Generally when the engine backfires through the intake, its due to either wrong cam timing or ignition wire firing order. I have not seen any vacuum leak cause a backfire through the intake but have seen vacuum leaks as a result of a backfire. Since the car was running properly before, I would assume the firing order is proper and there were no major vacuum leaks. Do a quick compression test since its easy and won't take much time.

You probably know this, but not only do you have vac lines off the J-boot, you have them off the intake manifold/log as well. Have you checked those? And a backfire would have to pass throught the throttle to get to the J-boot, so check the throttle body and TPS as well.

If you were doing the cam gasket, maybe there's a lifter issue. But it seems unlikely given the car was running well a couple of days before this.

I pulled the J-boot and all is well with it. I checked ALL the vacuum lines even the ones under the intake manifold, brake booster. I did not see any which were off or loose.

I want to get this thing running for the weekend
Speedy:)

I measured the fuel pressure at the rail. It was about 36-38 psi. (I used a guage which went up to 160 psi)

I reassembled everything and tried starting the car. This time the wind was blowing from the back of the car so I can smell a strong gas smell from the exhaust. If I nurse the car by blipping the throttle and get the RPMs above 3000 RPMs and blip the throttle the motor revs quickly and nicely. If the RPMs fall below about 3000 RPM and I blip the throttle the motor will spit and sputter.

I am thinking it is time to remove, dissasemble and test the AFM. I am thinking the signal is pegged which is making the DME think I have a crap load of air flowing into the engine when in fact there is not. In my mind this would explain the spit and sputter at below 3000 rpm and more crisp response at higher RPMs.

So far everything else has checked out. I have not done a compression test yet though.

What else is there??????


Speedy:)

I would still check the compression before moving forward. As for the AFM, do you know how to adjust the main air/fuel mixture under the rectangular plastic cover of the AFM? That would eliminate the problem of the car running rich due to AFM calibration. I have an exhaust gas analyzer (non-dyno smog machine) but I doubt most people have that sitting in their garage for this kind of problem. Your best bet is to drive it to a smog repair place to calibrate your AFM if that is indeed the problem.

legoland951: are you referring to the calibration spring tension? IMHO there is no way a backfire would screw that up unless the fastener came out. Yes, I think speedy has an AFM problem. My AFM barn door rubbed ever so slightly when I bench tested it, but once it got hot and on a very hot day, it stuck wide open. I fixed it with emery cloth. No problems since. I also "re-tracked" the sensor wiper per FRWilk's procedure. Clarke's Garage procedure is essentially the same:

http://www.clarks-garage.com/shop-manual/elect-22.htm

did you check seals on the oil seperator? they shrink and break with time. pull off the large vaccum line thats connected to the j-boot right before the TB. blow into it and if theres no pressure building up then either one of the two seals is bad.

I just had the same exact problem as yours a couple weeks ago. It was the vaccume line going from the Idle control valve to the intake. I had to remove the intake to see the crack in the hose. I checked it many times with it on and i thoungt nothing was wrong, untill I removed the intake. You may want to pull the intake and throughly go throungh all the hoses.

OnZedge, I don't think its the AFM at all causing the backfire but if its dumping fuel out the exhaust and the car is running rich, it most likely will be the AFM calibration.

I pulled the AFM, removed the black cover over the electronics and tested the signal per clarks-garage and it checks out. There are no spikes or abnormal fluctuations in the voltage signal.

I will have to check the compression and the vacuum lines once again. i will blow in the ones suggested as well.

Speedy:(

Grrrr.

I just blew in the line closest to the TB and there is no pressure build up, I can hear a hisssss sound as I blow. I tried to smoke a cigar and blow the smoke into the hose to see where smoke came out. I could not see anything. I tried an incents stick as well but there is too much wind. I am going to try soaking the area with soapy water and see if I can make bubbles when I blow through the hose.

Speedy:)

I was able to make bubbles. On the T-connection which goes in the hole right before the TB there is a large vacuum hose. Thsi vacumm hose runs under the intake manifold and runs to a black plastic canister. The canister is located under the intake manifold between the rear intake runner and the intake runner directly in front of it. The canister looks as if it is a part of the oil fill tube. The canister looks like it goes into the engine block. It is where it enters the engine block where the leak is.

Does anybody know what this is and what it does?

How does it seal into the engine block?

Speedy:)

http://forums.pelicanparts.com/uploa...1183233654.jpg

This is a pic of the canister where the large hose goes to.




http://forums.pelicanparts.com/uploa...1183233788.jpg

Here is a pic where the canister is leaking. It is where the black plastic goes into the engine block right under where the head bolts on.


Speedy:)

You have 2 separate problems it seems. Backfiring and fuel dumping. If you have a vacuum leak, you should have a lean condition, not rich. The AFM can work perfectly and be out of adjustment at the same time causing the car to run rich so the testing you did cannot determine whether your car is running rich or not. Also, vacuum leaks cannot cause backfiring.

If you do a compression test, you can probable find out whether or not that is the problem causing backfiring

If you get to a smog station or know someone who knows how to calibrate the AFM, you can solve the problem of your car running rich.

If you do not do the most obvious things first, you may end up wasting time.

Pics way too big. Anyway that is the hose from the idle stabilization valve to the oil separator canister.
944.107.187.01
Dal

Compression numbers are as follows....

Front cylinder 165
2nd from front 165
3rd from front 165
rear cyclinder 163


Speedy:)

Another thing to check is the installation of the distributor cap. There is a slot and only goes in one way. If its installed at an angle, the rotor can hit the cap causing backfire and subsequent problems. I think the compression numbers provide conclusive evidence the cam timing was never off. Are you sure the exhaust smell rich? If you check the cap/rotor and it looks ok, I can take you through the procedures of how to adjust your AFM calibration.

I pulled the cap and rotor off for the third time and checked continuity between the coil wire and the button on the inside of the cap. OK. I pulled the wires off the cap and checked voltage with the ignition key on and I got 12V.

I pulled the large vacuum line off of the J-boot (the oil seperator line) and put tape over the hole on the J-boot to block any potential vacuum leak and started the car. There was no improvement in the car sputtering.


Upon initially starting the car without my foot on the gas the starter engages and when it fires up it revs to about 2000 RPM and then stumbles and dies all withing about a second. I wonder if the throttle position sensor is goofy.

I will see if there is a clarks-garage write up on trouble shooting the TPS.

Speedy:)

The TPS operation checks out as being OK.

Speedy:)

TPS...By hand...move the throttle cam until you hear a "click", this click should be heard almost instantly. If you turn the cam more than an inch or better it needs adjusting or replaced but set the adjustment first.

You mentioned the hoses were cracked, most likely more are cracked so check every rubber line you can find. Double check the throttle body vacuum lines, they could be switched around. These are the 2- 3mm lines usually connected to a smaller hard plastic line(stock OE).

Dal