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Discussion Starter · #1 ·
I am about to lose my mind. I acquired this 93 through an auction knowing it was sitting for about 12 years. The motor turned over. The fuel pump was shot so I replaced that. While i had my hands on it, I did the cap, rotor, plugs, wire, ICM, coil, fuel filter. Still no start. I would spray some starting fluid and it would choke but not run. I ordered a distributor since the original was rusty looking. I connected the two connections to the new distributor and grounded the bottom plate. I spun the shaft and still no pulse. I noticed the distributor was getting hot just sitting there while connected. I checked he voltage on the connections and the 2 wire connect read 12.4v and around 8.5v on the smaller wire. The 4 wire connection read 8.5v across all 4 wires. Any idea what it could be? I ordered a Throttle position sensor because I read that a faulty one can cause the computer to read a false WOT and cut the spark/fuel. I pulled the ECM from the passenger side kick panel and although i can see there was water/moisture contact (rusty spots) on the outside, the inside was clean and dry. The only issue I can consider a possibility with the ECM is I noticed the connection pins on the outside of the ECM seemed a little "coated" with that mildew looking stuff you'd find on some metals due to moisture. I cleaned the entire unit with contact cleaner, took a gentle wire brush and brushed the contacts inside and out. No luck.
 

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The bottom plate does not require grounding, although it should not make any difference. The module in the distributor may be faulty from new. Use white heat sink paste, not dielectric grease, on the replacement. Check the spark module on the side of the relay bracket at the right rear of the engine compartment. There is a Schrader port on the fuel line on top of the engine. I would check the fuel pressure to determine if you have a blocked fuel line, or bad pressure regulator in the TBI. The regulator membrane is easy to replace, and all you need to remove is the top cover of the TBI to access it. Make sure you have a set of new gaskets for the top, because they usually self destruct when you take the top off. You do not have to remove the injectors. When you spray starting fluid in the intake, you say it "chokes". Does that mean that it tries to start, but does not have enough fuel to actually run? If that is so, I would check the fuel pressure at the Schrader valve first. You need at least 9 psi to idle. The pressure usually hits about 12 psi to run under throttle. Less than that would indicate the pressure regulator as my first guess.
 

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Discussion Starter · #3 ·
The bottom plate does not require grounding, although it should not make any difference. The module in the distributor may be faulty from new. Use white heat sink paste, not dielectric grease, on the replacement. Check the spark module on the side of the relay bracket at the right rear of the engine compartment. There is a Schrader port on the fuel line on top of the engine. I would check the fuel pressure to determine if you have a blocked fuel line, or bad pressure regulator in the TBI. The regulator membrane is easy to replace, and all you need to remove is the top cover of the TBI to access it. Make sure you have a set of new gaskets for the top, because they usually self destruct when you take the top off. You do not have to remove the injectors. When you spray starting fluid in the intake, you say it "chokes". Does that mean that it tries to start, but does not have enough fuel to actually run? If that is so, I would check the fuel pressure at the Schrader valve first. You need at least 9 psi to idle. The pressure usually hits about 12 psi to run under throttle. Less than that would indicate the pressure regulator as my first guess.
Thanks for the quick response...

I ordered a new distributor from amazon and it came with the ICM. I also had replaced the original ICM with one and same issue. Do you have a picture of the "spark Module" I opened the Schrader Port and when attached a Pressure gauge. I was hitting about 11psi when it got primed. After about 3 seconds the pressure goes to 0. I rebuilt the regulator with new bladder and gaskets. Changed the injectors. When I was spraying it, it was choking but would just keep cranking but would never run regardless if I poured gas down the throttle.
 

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You can check spark with a timing light. Did you remove the connector on the right valve cover when setting the timing? It should be set on "0" on the harmonic balancer with the connector open.
 

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if the injectors arent firing while cranking, good chance the pickup coil is NFG. I would be weary of amazon distributors, a friend went through 2 of them recently before we just bought some quality parts and rebuilt his original.
 

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You can hear the injectors clicking, or use a noid light to check for electrical signal to the injectors. You should see a spray from the injectors when the engine is cranking (intake bread box off). Shine a flashlight on the spray to help see it. If the noid light is not lighting, the injectors are not getting a signal. Do good troubleshooting and do not just load the parts cannon, and blast away.
 

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Discussion Starter · #7 ·
if the injectors arent firing while cranking, good chance the pickup coil is NFG. I would be weary of amazon distributors, a friend went through 2 of them recently before we just bought some quality parts and rebuilt his original.
I just ordered a relacement distributor and a GM ICM to try and peice together a best possible option.
You can hear the injectors clicking, or use a noid light to check for electrical signal to the injectors. You should see a spray from the injectors when the engine is cranking (intake bread box off). Shine a flashlight on the spray to help see it. If the noid light is not lighting, the injectors are not getting a signal. Do good troubleshooting and do not just load the parts cannon, and blast away.
I tested the connections on the new injectors with a test light and found only one side was Hot while the other had neither hot or ground. I applied a quick tap with my power probe and the injectors do pulse. I also spun the new distributor with it just connected up and didn't have any pulse or spark.

So as of now, I'm waiting on an oil pressure switch, new distributor and ICM.
 

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The oil pressure switch only affects the fuel pump. The oil pressure switch is not closing, because there is no oil pressure, and disconnects the fuel pump. That is why the fuel pressure goes to 0 after a few seconds. Since you swapped the ICM in the current new distributor, you should just install the 2nd new distributor before swapping the ICM on it.
 
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pressure drops to 0 after shutdown because there is a bleed off orfice in the injector pod.

IE: this is normal operation for a TBI system

also, the oil pressure part of the fuel pump circuit is in parallel to the fuel pump relay. one or the other will allow power to the fuel pump. you can disconnect the oil pressure switch and as long as the relay is functioning the pump will still get power. i believe having the oil switch functional takes load off the relay and perhaps extends relay contact life but i have not read this in any GM literature. if the relay fails and the oil pressure switch is functional after enough cranking to get engine pressure over 3 psi, the switch will close and feed power to the pump. i believe this was in place so folks wouldn't get stranded if their fuel pump relay failed.
 

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The computer controls the fuel pump relay, and if the engine does not start, it will not further energize the relay. It bleeds down because the pump is not running.
 

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Factory Service Manual.

Page 6C-3; The electric fuel pump operation is controlled by the ECM through a fuel pump relay.

Page 6D4-4; Read across pickup coil leads. Should read 500-1500 ohms. Flex wires to determine intermittent opens. Read across pickup coil leads and base of distributor. Should read infinite.

Page 6E2-A-20; Circuit description: When the ignition switch is turned ON, the ECM will turn ON the in-tank fuel pump. It will remain ON as long as the engine is cranking, or running, and the ECM is receiving ignition reference pulses. If there are no reference pulses, the ECM will shut OFF the fuel pump within 2 seconds after key ON.
 

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that says nothing of why the pressure bleeds off. while you are partially correct correct that there is no pressure when the pump turns off. on a normal multiport system there is usually a check valve in the pump that keeps pressure in the system after shutdown, even if the pump is off. this is not the case with a TBI system. take a TBI injector pod apart and you will see what I'm talking about. i have personally brazed up this bleed off port and installed a TPI pump, and the system no longer bleeds down to 0 instantly. Infact it kept pressure for weeks.
 

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You may have modified yours, but the OP did not. They bleed down and that is what he needs to know. The TBI primes the system when the key is turned on.
 

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that picture is not modified, it is original. "The TBI primes the system when the key is turned on." this isn't what is being discussed here. OP stated the pressure drops to 0psi after shutdown. This is NORMAL operation. if you don't have the orfice in the throttle body as shown above the pressure would not bleed off instantly.
 

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You are right the pressure drops to 0 after the engine shuts off. It also drops to 0 if the ECU does not see an ignition pulse, and the ECU shuts off the pump.

I never said the picture was modified, you showed me a picture of an original one, but told me that you modified yours.
 

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Discussion Starter · #19 ·
Sorry for the long wait guys. I had put this 93 "Ratillac" and my 95 Impala SS project on the back burner for several weeks. Here and update on my 93 TBI Ratillac. I changed the Oil Pressure Switch located above the oil filter and gave it a shot but still didn't get an injector pulse. I had removed the distributor to see if it could be that. It was definably the original so I ordered a replacement from amazon. Of course it wasn't a proper fit so I ordered another one that was a REMAN. WHile waiting I pulled the ECM and noticed there was definitely water exposure since there were rust stains. I ordered a REMAN AC Delco ECM from Rockauto and swapped the factory E-PROM in. After getting everything installed and connect, I go to crank it and IT STARTS!!!!!! This baby purrs like a kitten and runs so smooth. Even the exhaust vapor was just clean steam and plenty of water droplets. No black or white smoke. I am so relieved. I definitley am more of the "parts cannon" type of guy when it comes to these older cars for one reason. If your going through the trouble of getting an older car up and running, why not just replace whats easily accessible while you're in there especially things that can eventually fail. I prefer having my old cars running like they're new. This is just my personal choice and preference to go about things. It may not be yours but to each their own. If you follow me on tik tok, you can see the video if you scan my QR code
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