91 z28 stalling under load
08-06-2018 | 12:13 AM
#1
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91 z28 stalling under load
I have a 91 z28 305 tpi, I’m about to give this sucker away. I’ve been having a issue with the car falling on its face after reaching operating temps under load, in reverse and also cruising at 30 letting off the throttle slowly. The car idles like a dream and when it hiccups under load the car snaps back and runs smooth from anywhere between 30-45 seconds then falls on its face again.
My buddy gave me a great price on it after her had a cam installed this issue persisted, uppon purchase I installed a new distributor, wires, fuel pump, fuel filter, injectors 19lbs, fpr, iac valve, vacuum lines, tps sensor manifold air temp sensor , i found both temp sensors disconnected and 3 grounds disconnected. Any ideas?
My buddy gave me a great price on it after her had a cam installed this issue persisted, uppon purchase I installed a new distributor, wires, fuel pump, fuel filter, injectors 19lbs, fpr, iac valve, vacuum lines, tps sensor manifold air temp sensor , i found both temp sensors disconnected and 3 grounds disconnected. Any ideas?
08-06-2018 | 09:08 AM
#3
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Re: 91 z28 stalling under load
TPS is reading .64 closed and 4.24 wot. I actually did put a ac Delco ECM. Sorry I forgot to mention that. Also the thing has no codes. Never one time has the light came on after start up
08-06-2018 | 11:20 AM
#5
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Joined: Nov 2004
Posts: 768
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From: Lansing, MI
Car: 1988 IROC-Z
Engine: 5.7 TPI
Transmission: 700R4
Axle/Gears: 3.45
Re: 91 z28 stalling under load
That is a high voltage for idle BTW. Should be around .54V but I don't see that being a huge issue.
I think the best thing you can do is get something to scan/log with and get 30 sec to a minute of data before and after the incident and capture the incident. This should allow you to see what is changing and give you a path to start diagnosis on.
I think the best thing you can do is get something to scan/log with and get 30 sec to a minute of data before and after the incident and capture the incident. This should allow you to see what is changing and give you a path to start diagnosis on.
08-06-2018 | 11:36 AM
#6
Joined: Dec 2004
Posts: 15,667
Likes: 725
From: Mile High Country !!!
Car: 1967 Camaro, 91 z28
Engine: Lb9
Transmission: M20
Axle/Gears: J65 pbr on stock posi 10bolt
Re: 91 z28 stalling under load
That is a high voltage for idle BTW. Should be around .54V but I don't see that being a huge issue.
I think the best thing you can do is get something to scan/log with and get 30 sec to a minute of data before and after the incident and capture the incident. This should allow you to see what is changing and give you a path to start diagnosis on.
I think the best thing you can do is get something to scan/log with and get 30 sec to a minute of data before and after the incident and capture the incident. This should allow you to see what is changing and give you a path to start diagnosis on.
have you checked your fuel pressure ?
https://www.thirdgen.org/forums/tran...ds-double.html
08-06-2018 | 11:57 AM
#7
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Joined: Nov 2004
Posts: 768
Likes: 32
From: Lansing, MI
Car: 1988 IROC-Z
Engine: 5.7 TPI
Transmission: 700R4
Axle/Gears: 3.45
Re: 91 z28 stalling under load
the spec for 90-92 tpi is .66-76vdc. The tach sounds like a separate issue.
have you checked your fuel pressure ?
https://www.thirdgen.org/forums/tran...ds-double.html
Last edited by KyleF; 08-06-2018 at 02:11 PM.
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08-06-2018 | 12:56 PM
#11
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Re: 91 z28 stalling under load
Btw I wasn’t just throwing parts at it. Everything had a reason, for instance the cap and rotar had corrosion, the icm was over heating and the heat sink was damaged, also why not throw a entire distributor with the new cam just my personal opinion. The car is 27 years old. Does not hurt to change the sensors entirely. The tps had dead spots while checking voltage with my fluke meter. The IAC valve was really rusty. The intake air temp sensor was really rusty after I wiped the sucker off. The fuel pump I did cause the sending unit was not working at all so why not throw 60 pump in the same time? Wires change them every 30k and Spark plugs aswell.
08-06-2018 | 11:10 PM
#14
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Re: 91 z28 stalling under load
Thank you for the tip on fixing the tach, resistor installed in like 20 mins. Tach reads steady 800 at idle. So I did notice the fans do not kick on and the car gets pretty hot. If I’m not mistaking that is the sensor passenger side between cylinder 6 and 8? The “fan switch” ? Could this be causing the issues while driving? Does the ecm use that info from the fan switch for air fuel mixtures?
08-07-2018 | 11:31 AM
#15
Joined: Dec 2004
Posts: 15,667
Likes: 725
From: Mile High Country !!!
Car: 1967 Camaro, 91 z28
Engine: Lb9
Transmission: M20
Axle/Gears: J65 pbr on stock posi 10bolt
Re: 91 z28 stalling under load
The sensor between 6 & 8 is the secondary fan switch. The cts in the front on the intake is used for cools start enrichment and correction once in closed loop.
08-07-2018 | 11:37 AM
#16
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Re: 91 z28 stalling under load
@tuned performance...
thank you for that info, I completely overlooked the thought of the primary CTS. The fans work when I jump the pins to read the codes but never when the car is warm. I’m getting a snap on computer from the snap on guy today so I can scope this sucker with the eagles eye
thank you for that info, I completely overlooked the thought of the primary CTS. The fans work when I jump the pins to read the codes but never when the car is warm. I’m getting a snap on computer from the snap on guy today so I can scope this sucker with the eagles eye
08-07-2018 | 12:04 PM
#18
Joined: Dec 2004
Posts: 15,667
Likes: 725
From: Mile High Country !!!
Car: 1967 Camaro, 91 z28
Engine: Lb9
Transmission: M20
Axle/Gears: J65 pbr on stock posi 10bolt
Re: 91 z28 stalling under load
Usually when the cts fails you get a code 15 . The fan switch is a thermal switch.
iirc the map kpa should be from 40-60 Kpa at idle. You have steady vacuum at idle with the cam swap ?
iirc the map kpa should be from 40-60 Kpa at idle. You have steady vacuum at idle with the cam swap ?
08-09-2018 | 02:10 PM
#20
Re: 91 z28 stalling under load
When I first got my car it would stall when it down shifted and hit over 3,000 rpms. Changing the oil yielded a "rotten egg" smell in the oil which indicates a bad catalytic converter. Deleting the cat solved both problems and allowed the exhaust to flow out at an optimal rate, so it stopped stalling at high rpms.
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