'86 944 Turbo
Vitesse MAF
Siemens 80 lb injectors
how many lbs of pressure should be at my fuel rail when jumpering 30 and 87b on the dme relay socket?
The reason I ask is I am running rough under load - but it seems like it only happens intermittently. At first I thought it was my torque tube bearings, but I'm leaning more towards maybe an injector problem or possibly not enough fuel delivery.
Fuel pressure for 80 lb siemens fuel injectors
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Tom
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When these cars stumble and run rough under load, it's often/usually a weak ignition. How old is you cap, rotor, plugs, and wires. Wires are the easiest to over look, and have caused stumbled on my car more than once. I change them every two years (around smog time) to avoid that issue.
The Vitesse stuff is set up for a 3 bar FPR, so look for 43.5psi above the reference pressure/vacuum on the vacuum port.
The Vitesse stuff is set up for a 3 bar FPR, so look for 43.5psi above the reference pressure/vacuum on the vacuum port.
I have right around 43 psi on the fuel rail - how do I measure how much that is above the reference pressure/vacuum on the vacuum port?
My leakdown test after 20 minutes had pressure holding at about 28 lbs
If I adjusted the fuel pressure regulator to give 45 or even a little higher at the rail, would that be detrimental?
I will do some ignition component tests on it too.
My leakdown test after 20 minutes had pressure holding at about 28 lbs
If I adjusted the fuel pressure regulator to give 45 or even a little higher at the rail, would that be detrimental?
I will do some ignition component tests on it too.
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Tom
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If the engine is not running, that's about right. Raising the fuel pressure will just make it a little richer across the board, but the O2 sensor will likely negate that until you hit the WOT maps. How's your ignition?notny41 wrote: Fri Nov 10, 2023 7:50 am I have right around 43 psi on the fuel rail - how do I measure how much that is above the reference pressure/vacuum on the vacuum port?
My leakdown test after 20 minutes had pressure holding at about 28 lbs
If I adjusted the fuel pressure regulator to give 45 or even a little higher at the rail, would that be detrimental?
well, here is the beauty of having two cars. I can swap some parts back and forth. I'll try wires, cap and rotor. I also have a spare coil sitting around that tests good on the multimeter that I'll probably swap in there too. Will be back with results.
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Tom
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When my car starts to stumble on boost, a new set of NGK plugs gapped to .28 usually fixes it, but more than once I've had seemingly good wires cause the issue. I learned this on my old RX7TT. I hunted endlessly for the stumble and eventually took it to the dealer. Their head tech drove it, tested nothing, and immediately changed the wires to fix the issue. I overlooked them because they 'looked' new. It was a known thing on those car due to under hood temps, but has happened more than once to me on the 951.
I was hoping not to have to bump up the fuel pressure because it is already kind of stinky when I pull into the garage and shut the engine off - my assumption is that pungent smell is due to a rich condition. Not sure if that is a solid assumption or not but I'll try hunting ignition first before adding any fuel pressure.
well, I swapped out the coil as that was the easiest thing to do since I didn't need to pull any parts off the other car to do it. I haven't taken it out for a spin yet since doing that, but I did test the one that I pulled out. The secondary tested fine 5.43 k ohms - but it was just barely out of spec on the primary side at .7 ohms, where the range is supposed to be .4 - .6 ohms. So I'm crossing my fingers - but not exactly holding my breath. 
The coil I replaced it with tested at 5.54 k ohms on secondary and .6 ohms on primary.
The coil I replaced it with tested at 5.54 k ohms on secondary and .6 ohms on primary.
took it out today. it does seem quite a bit better - still not perfectly smooth. ordered some new plugs and wires too. will report back after those are put in. i feel like this thread is now maybe titled incorrectly. lol