So I replaced the valves and head gasket on my 92 miata and now it’ll crank but wont start. The fuel pump is only getting 7 volts and wont turn i on replaced the relay and checked all the grounds i took off. Just wondering what i should be looking for and how to fix it
Motor is timed right? You have checked compression? You are getting spark at plugs? You had head off. And are looking at fuel pressure first?
4 Likes
I would start by confirming a good ground path back to the battery. You can use your meter in voltage measuring mode and connect from the pump ground to the battery ground. If you read any voltage, there is a bad ground that needs attention. If not, then start marching the positive lead back from the pump to the battery, checking for where the voltage drop(s) are in the positive wire connections. This needs to be done with the pump operating and drawing current as often the voltage drop doesn’t happen unless there is a load on the bad connection…
3 Likes
+1 for grounds
Sounds like you need to slowly retrace all the wiring done, as well as any connectors you unplugged/plugged back in for bent pins …
You can use jumper cables to go from the neg battery terminal to a metal bracket on the engine and see if that helps, or from the neg battery terminal to the chassis (frame), or chassis (frame) to engine, if one of those help it then start looking very close at the grounds between the two that helped…
1 Like
Yup timings all good and so is spark checked all those first only problem (that i know of) is the fuel pump
Are you getting spark to the plugs? I didn’t see if you checked compression or not as mentioned by @Carvell. Compression is CRITICAL. Pull a plug and see if it’s wet or dry.
Yup compression is all good and the plugs are dry
Are you getting spark? Dry plugs tells me you may not be getting fuel.
1 Like
Ain’t got no gas.
1 Like
Suggst to focus on why you only measure 7 volts at the fuel pump. You should measure close to battery voltage, at least 11 volts when pump is running. Are you able to post a copy of the wiring diagram/schematic for the fuel pump circuit? If so, you’ll likely get better help here.
Ground problems after major engine work not that unusual, b/c easy to forget to reconnect all the grounds. Engine block needs to be robustly connected to chassis. Likewise cylinder head to chassis. And the battery ground cable to chassis. Check all three. Any signs of poor ground connections, clean & retighten , fix. Battery must be good & fully charged of course.
Relay problem unlikely if car started pretty good before all this work.
2 Likes
When my 1996 Miata died while driving and would not start, the mechanic told me that the fuel pump was not getting a ground, and that the ground was set through the ECU. I sent the ECU for repair and re-programming, and it solved the problem. I believe these ECUs are known for capacitors that deteriorate.
1 Like
If the compression is good, and there is spark at the plugs, and the plugs are dry, then you have a fuel problem. You could spray starting fluid into the air intake and see if it will catch and run for a few seconds. If it does you have even more confirmation. The fuel pump is in the tank, if I recall right, and the fuel filter is bolted to the frame near the right rear wheel.
Everyone’s ideas about using jumper cables as grounds are OK, but the battery is in the trunk so you need long cables.
I;m pretty sure you have a bad ground somewhere, but where?
You should join the forums at www.miata.net. There a people there who can help you.