Joshua Fazekas

Hey guys. I purchased a 86 951 a year ago. I've slowly been fixing things as i go. One issue I can't seem to figure out is the car randomly doesn't start. After waiting about ten minutes of trying the car fires up with no issues. It always seems to be a humid day when it happens. I've replaced the fuel relay, plugs, rotor and cap, fuel filter. The car still does it. It can be really frustrating when it happens. If anyone could provide some help I would greatly appreciate it! Thanks much in advance!

Josh

fejjj

I would try replacing the DME relay.

I had a similar problem and determined that the relay was dying a slow death.

Auto_Werks 3.6

Could be a lot of different things. Sounds like you replaced the DME relay when you replaced the "Fuel Relay". When the car is acting up try to verify whether the fuel pump is actually running. Also, does the tach bounce when it's cranking? Wires in these cars are getting old, possibly the speed and reference sensor wiring is on its way out... Also failing DME and KLR units can have some strange no start symptoms too.

bajabluejay

Speed/Ref Sensors as Werks said. Next time you get a no-start, pop the hood and poke the sensors with a stick. Try again. Always works

Pull the vac lines on the fuel damper and regulator on the fuel rail when the car is running. Do you see fuel coming out of the vac nipples? If so, that's bad and they should be replaced. I've known a failed damper to cause a no-start before.

mikec944

A failing factory alarm module will cause the car to intermittently not start. It is very easy to bypass and even if it is not your problem now, it will be a problem in the future. It is a good preventative measure for a no start condition.

Bypass directions: http://www.clarks-garage.com/shop-manual/elect-23.htm

Joshua Fazekas

Yes I replaced the dme relay. Sorry it was late last night and I was blanking on the name of it lol. Thanks for all the suggestions I will look into it and keep you guys updated! When I do try and start it the tach does bounce and shows 1 bar of pressure on the factory boost gauge.

Tom M'Guinn

Happy to see the 1 bar test filtering into the world With bounce and 1 bar on the gauge, the DME relay and speed and ref sensor wiring is "probably" ok. Check for fuel and spark -- that will help point you where to look. If you have spark, but no fuel, you might check the injector wiring. It frays inside just like the speed/ref sensors, and one shorted injector will keep them all from firing -- fairly common on these cars. Cracked DME/KLR solder joints (or worse), alarm, ignition switch, bad ignition parts, are also possibilities...

raleighBahn

Another quick/easy test from Clarks is unplugging one of the injectors and then trying to start. The FPR can fail in such a way that there is crazy pressure on the rail, preventing ignition.

But if you have fuel pressure gauge, as Tom said, you can run it down. Check pressure on the rail (before and after starting, ie jump the fuel pressure/dme relay), check the fuel pressure leakdown time, check spark, check voltage and resistance of the ignition coil, etc.

cruise98

Check the fuel pump. A fellow Rennlister has had 3 or 4 brand new pumps that were bad within a week or so out of a Bosch box. Not sure if they were just well concealed Chinese knock offs or not. There was also a bad batch of DME relays from Hungary. Just because it is new does not necessarily mean it is good.

Joshua Fazekas

Sorry for my lack of knowledge but how would I go about testing the fuel pump? I'll have to see where my dme relay came from. I bought it from pelican parts.

Joshua Fazekas

I'm also wondering if it's my alternator. I don't think it's charging my battery. I just put a brand new battery in like two months ago and it went from 14 on the battery gauge and sits around 12. Doesn't the car require 12.6 volts to start?

So many things to troubleshoot. What have I gotten myself into with this car?!

Humboldtgrin

Ever try testing out the ignition switch?

eurojulien

does your rpm needle bounce a bit when it doesn't fire? If not it's probably the reference sensors

Joshua Fazekas

Yes it does

Joshua Fazekas

No I have not