Mar 30 2017, 01:11 PM

Yes ,removed the tank and cleaned, the sock was all clear.On top of the ECU there's a grey knob that turns and clicks is there a best position for the knob to be to help with the running of the FI

Posted by: Dave_Darling Mar 30 2017, 02:00 PM

In the middle is the best position generally. Or, if there is a mark on the ring around the knob, any pointer on the knob should point to that mark. (That is evidently where it was set at the factory.)

Actually, the best position is the one that makes the idle nice for you at this exact moment, but that's not really what you were looking for...

--DD

Posted by: Jeffs9146 Mar 30 2017, 02:49 PM

The previous owner of my 74 had told me they replaced the CHT sensor so I tried everything else and nothing worked. I decided to check the CHT and it turned out that the PO had stripped the threads when he put it in so it was loose. When I fixed the threads everything started working great! Also check the wire leading to it!

Posted by: 914sgofast2 Mar 30 2017, 04:53 PM

I don't think you have the right ECU. Our early 1970 does not have a knob on the ECU. The adjusting knob was added to the ECU's on lster models so they could trim the idle & emissions. As suggeted above, please check the F.I. part numbers on the site Bowlsby suggested to make sure they are correct for your model year. For best performance, the distributor, the ECU and the MPS all need to be compatible with each other. Also check the Auxiliary Air Regulator ("AAR") to make certain it is functioning properly. If the AAR is not closing entirely when the motor warms up (i.e., after 15 or 20 minutes) it will put the engine in an excessively lean condition and act like a vacuum leak. You will spend many hours trying to find a mysterious vacuum leak, when it is the AAR that has gone bad. (Don't ask me how I know.) Our car ran fine when it was cold, but terrible once it warmed up becasue the AAR was bad.

Posted by: 76-914 Mar 30 2017, 05:30 PM

You won't know until you check the ohm values of the sender when hot & cold.

Posted by: pbanders Mar 30 2017, 10:07 PM

My web site (see sig) has detailed troubleshooting info for all D-Jetronic components.

Posted by: Mikey914 Mar 31 2017, 01:23 PM

Do check the cht, i have them if you need it, but id suspect its ok..
Does sound like fuel control

Posted by: injunmort Mar 31 2017, 06:03 PM

just something else to consider, the coil. when the coil starts to breakdown, they run fine cold, as they heat up, they expand and the windings separate, causing the condition you describe. try a coil swap and see if things change.

Posted by: cal914 Apr 2 2017, 03:01 PM

Changed the Relay board today ,Our very own MR 914 had a similar problem with one of his 914s and it turned out to be a connection in the back of the Relay board a connection that controlled the petrol pump.Going to take it on a long run tomorrow and see what happens ,I'll keep you posted with the results (fingers crossed )