Crank but no start

[tiegsd]

Hello all,

Having a bit of a problem with the Z, she will crank all day, but won't kick over and run. Replaced the fuel pumps, have 51 psi on the fuel rail when pumps running. No codes, only code 12 when I jumper the ALDL pins.

I'm decent with electronics, but never been much of a car mechanic. Intend to just go through the FSM troubleshooting steps for the condition I have.

Background is that last year I was able to start and drive the car, but upon start it would run and the rpms would slowly drop and the engine would start to stumble and run rough after a few minutes. SES light would then come on, rpms would bump up for a second, then car would run smooth for a couple minutes. Then SES lig ht out, engine slowly drop, stumble and rough running until SES light on again, repeat process. Car did this even when warm and I was driving it.

Early this year, car wouldn't start anymore, but would crank. Thought maybe failing primary fuel pump, so pulled the assembly, checked winding resistances, primary pump was 115 ohms, secondary pump 5 ohms, so looked like failed primary pump, hence pumps replaced.

Additionally, battery would be flat after sitting for 2 weeks or so, ended up replacing battery, but still have crank but no start.

Wanted to see if anyone had seen these symptoms, or has a hunch on which way to go with troubleshooting?

Car is 1990, no mods other than Haibeck chip, VATS bypass.

Thanks in advance!

Sent from my SM-N920V using ZR-1 Net Registry mobile app

[Paul Workman]

FUEL- AIR- SPARK?

PRELIMINARY: (No reflection on your knowledge/skills. But, just some basic LT5 troubleshooting procedures that get to the point ASAP.)

The Factory Service Manual (FSM) and the troubleshooting charts can be very helpful: can be...is the operative phrase.

SCANNER: By FAR a static and dynamic scan is the way to getting down to "brass tacks" in a hurry! An OBD-I scanner is required, connected to the ALDL plug to scan for codes. The legacy codes can be cleared first by disconnecting the battery for 30 seconds or so, and then reconnecting the battery before reading the codes to see what pops back up. HONESTLY... Scanning is the quickest way to putting a finger directly on the symptoms. The shorting the ALDL pins can give you a static check, after the old codes are erased, but the scanner can log and show you 41 different checks in a couple seconds. So, if at all possible to access an OBD-1 scanner, I highly recommend it. (Mine stays in the glove box and rides w/me @ all times!)

FUEL:

Check the plugs first: Are we flooding?? If not wet w/ fuel, how do they look; are they dry and the color brownish?

Leak-down test: Ignition switch ON long enough to allow the pumps to charge the fuel rail. Then switch OFF. Pressure should be mid 40s psi (my 90 is ~45 psi) should hold that pressure to w/i one PSI for 20-30 minutes.
current draw verification
injector resistance verification
spark plug flooding inspection

AIR (not in question yet)

SPARK:

a "NOID" light will indicate whether you have spark or not. If not, you can pull a spark plug boot and insert a spare spark plug in it and tie-wrap (ground) the plug to the engine (ideally) and have someone spin the starter while you observe to see if you have spark. If not, refer to the FSM or troubleshooting procedure tree.

With ALL THAT SAID, your battery going dead in a couple days raises my eyebrow. If you have a VOM you'd want configure the leads to measure AMPERES. Once the battery is fully charged, you can disconnect a terminal (the negative is easiest to access) and measure the parasitic draw. Normally it will be around 25mA (.025A). Anything over 50mA is excessive and requires troubleshooting. (NOTE: Once the battery cable (either) is disconnected from the battery, the various capacitors in the radio and ECM will begin to discharge. So, when you initially connect the VOM to read current, you may likely get a surge that lasts for 1-3 seconds before settling back to ~25 mA. But, also be aware of the courtesy lights must be timed out.

Well... this is too long already. So, I'll pause here until you can do some preliminary checks first.

[tiegsd]

Originally Posted by Paul Workman

FUEL- AIR- SPARK?

PRELIMINARY: (No reflection on your knowledge/skills. But, just some basic LT5 troubleshooting procedures that get to the point ASAP.)

The Factory Service Manual (FSM) and the troubleshooting charts can be very helpful: can be...is the operative phrase.

SCANNER: By FAR a static and dynamic scan is the way to getting down to "brass tacks" in a hurry! An OBD-I scanner is required, connected to the ALDL plug to scan for codes. The legacy codes can be cleared first by disconnecting the battery for 30 seconds or so, and then reconnecting the battery before reading the codes to see what pops back up. HONESTLY... Scanning is the quickest way to putting a finger directly on the symptoms. The shorting the ALDL pins can give you a static check, after the old codes are erased, but the scanner can log and show you 41 different checks in a couple seconds. So, if at all possible to access an OBD-1 scanner, I highly recommend it. (Mine stays in the glove box and rides w/me @ all times!)

FUEL:

Check the plugs first: Are we flooding?? If not wet w/ fuel, how do they look; are they dry and the color brownish?

Leak-down test: Ignition switch ON long enough to allow the pumps to charge the fuel rail. Then switch OFF. Pressure should be mid 40s psi (my 90 is ~45 psi) should hold that pressure to w/i one PSI for 20-30 minutes.
current draw verification
injector resistance verification
spark plug flooding inspection

AIR (not in question yet)

SPARK:

a "NOID" light will indicate whether you have spark or not. If not, you can pull a spark plug boot and insert a spare spark plug in it and tie-wrap (ground) the plug to the engine (ideally) and have someone spin the starter while you observe to see if you have spark. If not, refer to the FSM or troubleshooting procedure tree.

With ALL THAT SAID, your battery going dead in a couple days raises my eyebrow. If you have a VOM you'd want configure the leads to measure AMPERES. Once the battery is fully charged, you can disconnect a terminal (the negative is easiest to access) and measure the parasitic draw. Normally it will be around 25mA (.025A). Anything over 50mA is excessive and requires troubleshooting. (NOTE: Once the battery cable (either) is disconnected from the battery, the various capacitors in the radio and ECM will begin to discharge. So, when you initially connect the VOM to read current, you may likely get a surge that lasts for 1-3 seconds before settling back to ~25 mA. But, also be aware of the courtesy lights must be timed out.

Well... this is too long already. So, I'll pause here until you can do some preliminary checks first.

Thanks for the comprehensive response, looks like I have a lot of work to do.

Will report back once I've made some progress on the list and hopefully ruled some things out.

Sent from my SM-N920V using ZR-1 Net Registry mobile app

[WARP TEN]

Pal's experienced response is great. But I would start with spark next since you have fuel. FMS is a big help as is a scanner.--Bob

[tiegsd]

Originally Posted by WARP TEN

Pal's experienced response is great. But I would start with spark next since you have fuel. FMS is a big help as is a scanner.--Bob

FSM seems to point you that way too (chart A-3, page 1 of 4). Def going to get a scanner and start learning how to use it, and make sure I'm not missing anything there.

Checked both fuel pumps this morning using test connector (since I hadn't done that yet; only checked Primary), and pulling fuses on at a time, both giving about 51 to 52 psi. Do have a leak though because pressure drops off back to zero with a minute or two when pumps shut off.

Appreciate the responses, will report in as I have more data.

[tiegsd]

Tested spark today, had spark, and car almost started down a cylinder, so for fun put plug back in and sure enough she started right up!

Took her out for a spin, ran perfectly. My dropping idle and stumble is gone, no misses, lots of power.

Still have fuel system leak to fix, and have ALDL reader coming for future.

Thanks all!

Sent from my SM-N920V using ZR-1 Net Registry mobile app

[Paul Workman]

Originally Posted by tiegsd

FSM seems to point you that way too (chart A-3, page 1 of 4). Def going to get a scanner and start learning how to use it, and make sure I'm not missing anything there.

Checked both fuel pumps this morning using test connector (since I hadn't done that yet; only checked Primary), and pulling fuses on at a time, both giving about 51 to 52 psi. Do have a leak though because pressure drops off back to zero with a minute or two when pumps shut off.

Appreciate the responses, will report in as I have more data.

Yes, you have a leak somewhere, but I doubt it is causing the main issue. Typically tho, barring a fuel line leak, it is either injector(s) or the check valves (one in each of the fuel pumps.

Project for another day: note worthy is all for now. The slow leak-down wouldn't cause the issue you've described so far.

Far as fuel lines go, the stock plastic clamps on the fuel pump assembly on mine was leaking, apparently. A stainless screw clamp end that issue. (Justa thought).

[Macroblock]

As the C4-ZR1's reach 30 years old, this is becoming a common issue. I prepared a few web pages that provide useful tips on how to diagnose a no-start issue.

http://zr1ecm.com/youfix.html