Carpokes

Tom wrote: Wed Feb 25, 2026 7:58 am Does the boost gauge go to 1 when you turn on the key? This is a good proxy for whether the DME is getting power.

Does the tach bounce or twitch when you crank the motor? This is a good proxy for speed and ref sensor (harness) health.

Why do you say the speed and ref sensors are good and that it has fuel?

zooklm1 wrote: Wed Feb 25, 2026 9:26 am

Tom wrote: Wed Feb 25, 2026 7:58 am Does the boost gauge go to 1 when you turn on the key? This is a good proxy for whether the DME is getting power.

Does the tach bounce or twitch when you crank the motor? This is a good proxy for speed and ref sensor (harness) health.

Why do you say the speed and ref sensors are good and that it has fuel?

Boost gauge goes to 1 with turning the key to on. Tach twitches when cranking and I check the resistance for both speed and ref sensors (900 ohms each - were replaced 3 years/8k miles ago). Has fuel because I had a minor leak from when I reinstalled the fuel rail (due to having a minor leak prior to taking the intake manifold off to replace the battery cables and alternator to starter cable). The initial fuel leak was interesting because I originally thought injector 3 was leaking. Turned out that the threads in the rail mounting hole on the intake by cylinder 3 were failing and the bolt was not tight. I put in a helicoil and it is good.

Tom wrote: Wed Feb 25, 2026 9:40 am

zooklm1 wrote: Wed Feb 25, 2026 9:26 am

Tom wrote: Wed Feb 25, 2026 7:58 am Does the boost gauge go to 1 when you turn on the key? This is a good proxy for whether the DME is getting power.

Does the tach bounce or twitch when you crank the motor? This is a good proxy for speed and ref sensor (harness) health.

Why do you say the speed and ref sensors are good and that it has fuel?

Boost gauge goes to 1 with turning the key to on. Tach twitches when cranking and I check the resistance for both speed and ref sensors (900 ohms each - were replaced 3 years/8k miles ago). Has fuel because I had a minor leak from when I reinstalled the fuel rail (due to having a minor leak prior to taking the intake manifold off to replace the battery cables and alternator to starter cable). The initial fuel leak was interesting because I originally thought injector 3 was leaking. Turned out that the threads in the rail mounting hole on the intake by cylinder 3 were failing and the bolt was not tight. I put in a helicoil and it is good.

If it is still leaking fuel, fix that first. Either way, a leak at the rail would suggest there is fuel pressure in the rail, but would not necessarily tell you if the injectors are firing. The injector harness wires suffer the same frayed wires under the rubber boots as the speed and ref sensors and, if any one of them shorts out, none of the injectors will fire. See here for more on that. You might try rattling the injector wires while cranking. Or seeing if you can get starter fluid to sputter/run a bit (which would suggest sparks ok and fuel delivery isn't, or possibly super big vacuum leaks causing the AFR to be way off). Or checking the resistance between the two pins on each connector, looking for a direct short.

zooklm1 wrote: Wed Feb 25, 2026 10:13 am

Tom wrote: Wed Feb 25, 2026 9:40 am

zooklm1 wrote: Wed Feb 25, 2026 9:26 am
Boost gauge goes to 1 with turning the key to on. Tach twitches when cranking and I check the resistance for both speed and ref sensors (900 ohms each - were replaced 3 years/8k miles ago). Has fuel because I had a minor leak from when I reinstalled the fuel rail (due to having a minor leak prior to taking the intake manifold off to replace the battery cables and alternator to starter cable). The initial fuel leak was interesting because I originally thought injector 3 was leaking. Turned out that the threads in the rail mounting hole on the intake by cylinder 3 were failing and the bolt was not tight. I put in a helicoil and it is good.

If it is still leaking fuel, fix that first. Either way, a leak at the rail would suggest there is fuel pressure in the rail, but would not necessarily tell you if the injectors are firing. The injector harness wires suffer the same frayed wires under the rubber boots as the speed and ref sensors and, if any one of them shorts out, none of the injectors will fire. See here for more on that. You might try rattling the injector wires while cranking. Or seeing if you can get starter fluid to sputter/run a bit (which would suggest sparks ok and fuel delivery isn't, or possibly super big vacuum leaks causing the AFR to be way off). Or checking the resistance between the two pins on each connector, looking for a direct short.

Yep, fuel leak fix was the top priority. I was thinking about the injector wiring and will check the resistance between pins in the connector when I get home. Thank you for the pointers

zooklm1 wrote: Wed Feb 25, 2026 7:09 pm

zooklm1 wrote: Wed Feb 25, 2026 10:13 am

Tom wrote: Wed Feb 25, 2026 9:40 am

If it is still leaking fuel, fix that first. Either way, a leak at the rail would suggest there is fuel pressure in the rail, but would not necessarily tell you if the injectors are firing. The injector harness wires suffer the same frayed wires under the rubber boots as the speed and ref sensors and, if any one of them shorts out, none of the injectors will fire. See here for more on that. You might try rattling the injector wires while cranking. Or seeing if you can get starter fluid to sputter/run a bit (which would suggest sparks ok and fuel delivery isn't, or possibly super big vacuum leaks causing the AFR to be way off). Or checking the resistance between the two pins on each connector, looking for a direct short.

Yep, fuel leak fix was the top priority. I was thinking about the injector wiring and will check the resistance between pins in the connector when I get home. Thank you for the pointers

Any one have a good vacuum line diagram they can post? I ended up having a broken Y and that has me questioning my routing for both fuel and accessories connections.thanks

speedy951 wrote: Thu Feb 26, 2026 6:36 am I bought the following two items to make an adapter from M12 fitting on the end of the fuel rail to a schrader valve to check fuel pressure.

https://www.amazon.com/Universal-Alumin ... JFSW&gQT=1

https://switchsuspension.com/1-8-female ... le-plated/

danmartinic wrote: Thu Feb 26, 2026 7:50 am

speedy951 wrote: Thu Feb 26, 2026 6:36 am I bought the following two items to make an adapter from M12 fitting on the end of the fuel rail to a schrader valve to check fuel pressure.

https://www.amazon.com/Universal-Alumin ... JFSW&gQT=1

https://switchsuspension.com/1-8-female ... le-plated/

Yes that's it--M12 x 1.5 which is less common than 1.25 pitch

Thanks for reminding me.. need to get one of these adapters.. though not sure how you are using the schrader valve? Wouldn't M12 to 1/4 NPT be easier to adapt to regular pressure gauges?

Have to say that in 18 years and over 250k I've never needed to check fuel pressure...