Need help with backfire problem

[GNRick]

I changed the coil, ignition module, MAF, cam sensor cap is tight, jiggled orange ecm wire and no problem there, positive battery cable looks good. I can drive the car for 30 miles with the occasional 10-15lbs boost with no problem, then for no reason at all (it seems) I get a backfire when in boost, under 15 lbs. I checked the spark plugs (CR43TS) which are one step cooler than stock. They have a nice whitish look to them. I thought about going one step cooler than that (CR42TS) to blacken them up a little but I wouldn't think that would be the problem. A friend suggested maybe it is the EGR valve. I looked at it and noticed I had the little hose on the wrong nipple of the EGR solenoid. Does anybody think that could cause the backfire? Any body know if it matters which nipple the hose connects to? I compared it with my other unmolested TR, that is how I knew I had it hooked up wrong.

Also, with the original MAF, when I disconnected the power to it the car idled a little higher, then when I reconnected it the car died. Does this mean the MAF was good? Maybe I should try it with my other TR and see what happens.

Thanks in advance.

 

[GNRick]

Some additional news. I switched the MAF to my other car. When I disconnected it, no change. When I connected it, the car stumbled but did not die.

Anyway, went for a drive. I watched the hood mounted fuel pressure gauge. When I gave it gas, the FP actually decreased! Went from 40 psi to 39 psi. Not a huge drop, but it should go up, not down. No knock on knock gauge. I looked at the list of mods from the prior owner. All work was done in 1994. Says it has a Hobbs ZP40-A Pressure Switch and the following:
GM 507-270 T.A. modified 2nd pump ($85.45),
RP354-3 (purple) billet dual pump coupling ($49.95),
GM 507-F pump strainer ($7.95),
ZP002-1 staged 4 wire pump harness kit ($18.95).

I would like to test the hobbs switch and the pumps. Maybe even replace the strainers on the pumps. Can anybody tell me how to do that? I think I heard that if I put a voltmeter on the hobbs switch while pumping up a vacuum line to the switch, I should see a voltage drop (or spike?) when it opens and kicks on the second pump. How should I set the voltmeter and what should I watch for? Then, if the hobbs switch works, how can I see if the pump(s) are working?

Thanks for the help!

 

[postal]

Hook the two leads of the volt meter to the two wires going to the switch. You should have full battery votage across the switch at that time (means the circuit is open). When you apply enough pressure to the switch it will close. The goes in and the goes out wire will now be internally connected and there will be no votage DIFFERENCE betwen the two so your volt meter will show 0 volts at when it closes.

IF you want to measure the voltage to ground:
1. ground one lead of the meter
2. verify you have batt votage going into the switch
3. verufy 0 volts on the goes out wire
4. apply pressure to the switch and verify that you now have batt voltage on the goes out wire.

This will show if the switch is working but does not at all mean the pump is getting the voltage. A break in the wires or connections between the switch, the pump, or the pumps ground will not show up. The best way to see if the pumps curcuit is working would be to run a jumper wire from the batter to the goes out wire of the hobbs switch. When you touch this jumper wire to battery positive you should hear the pump kick on if everything is in order. If the pump doesnt kick on the you have to start looking down stream of the hobbs switch.
check wires, both positive and ground to the pump
check for any relay that might be used
check for any fuse in the circuit

If you get to the point where you can verify the pump is getting power and has a good ground but still wont kick on then replace the pump.

If you're confused drive the car over to where I work one evening this week and I'll check it out for you.

Jason
309-253-6124

 

[1BUICKGN]

fuel filter

have you ever changed the fuel filter? this may be a stupid question but i have had this problem with a fuel filter before.

 

[GNRick]

have you ever changed the fuel filter? this may be a stupid question but i have had this problem with a fuel filter before.

WOW!!!! You must be psychic!!! I just got done looking at the fuel filter. It has probably been on there since 1994. It's a WIX screw on type, looks like a small oil filter. I checked the WIX website and found some dealers nearby. I'll call them tomorrow and see if they carry or can order the one I need. Maybe I'll start using their oil filters too. Thanks for the suggestion!

 

[1BUICKGN]

backfire

it would be nice if this solves the problem.i had the exact same problem you had and i changed the filter about 5000 miles before the problem and i ruled it out and went straight for the fuel pump.i was only using the original stock pump at the time and i am sure i would of upgaded sooner or later.