Amirthe1

Hello everyone, I am having a very strange problem with my 1986 951. It starts right up however the idle is quite rough and the rpms are not steady. Also, when I give it throttle (regardless of the amount) it does not go past ~2500rpm, it just bounces as if it were hitting a rev limiter. I bought this car a while back in a non-running condition, which ended up needing a new fuse box as it wasn't getting power to the fuel pump. After that was changed the car started right up. I only ran it for a minute or so as the car had been sitting for a while and all of the maintenance items needed to be done. What has been done since:

-Pulled engine and changed rod and main bearings
-All seals, all new sensors, new Lindsey Rings, new headgasket, rebuilt the head and milled it flat, new water pump, new oil pump
-Lindsey Rogue M-Tune
-New T04e Turbo
-Lindsey full engine controls harness (was having the same exact problem before the harness was changed, I thought frayed wiring was the problem)
-Rebuilt Throttle Body
-All vacuum lines, venturi delete, fuel vapor lines, charcoal canister delete, cycling valve delete, manual boost controller, tial 38mm wastegate
-Almost new 930 clutch and 951 pressure plate

Here is a link with a video showing the behavior the car is exhibiting (hopefully it works):
https://photos.app.goo.gl/BrNCbUY5HVhj7JmK7

What has already been checked:
-Compression, 125 across the board
-Running without TPS, Running without O2 sensor, Ref and Speed Sensor distance, Swapped injectors to stock and change map setting

I am inclined to think it is something with the speed and reference sensor but the car starts right up.

Please let me know any suggestions you have, I am completely lost. Thank you in advance!

tempest411

In no particular order: check the AFM (including the temp sensor), and the DME (the ECU, not the relay). I'm assuming you already changed the coolant temp sensor. These are all prime suspects when symptoms like those you're having come up.

jwolfe

I know you mention all new sensors, was the throttle position sensor one of them? That was the cause for my rough idle and not being able to rev past 2k rpms in any gear. Had a build up of water/oil/liquid in it so it was reading all wrong.

CyCloNe!

In conjunction with the other suggestions check your throttle cable and make sure it isn't stuck/frayed/splitting and make sure the throttle plate is closed before start up as well.

peanut

you have changed so many components that its extremely difficult to know what might be wrong.
What you do know is that everything is functioning otherwise the engine would not start at all.

I would dismiss the speed and reference sensor for a start if they were faulty the engine simply wouldn't start and neither of those components would exhibit the fault that you have .

My first guess would be fuel delivery thats where I would start. but before you do just use a pair of insulated electrical pliers and pull off each of the distributor connectors in turn one by one noting any difference in rpm.
Any of the cylinders that are not operating correctly will show little if any change in revs indicating a fault . You should hear a distinct drop in revs with any of the cylinders that are operating correctly

Assuming that there is not an electrical or ignition issue for the moment

Try disconnecting the electrical connector to one of the injectors and see if there is any improvement or change in starting , idling or throttle pickup. There may be an under or over- fueling issue. If the running improves it would indicate an over-fueling issue but you should see other evidence of this like smoke, soot in the tail pipe and on the spark plugs so check these also.

I would order a cheap fuel pressure gauge which you can attach to the fuel rail and check your flow rate , fuel pressure and pressure leakdown time .
Don't forget to pull the vacuum hose off the FPR and check for any sign of fuel or smell of fuel which would indicate a leaky FPR diaphram causing a over-rich mixture

It has to be said that if the engine was running ok before you started your recent upgrade work then its likely you have disturbed something or altered some settings or parameters or there is a wiring fault so a thorough check of your work would be very useful in the process of elimination

thomasmryan

'non-running' implies old fuel to me. pop the engine side of the fuel filter loose and check the delivery rate and quality of the fuel. if it smells like varnish, pitch it.

peanut

fuel delivery rate should be measured at the fuel rail not the filter or you'll get a false flow rate figure.

thomasmryan

just trying to help. if the filters plugged that's is THE best place to check.

the crosspipe on the turbos can melt and choke down the flow also.

peanut

I wasn't being critical ...just thorough.
You cannot measure fuel delivery rate at the pump or filter because it is at the fuel rail that the fuel pressure is important...where it supplies the injectors.

If you measure the fuel pressure and flow rate at the fuel rail .......then it will be evident if there is an issue with a blockage or air leak or poor fuel pressure issue somewhere in the system.
The fuel pump and or filter are very commonly suspected to be an issue and changed only to find they were not the source of the problem at all its very rare indeed that a fuel filter is blocked enough to prevent an adequate fuel flow rate and system pressure