Backfiring Engine under load

[davebuc]

I just replaced the ignition sensor next to the coil. I then did a 4 plug wire spark gap test. No spark. I then did a spark gap test on the coil wire to top of dist cap. No spark there either. I then grounded the coil to the block with a screwdriver. Still no spark at the coil.

[davebuc]

It sounds like the timing gear set was not indexed correctly causing the valve timing to be way off. I would go back to the engine builder.

If the valve timing was off, wouldn't the cylinder compression numbers be less good than what they are?
1. 150 5. 145
2. 155 6. 145
3. 145 7. 145
4. 150 8. 145

[Paxdad]

If the valve timing was off, wouldn't the cylinder compression numbers be less good than what they are?
1. 150 5. 145
2. 155 6. 145
3. 145 7. 145
4. 150 8. 145

Yes. But the readings could also be better than what your are seeing especially if only off by several degrees in relation to the cam. Pull the distributor and check the drive gear as well. It has been some time since a built a motor so I don't want to come off as an expert nor lead you down a dead end path. But it seems like your issue is more mechanical than electrical.

[Mamigacz]

Wow! weird stuff going on.

I can't think of anything (besides belts) that would cause a squeal.

Before focusing on the backfiring again. It would be good to find out why you don't have spark. When you turn the ignition on, is there power (12v) to the coil? I'm assuming it has three wires to it:

power
tackometer
ground (to the distributor)

If there is no power, I think you are going to need a wiring schematic to trace the wire back to where the current is being blocked.

[davebuc]

Lewy2001 over on CCF suggested I run through this step by step worksheet. Here are the steps and the results for them. I didn't know how to do the resistance tests or where my distributor ground wire was.

TFI Worksheet. EEC-IV Systems--Typical

1. Voltage at positive Coil. 12 V desired: Actual was 12.5 V

2. Voltage at negative coil (gray & green wires) 12 V desired: Actual was 12.5 V
Tests 1 &2 performed with ignition key on

3. Using a testlite @ negative coil, crank engine, watch that the test like flickers OK. If it does not flicker, problem is indicated. Turn key OFF.

What I did was to use a multimeter, then later continuity tester light. When I cranked the engine, both the gray and green wires lowered the voltage from 12.5 to around 11. There was no pulsating in the current. It was a steady 11 on the multimeter. When I used the continuity light, it dimmed, but did not flicker.

4. Disconnect coil connector, measure primary and secondary coil resistance, also path to ground.
Primary Coil: 5.-1.5 ohms desired. Actual______
Secondary Coil 7k-15k ohms desired. Actual______
Path to Ground: infinity ohms desired. Actual________
Reconnect primary and secondary wires.

I did not know how to do #4, so I didn't do it yet.

5. Disconnect TFI module connector at distributor. with DVOM on 20 volt scale.
6. Run pin voltage. 12 V desired. Actual was 12 V
Coil pin voltage. 12 V desired. Actual was 0V
Start pin voltage-8-10 V desired. Actual was 4.45

7. Check distributor to engine block ground. 0 ohms desired. Actual______
I was not able to find the ground wire. If I find it, do I put both multimeter probes on the wire?

8. Connect TFI module to distributor ground at Pin 6. 0 Ohms desired. actual_________
Reconnect TFI module

9. Check Hall effect device output @ spout harness connector while cranking engine. desired 5-7 V actual volts: 12 V

10. If #9 is not correct, disconnect ECA and redo test at PIN 56. desired 5-7 V. Actual was 10V.
I stuck my multimeter probe into the wire coming out of the wiring harness on the ECA, with the key on, it read 11.25V, 10V when cranking.

11. If #10 is not correct, check the continuity of the blue PIP wire from pin 56. It reads 11.25 at ECA, 11.25 on the ECA side of the distributor connection

Now, the weirdest thing. All of a sudden, the 11.25V readings in #10-11 above switched to 4.5 V. I cranked the engine a few times. They switched back to 11.25 one more time, and back to 4.5 for a second time.

[davebuc]

I also substituted 2 new relay in place of both of my old ones. This did not make a difference.

Both relays have power to pin 30.

There is 12V to the posts on the back of the breakers (60amp, 15 amp, 12.5 amp)

[Mamigacz]

The spark problem sure seems related to the coil. You verified that you have power to the coil. You also verified that there was no pulsing at the negative side. I'm not sure how expensive they are, but it seems like its pointing to the coil.

Even if the coil is shot, I still wonder what caused it to fail?

[davebuc]

A strange thing happened a month ago which may be related to all this.


When I first had the engine back together and tried to start it, the positive battery cable smoldered & got hot enough to melt 3/4 of itself off of the clamp connecting it to the battery. I turned everything off, let it cool down, removed that battery & replaced it with a spare in my garage. To inspect the cable, I pulled more of the positive cable into the battery box to check it. No further evidence of melting. I put a new connector on the end of it and connected it to the spare battery.


The spare battery worked fine & I started the boat the next day.


The battery that smoldered the cable was involved in a incident before the smoldering day. When I was taking it out of the boat for the winter, I had the positive cable disconnected. When I was disconnecting the negative one, I was not paying enough attention and the wrench while locked on the negative nut, contacted the positive post. The wrench stayed on there for probably 15 seconds before I could kick it off.


I took the battery to O'Reilly auto. They evaluated it w/ their battery testing machine and said it was fine. So I installed it, which led to the smoldering incident, which almost sounds like a reverse polarity event.


Would this have messed up my ECM? Coil? Other electronics, or maybe they are all adequately shielded?


Thanks,
Dave

[LakeRats]

A power surge / issue like that can cause failures to happen, days, weeks or months later. Could be the cause of the no spark issue. I think the back firing issue is related to the rebuild. Cam timing vs spark kind of issue.

[Mamigacz]

I still think you should repalce the coil and reevaluate the igniton problem.

The cam to crank timing can be checked two ways.

The hard way:
Remove the harmonic balance, loosen the oil pan, and remove the timing chain cover. The dots on the sprockets are supposed to line up when the the engine is in #1 firing position.

The easier way, but still time consuming:

This methode requires the degree informaiton on the cam card, A dial indicator and degree wheel. The positive of this method is it will tell you if the cam is degreed properly without having to remove the timing chain cover and harmonic balancer.

Below is a copy from another forum of a half *** way to see if your off a tooth. I never tried it but it might work:

A quick little visual test is to pull the driver's valve cover and watch #1 valves as you approach TDC on overlap. Unless you have odd cam timing or a major split in duration and lift, the 2 valves should be pretty close in the amount they are open at TDC. If the exhaust valve closes before TDC the cam is way advanced, if the intake valve doesn't start to open until after TDC the cam is way retarded. This test is by no means a replacement for a degree wheel, but can be a quick visual during the initial diagnosis.

Being off a tooth will also affect compression test numbers. Excessive cam advance will show as unrealistically high compression test numbers on a big cam by closing the intake valve sooner after the piston has passed BDC

[davebuc]

I bought the Equus 3145 Code Reader over the weekend & a new ignition coil.

The code reader (in key on engine off test) read a code for "MAP sensor out of range" and had a continuous memory code for "PIP circuit (distributor sensor)."

I wondered if the sensor in the new distributor was defective, so I decided to pull it out and pop my old one back in.

The new distributor did not want to come out. After several minutes of pull and wiggling, it finally did and was missing 4 teeth on the gear that interacts with the Cam. Additionally, the hex-shaped inside of the bottom of the shaft looks shredded inside as if the distributor bound up and the oil pump kept trying to spin inside it.

I took the engine back to its re-builder so that he can find & remove all the pieces of metal, and see what damage has been done. I will also have him check the timing gear.

Rock Auto is where I bought the distributor. Part number 30-2891 which I got from CCF or PN. It is exactly the same motorcraft part number as the one that was in the boat. Rock Auto will not warranty it b/c they say it does not "cross reference" to that year boat.

Dave

[Paxdad]

Dave,
Appreciate you keeping us updated on your issue and feel for your disposition. Hopefully the engine builder will do the right thing and let you know if it was something on their end that caused the distributor to shell.

[Neverenough]

I have a stupid question. Does it idle fine and smooth with no missing or back fire? If so have you check the fuel? Is it old and stale? Bad fuel or water in the fuel can cause coughing or back fire. Just a thought.

[davebuc]

Hi neverenough,
I checked the condition of the fuel before the distributor blew up. It did not look milky / watery. (I drained the FCC) The tank sat half-full in my garage all winter, out of the boat, supported by wooden 2x4 pieces to keep it insulated from the garage floor, in hopes it would condense less. It was out of the boat for engine repair and upholstery repair. I sealed the fuel hose ports by cutting the fingers out of gloves, putting them over the openings and taping them on.

There is some question about the cam gear material and distributor gear material being incompatible. I replaced the distributor with the same Motorcraft part number. The gear on the old one looked great.

I did switch cams to a roller cam in the rebuild, so I will ask more questions with the engine builder at the machine shop.

Thanks to all for your help and support.
Dave

[Neverenough]

Depends on the cam manufacturer. Some crower cams actually have the last lobe and distributor drive gear that are cast not billet or forged. What happens is when distributor gear and cam are that hard they will eat each other up. You can buy just the gear for your distributor.I don't think that's the problem. Did the machine shop change the valve springs? Roller cams will take a heavier spring. I'm nota ford guy and know very little about fords but if this were a Chevy I'd still put fresh fuel in it and make sure that the machine shop knew what they were getting into. The cam that went in it would have to have been very close to the cam that came out. The ignition control or what ever controls the advancement of timing may be trying to over advance or retard timing due to a larger or smaller cam.