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Hot start issue - '88 305 TBI L03

Old 05-17-2019, 05:13 PM
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Hot start issue - '88 305 TBI L03

I've been having a hot start issue with my 1988 Chevrolet Camaro 5.0l 305 TBI (L03) for a few years now, but things have been getting pretty bad with it this year and it's gotten to the point where I need to start finding a fix for the cause(s).

When cold starting the car, it starts right away every time, runs great for as long as you want to run it, until you shut the car off and leave it sit for 30-90 minutes. Then, when you go to start it, it will start right up, RPMs will go up to 1500, and then rapidly go down to 0 and the engine will quit. Subsequent starts (10-15 additional starts) will also start the engine right away, with the engine killing within a couple of seconds. If you hold the gas down to half throttle or if you "pump" the gas, it seems like the entire ignition system is cutting out as the engine struggles to stay running before killing again. After a while, it seems to "kick out" of that mode, and then the engine runs perfectly fine again. Usually, no SES light is set, but last night (May 16th), the SES light did finally illuminate, and here's what I got for codes:

14 Shorted Coolant Sensor - The ECM supplies 5 volts to sensor and measures voltage drop. Voltage reads high when cold (high resistance) and low when hot (low resistance). ECM uses reading to calculate temperature.

15 Coolant Sensor - The ECM supplies 5 volts to sensor and measures voltage drop. Voltage reads high when cold (high resistance) and low when hot (low resistance). ECM uses reading to calculate temperature.

23 Air Temp Sensor Open - The ECM supplies 5 volts to sensor and measures voltage drop. Voltage reads high when cold (high resistance) and low when hot (low resistance). ECM uses reading to calculate temperature.

43 ESC Failure - The Knock Sensor, located in engine block, detects vibrations in engine. ECM receives signal from knock sensor via the ESC module (in engine compartment) or MEMCAL (in ECM). ECM then retards ignition timing to control spark knock.

When engine is idling at 900 RPM after the engine starts running again correctly after warm start (during closed loop), coolant temp reads out at 192, O2 sensor swings between 0.15 and 0.99 at idle, TPS at 0.62 (at closed throttle), BLM 135, and MAP 07.

Bringing RPMs up to 2075 RPMs, the O2 sensor swings between 0.35 and 0.88, TPS at 0.97, BLM 130, and MAP 09.

The distributor cap and rotor are new as of last year. Plugs and plug wires look good. The passenger side fuel injector seems a bit leaky but still sprays fuel. I've read that some people correct hot start issues by replacing the ECT (Engine Coolant Temperature) sensor in these cars. Is that a reasonable first step in troubleshooting this issue? Is there any other reason why the ignition would seem like it's cutting out after a hot start, and then all of a sudden the car "snaps out of it" after 15 start attempts?

Thanks for any help you can offer!

Brian
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Old 05-17-2019, 07:34 PM
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Re: Hot start issue - '88 305 TBI L03

I'll be interested to read what some of more accomplished diagnosticians think.

My "guess" based on what you have presented is that no, a coolant temp sensor (CTS) would not help on a hot start, as your data shows a proper reading when hot. Still, there's a code for it. What is the CTS value when cold? Have you checked these values when the engine is acting up?

Could be an intermittent fault in the CTS, or in it's wiring. Both a cheap repair, so hopefully your issue is there.
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Old 05-18-2019, 07:10 AM
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Re: Hot start issue - '88 305 TBI L03

Have your Ignition Control Module checked or do a search on the forum for it.
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Old 05-19-2019, 03:15 PM
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Re: Hot start issue - '88 305 TBI L03

Originally Posted by antares57 View Post
Have your Ignition Control Module checked or do a search on the forum for it.
There is no "check" that can tell you the module is good. There are tests that can tell you the module is defective. This is better than nothing, but not really adequate.




1. What scan tool are you using?

2. What is the fuel pressure during the two-second "prime"? What is the fuel pressure at cold idle? What is the fuel pressure at hot idle? What is the fuel pressure at full-throttle, high speed?

3 Two codes for coolant temp? I'd inspect the sensor AND the wire harness.

4. A code for intake air temp? Is there even a sensor for that? I'm fairly sure my '88 K1500 LO5 does not have an intake air temp sensor.

5. Have you verified the Idle Air Control system? Cleaned the passage in the throttle body with aerosol carb spray? Seen the pintle move on the IAC? What is the commanded idle speed vs. the actual idle speed when cold? When warm?

6. Have you checked for the common TBI base-gasket failure? (I'd expect constant problems if the gasket failed--but checking this is simple and easy, especially if you sneak the TBI unit off the manifold without disconnecting the fuel plumbing--or while doing fuel pressure testing where you have the pressure hose removed anyway.)

7. Does the timing retard if you tap the intake manifold with a sturdy brass hammer? In other words, does the knock sensor system work?

8. If you disconnect the one-wire "ignition timing" connector, do you still have problems with stalling? The engine won't run "right", but does it still stall when warming-up?

9. I'd buy a tankful of TOP-TIER fuel (high detergent) and add a 20-oz bottle of Techron. Drive the vehicle until the tank is near empty, then repeat. Buy Top-Tier fuel regularly from then on. This MIGHT clean your "leaking injector".

10. If all else fails, consider a replacement ignition module--Delco or QUALITY aftermarket, not cheap crap. They can make sparks but not be working properly.
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Old 05-20-2019, 09:28 AM
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Re: Hot start issue - '88 305 TBI L03

Originally Posted by Schurkey View Post
4. A code for intake air temp? Is there even a sensor for that? I'm fairly sure my '88 K1500 LO5 does not have an intake air temp sensor.
Trucks/vans never got them, F & B body cars did. This connector is usually broken and easily unplugs when the air cleaner is removed. Then forgetten to be plugged back in upon air cleaner installation.
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Old 05-23-2019, 01:06 PM
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Re: Hot start issue - '88 305 TBI L03

I had the SAME EXACT problem many years ago: Root cause was a ruptured intake hose that sucked gas from inside the tank into the fuel pump.

Had the car diagnosed with computer scanners seven ways until sunday and techs couldn't figure it out. Took the car to an old school mechanic and he figured it out in a couple of hours. The hose rupture was small but would expand over from friction (gas running through it) which explained why it cold starts were fine but warm starts were not.

Replaced the hose (and the fuel pump) and haven't had any problems since - make sure when you replace the pump you align the level sender (mine's an 8th of a tank off so its actually empty when the gauge shows a bit of gas). The diagnosis would have been real easy if GM installed a schrader port on the fuel rail so you can plug in a gauge to check pressure but there was none. Since then I replaced the stock fuel rails with braided hoses and added a gauge so I can read the pressure.

Hope this helps.
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