Engine quits after 7 minutes

[kieranod1]

Hi guys, when I cold start my 91 ZR1 she runs for approximately 7 minutes(warm up time) then shuts down. After that she starts right up for 6 seconds and shuts down. When she completely cools down I can start the whole process all over again, any thoughts?

[LGAFF]

good chance its O2 related its moving from open loop to closed loop, when its under 160 or so degrees it runs off a pre determined startup program, when it warms up it moves to running off the 02 sensors, and if they or the wiring is bad it will go rich or lean ... killing the car. I would bet if the car starts to stall and you gun the motor it comes right back because its going back to open loop

[kieranod1]

Thanks I'll try that.

[LGAFF]

Scan tool would help ID the problem

[kieranod1]

I'm not getting a check engine light and I'm not of a scan tool for OBD 1's. I do have a MaxiDAS DS808 reader with an OBD 1 adapter but still doesn't see anything.

[A26B]

Sounds to me like a primary fuel pump has failed


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[-=Jeff=-]

Sounds to me like a primary fuel pump has failed


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Was thinking the same thing..

[kieranod1]

I thought so also and replaced both fuel pumps and filter but still the same result.

[-=Jeff=-]

Did you check the fuel pump relays as well?

[kieranod1]

I'll get her up on the lift and check it out when I get back home. Thanks guys!

[WARP TEN]

Sounds to me like a primary fuel pump has failed


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I'm with Jerry--that would be my thought. --Bob

[A26B]

I thought so also and replaced both fuel pumps and filter but still the same result.



Have you tested rail pressure for each, individual pump at rail, since replacement?
Also verify primary pump fuse.


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[kieranod1]

Hi guys, back in town, checked the fuel pressure she is steady at 40 to 42 psi even after she shuts down. I put her up on the lift and the O2 sensors and wiring look good and intact. i also seem to have a vacuum leak because my secondary injector vacuum pump won't stop running.

[SAM/CH ZR-1]

I thought so also and replaced both fuel pumps and filter but still the same result.

Keep us informed where the problem is. Did you ever remove the plenum?

[tpepmeie]

I?m with Jerry. If you replaced the pumps and no change, check the FP1 fuse.


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[LGAFF]

Did you verify the O2 sensors are working properly and not just a visual?

[max76]

Some years ago my car has got about the same problem...check the yellow connector on the frame of the fuel pump assembly...my wires wasn't in good conditions...like if they were burn

[mhobtr]

I had this same problem and it turned out to be the primary fuel pump. The pumps had been replaced before and I didn't like the looks of their work so I bought an entire new OEM assembly. Installed it and...SAME PROBLEM!

Making a long story short, it turned out that the check valve on the new secondary pump wasn't working so when the secondary pump cut off, the primary pump back flowed into the tank.

Actually turned out that neither check valve in the new pumps worked so I replaced both and haven't had a problem since.

You might try installing a harness adapter to swap the pumps from primary to secondary to see if it corrects the problem. But, if both check valves are bad, as in my case, the problem will persist.

[kieranod1]

Thanks guys, the fuel pump fuse was fine, I will check the connector on the frame of the fuel pump assembly.I will also look into the check valve issue after I dive into the service manual. Thanks

[Paul Workman]

Normally, BOTH pumps run when the engine is first started, but if the FULL POWER mode is not activated, the secondary pump cuts off after 5 or so minutes. A fuel pressure ~ 45 psi and then dropping to zero at the moment the engine fails suggests the primary fuel pump has failed. Check the fuse(s) first (if you haven't already).

Kinda late to the party, but an easy way to "wring out" the fuel pumps is measure the current @ the fuel pump diagnostic connector.

Each pump normally draws 4-5 amperes for a total of 8-10 Amps with the ignition switch in the OFF position.

Place a fuel pressure pump on the fuel rail (to verify pressure later)
Place your VOM (red) jumper in the Amps position (see pic) and IMPORTANT! turn the switch to "A" (Amps) BEFORE making further steps/measurements. (Otherwise, you may damage the meter at worst, or blow the internal fuse at the least!)
Connect the (properly configured) meter between the fuel pump diagnostic test point (the little wire with a connector attached, jutting out of the wire loom (about an inch) by the windshield wiper motor, and the POSITIVE terminal of the battery.
If the reading is 8-10 Amps, and you can hear the pumps running, you will know that both pumps are running, verified by the pressure gauge attached to the fuel rail. But, if the reading is 4 or 5 amps, then one of the pumps is not running. (At that point, since the engine ran for several (7?) minutes before quitting, we can assume the secondary pump is running normally and the primary pump has failed.)

IMPORTANT! Soon as you're finished measuring current, remove the meter from the circuit and reconfigure the jumpers to reading VOLTS and switch the meter OFF or to another test scale. FAILURE to do so is the primary reason for a blown fuse inside the meter!

The first pic shows moving the (red) lead to the "A" (ampere) position, and the meter dial selection on the 10 Amps position.

The second pic shows a normal reading of 8.74 amperes for BOTH pumps (8-10 amps is normal, varying depending on which pumps are installed).

The 3rd pic show the little red wire sticking out of the wire loom close to the wiper motor. (pardon the yellow jumper wire connecting the black lead of the meter to the test connector at the wire loom).

[kieranod1]

Thank you Paul, I will try this out this evening and let you know. Again thanks for the help!

[kieranod1]

Hi Paul, just returned from the shop. I followed your procedure and I'm showing 7.1 on the meter and 60psi on the fuel pressure. Could there be something else going on?

[Paul Workman]

Hi Paul, just returned from the shop. I followed your procedure and I'm showing 7.1 on the meter and 60psi on the fuel pressure. Could there be something else going on?

The current reading, tho close to the low parameter, is a bit lower than I'd like. I'd want to investigate the pumps individually - just for grins...

So, to check the pumps individually, pull the fuse for one of the pumps (either one) and measure the individual current draw (the current draw is additive so subtracting the draw of one from the total will give you the draw for the other).

FUEL-AIR-SPARK! Something is missing...

So, if the fuel pressure remains at 45 ? when the engine quits, then my suggestion is to conduct your own dynamic scan (to record "before & after" data), or employ a shop with the scanning ability - as the logical way to "cut to the chase".

(My scanner (AutoXray) does have the capability described, but is no longer available. However, there are some shops with OBD-I scanning ability, AND Dominic or Marc or Pete and others can suggest software and a tablet, etc. to set you up to scan you Z. (Money spent fort the capability to perform static and dynamic monitoring is well worth every penny!).

[kieranod1]

Hi Paul, just came from the workshop, I started the Z and pulled the FP1 fuse and she kept running. Both pumps are new so I'm wondering if the relay may be faulty but I can't find the location in the shop manual, can you help or am I on the wrong track?

[max76]

Hi Paul, just came from the workshop, I started the Z and pulled the FP1 fuse and she kept running. Both pumps are new so I'm wondering if the relay may be faulty but I can't find the location in the shop manual, can you help or am I on the wrong track?

Do you check mthe yellow connector above fuel pump assembly?

[A26B]

Hi Paul, just came from the workshop, I started the Z and pulled the FP1 fuse and she kept running. Both pumps are new so I'm wondering if the relay may be faulty but I can't find the location in the shop manual, can you help or am I on the wrong track?

If the engine is cold, the engine will continue to run on the Secondary Pump, until the engine warms up to 160~170F ( I have forgotten the exact temp). Then, the secondary pump will shut down. What you did, only proves the Secondary Pump is working. It does nothing to verify the Primary Pump.

So, at cold start, if you either (1) let it continue to run with the FP1 fuse removed, until the Secondary Pump shuts down automatically, or (2) pull only the FP2 fuse, you can determine whether the Primary Fuel Pump is functioning properly. Engine dies, Primary Pump is not functioning properly.

You have been advised previously to test each individual pump separately with a fuel pressure gauge at the rail, key on, engine off & monitor leakdown for a couple of minutes.. Testing fuel pressure with both pumps operating together when the engine is cold will only tell you that at least one pump is functioning.

[LGAFF]

I think at this point i would be pulling and replacing 2 pumps ?for the 125 bucks and 25 minutes it would be worth it

[kieranod1]

To all you guys out there, I'm sorry for doubting you! You were right, my new #1
fuel pump had failed. I have it on the bench now and just need to source a new one, any recommendations? Thanks for all your help this, is a cool website and you guys are the pro's.

[tpepmeie]

If the engine is cold, the engine will continue to run on the Secondary Pump, until the engine warms up to 160~170F ( I have forgotten the exact temp). Then, the secondary pump will shut down. What you did, only proves the Secondary Pump is working. It does nothing to verify the Primary Pump.

The primary pump will shut off at 80C, or about 177F coolant temp. (It's not time limited, per se, but the OP said about 7 mins, which could coincide with the engine warm up time to 80C).

Also, merely having the Full Power key on does not signal the 2nd pump to turn on. After the warmup period, the 2nd pump is commanded on at a certain "relative fuel demand", ie high engine load.

I am convinced there is a failure of the primary pump, or that circuit.

updated: Looks like our posts crossed, I see you have diagnosed the problem.

[dredgeguy]

To all you guys out there, I'm sorry for doubting you! You were right, my new #1
fuel pump had failed. I have it on the bench now and just need to source a new one, any recommendations? Thanks for all your help this, is a cool website and you guys are the pro's.
RockAutoP-240KC
https://www.rockauto.com/en/parts/performance+electric,P240KC,fuel+pump,6256

[Paul Workman]

To all you guys out there, I'm sorry for doubting you! You were right, my new #1
fuel pump had failed. I have it on the bench now and just need to source a new one, any recommendations? Thanks for all your help this, is a cool website and you guys are the pro's.

No problem. It is easy to assume a new part is working (has to be, right!?). But, truth is "infant mortality" is the #1 failure mode, even before MTBF (Mean Time Before Failure - a term statisticians use to define FAILURE RATE.)

Anyway, you're not alone. I replaced my pumps and one of them was "kaput" out of the box. The pumps drew enough current, but the check valve on one was completely "shlect"; threw me for a loop at first until I put the pressure gauge on the fuel rail: then it was obvious something was very wrong (still!) with the pumps. (I pulled the pumps, and with a piece of rubber tubing, I blew pressure with my mouth against the check valve. Sure enough, one of the check valves passed air backward easy as you please.) Never assume!!!

[mhobtr]

I wonder if there's any way to get the check valves unstuck.

I got two brand new OEM with bad valves that I couldn't return. Haven't had the heart to throw them away because I keep thinking that someday someone will post "That's not a problem, you just................!"

[kieranod1]

Hi guys, thanks for your help, the Z is up and running again!

[max76]

Hi guys, thanks for your help, the Z is up and running again!

What was the problem?

[kieranod1]

Fairly new primary pump failed

[Paul Workman]

Yep! Several sources on failure rate Mean Time Before Failure (MTBF) refer to that phenomenon as "Infant Mortality". Just about everybody that endeavors to DIY repairs (me included) has fallen victim to installing a part, and just because it was a new part, assume it can't be the fault of the new part:

"It can't be the (whatever), cuz I just replaced it!" [-X Always verify operation, especially if the problem remains, OR (worse) if the symptoms return shortly thereafter!!