85 cad 4.1 backfiring through throttle body. replaced wires,plugs,cap,rotor,same problem has strong blue spark on #2 and #8 plugs #4 and #6 spark, yellow and very very weak can hardly see it where the other plugs you can hear it and watch it jump 3 inches . could the coil or the ECM be breaking down and causing this? this one has me puzzled. I have had this before on different cars and one the cam lobe was wiped off and one of the others the rocker arm had come off the push rod and and have seen bent push rods cause this problem,but no fire or hardley any fire on 2 cylinders seems funny. any ideas? thanks in advance
An expert who has achieved level 3 by getting 1000 points
An expert that got 10 achievements.
An expert that got 5 achievements.
An expert whose answer got voted for 500 times.
Re: backfiring through throttle body
It could also be that either the timing chain jumped because of worn teeth or the gear on the distributer might be worn as well . i would check this first. you can always pull the valve covers to check the rockers to make sure they are not real loose, but chances are you would have noticed that right away. if it were the coil you would not have a strong spark on any of the cylinders and it would probably real hard to start. due to the age of the vehicle it's possible the ecm is on it's last leg, but before i would look at that i would check all the other things first. if it is the ecm you can get a used one at a salvage yard for around 200 bucks . it will cost you a mint at the dealership. hope this helps. please rate this thanks.
a 6ya Mechanic can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repair professionals here in the US. click here to Talk to a Mechanic (only for users in the US for now) and get all the help you need. Goodluck!
- If you need clarification, ask it in the comment box above.
- Better answers use proper spelling and grammar.
- Provide details, support with references or personal experience.
Tell us some more! Your answer needs to include more details to help people.You can't post answers that contain an email address.Please enter a valid email address.The email address entered is already associated to an account.Login to postPlease use English characters only.
Tip: The max point reward for answering a question is 15.
You seem to be describing a flat spot - a hesitation during initial acceleration that is commonly caused by either insufficient spark power or the fuel system being slow to adjust to the new requirements.
A backfire is an explosion in the exhaust system and I wonder if you really meant a spit-back (through the intake), which is common with a fuelling caused flat spot?
Replacing the spark plugs is merely half the job and testing the spark power is the other half...
I suggest you check the fuel pressures and pressure regulator function and the injector spray patterns. Only if all tests good it could be worth testing the oxygen sensor...
100 psi per cylinder is way too low--should be in the vicinity of 150-165 per cylinder
back firing indicates wrong firing order and as you have replaced the plugs etc check that you have the leads on the correct plugs in the correct order
the timing for the engine should be around the 10 degree btdc and not tdc
When you state you have a "Cap & Rotor", indicating an engine, which may possibly be OLDER than the 1994 S-10 it is in. A Crank positioning sensor, on a full throttle body, (or do you mean carburetor/combo/injector system) Not the true name, but, in appearance, looks like a carb. It has a "pulsating" injector within the opening of the butterfly/mouth of the throttling body. When you have an ECM, or Computer Command timing, with a crank sensor, you will have 2 coil packs for 4 cylinder, a 3 coil pack for a V-6. They will be just under the electric cooling fan for the radiator. If you are driving a "bought used" vehicle, and the Cap, Rotor, & wires are only accessed thru the RH wheel well, it is a "Distributor System" & an OLDER engine. The Back fire is being caused by a "jumped" timing belt, or HOPEFULLY, a crossed spark plug wire.
Hello! Even though you have replaced coil, cap, rotor, plugs and wires; I need to know that you have a strong blue spark at a plug...Have you checked a plug for spark? I don't want you to misunderstand why I'm asking you that question; Certainly not to insult your knowledge but I need to know for sure that there is a strong spark...Guru..............Saailer
You may have got the spark plug wires out of sequence.
Reseat the coil wire going to the center of the distributor cap
Check the spark plug wires at the distributor against the firing order as follows:
The spark plug firing order is 1 - 4 - 2 - 5 - 3 - 6
The distributor rotor turns CLOCKWISE The engine cylinders / spark plugs are numbered :
firewall 3 - 6 2 - 5 1 - 4 front
300 CODES ARE IGNITION CODES THE 4 IS THE CYLINDER THAT HAS THE PROBLEM, CHECK THE SPARK PLUG FIRST TO SEE IF IT IS BLACKENED IF IT IS OK CHECK THE WIRE, GO TO AN AUTO PARTS STORE AND BUY A SPARK TESTER INSERT ONE END INTO THE SPARK PLUG WIRE UNTIL IT STOPS. ON THE OTHER END WILL BE A DIAL, DIAL IN THE GAP FOR THE PLUG. ALSO THERE IS A WIRE WITH A CLIP THIS IS GROUND. CLIP IT TO A METAL PART. HAVE SOMEONE START THE ENGINE AND IF THE SPARK IS STRONG AND BLUE IN COLOR YOU HAVE A GOOD WIRE. IF IT IS NOT STRONG AND WHITISH IN COLOR YOU NEED TO REPLACE THAT WIRE.
Check for the following: 1-Emissions system not fuctioning properly,2-Fault in the fuel or electrical system,3-faulty ignition system(craked spark plugs insulation or faulty plug wires)4-vacum leak at the trotlle body,intake manifold or vacum hoses,5- valve sticking,6-crossed plugs wires,7-valve timing incorrect. Hope this info helps. sammyc47.