93 LT1 backfire when starting?
Thread Starter
Racer
Joined: Sep 2011
Posts: 462
Likes: 30
From: Riverside California
93 LT1 backfire when starting?
Hi guys..back to square one. When starting the engine I get a backfire. Crank it a second time and it fires, idle seems a bit ruff but settles in after giving it gas. In an earlier post Ithought it might be be the IAC but it checks out OK. However I have not pulled it out to see if it needs cleaning. Next on check list.
Within the last 500 miles I've changed plugs and checked wires, replaced injectors with Bosch III, Bosch O2sensors, MDS rotor and vented cap. Yesterday checked fuel pressure at the rail, checked great. No vacuum leaks?
Any advise would be a big help.
Within the last 500 miles I've changed plugs and checked wires, replaced injectors with Bosch III, Bosch O2sensors, MDS rotor and vented cap. Yesterday checked fuel pressure at the rail, checked great. No vacuum leaks?
Any advise would be a big help.
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Couple things that can cause backfires:
Intake:
- Lean condition (bad sensor, low fuel pressure, vacuum leak, etc.)
- Hanging valves or improper valve timing (over-tightened rocker arm, jumped timing chain, worn valve seats)
- Over advanced ignition timing (Distributor (optispark), sensor, crossed spark plug wires, bad ECM, etc.)
Exhaust:
- Rich condition (bad sensor, high fuel pressure, bad injector, etc.)
- Retarded ignition timing (Distributor (optispark), bad sensor, crossed spark plug wire, bad ECM, etc.)
- Slight misfire causing slow burn
- Hanging valves or improper valve timing (over-tightened rocker arm, jumped timing chain, worn valve seats)
- Exhaust leak
- Side effect of high flow exhaust systems
That's all I can think of off the top of my head.
Intake:
- Lean condition (bad sensor, low fuel pressure, vacuum leak, etc.)
- Hanging valves or improper valve timing (over-tightened rocker arm, jumped timing chain, worn valve seats)
- Over advanced ignition timing (Distributor (optispark), sensor, crossed spark plug wires, bad ECM, etc.)
Exhaust:
- Rich condition (bad sensor, high fuel pressure, bad injector, etc.)
- Retarded ignition timing (Distributor (optispark), bad sensor, crossed spark plug wire, bad ECM, etc.)
- Slight misfire causing slow burn
- Hanging valves or improper valve timing (over-tightened rocker arm, jumped timing chain, worn valve seats)
- Exhaust leak
- Side effect of high flow exhaust systems
That's all I can think of off the top of my head.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Check for codes. Check vacuum port of fuel pressure regulator for leaking fuel. Check digital coolant temp reading to be about same as outside temp first start of day. If its off 10 degrees you should look at engine coolant sensor or connector. If coolant is low; sensor may not read correctly since air doesn't transmit temperature like liquids. Good Luck
Thread Starter
Racer
Joined: Sep 2011
Posts: 462
Likes: 30
From: Riverside California
Check for codes. Check vacuum port of fuel pressure regulator for leaking fuel. Check digital coolant temp reading to be about same as outside temp first start of day. If its off 10 degrees you should look at engine coolant sensor or connector. If coolant is low; sensor may not read correctly since air doesn't transmit temperature like liquids. Good Luck
Thanks
Thread Starter
Racer
Joined: Sep 2011
Posts: 462
Likes: 30
From: Riverside California
Race Director
Joined: Mar 2015
Posts: 15,926
Likes: 579
Thread Starter
Racer
Joined: Sep 2011
Posts: 462
Likes: 30
From: Riverside California
How weird is this, went out and checked the plug wires in the right place. Then checked all the vacuum connectors,wiggled all the wires and cleared the old codes. Fired her up no problem, no backfire smooth idle. Took it for a ride got it hot, re started every time. No new codes. Only thing I can think of is the plug wires, I did move them around mostly at the distributor connections making sure they were plugged into the right port. i'll drive it a few
More times and re start it to see if the back firing has gone away. Will order up a new set of plug wires and hope for the best. Thanks for all the advice.
More times and re start it to see if the back firing has gone away. Will order up a new set of plug wires and hope for the best. Thanks for all the advice.
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Race Director
Joined: Mar 2015
Posts: 15,926
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How weird is this, went out and checked the plug wires in the right place. Then checked all the vacuum connectors,wiggled all the wires and cleared the old codes. Fired her up no problem, no backfire smooth idle. Took it for a ride got it hot, re started every time. No new codes. Only thing I can think of is the plug wires, I did move them around mostly at the distributor connections making sure they were plugged into the right port. i'll drive it a few
More times and re start it to see if the back firing has gone away. Will order up a new set of plug wires and hope for the best. Thanks for all the advice.
More times and re start it to see if the back firing has gone away. Will order up a new set of plug wires and hope for the best. Thanks for all the advice.
make sure the plug wires all click twice.