Guys, sorry for the french...I had a stumbling and terrible backfiring motor at load (last thanksgiving), the main pump making a growling sound. Pre-pump right? Replaced that, still growling main pump. OK, the pump's got 140K on it, just get a new one. Did that. Still growling...decided to upgrade the pre-pump (from IPD). That solved the growl. In the mean time the relay was fried. Got a replacement... Started right up, ran better for a few miles about 100, still not quite right tho, good enough for the college kid. Brought the car home last week, died in driveway. Fuel pump relay dead, noticed it was getting warmish. Someone suggested the hesitation was the injectors, so I sprang for 4 new ones. I'm sitting here 2 fuel pumps, 4 injectors, 2 fuel pump relays later. Car won't start even if I jump the pumps. Plugs are fouling, clean them up, get a sputter, and then nothing. The pumps both work with a direct wire. What is this backfiring?? It is thru the exhaust. Checked t.belt. New wires, cap, rotor. Timing on 12%. Compression is good on all 4 cylinders. Please somebody, give me direction here. I don't have a shop to take it to, nobody know kjets around here. I'm out of $ throwing parts at it.
Please stop me from pulling parts of my other running bricks!!!!!!!!!!!!

Thanks so much for the good advice! I very well could have several problems.
The wiring harness is a "replacement" one volvo made and has been on the motor for several years, but I will take a look at it carefully. I have gone over all ground points one, by one, and inspected the vac hoses several times, thinking of them first off, when all this started happening. What's the best way to check the distributor? Bentley doesn't have too much info there??????

Check of the distributor! It's hard to do a really good check when it's not turning. The best check may be to install it into a running engine but here's a couple.

The trigger coil resistance can be measured at the connector on the distributor and, to test the harness, at the module connector. This has been discussed before so should be in archives.

For a static check of the timing, turn the engine to the firing point for #1. With the marks at 12 BTDC, or whatever your engine requires, check that the four metal fingers in the distributor are lined up and the rotor is pointing right at #1. I think the gap between the fingers is spec'd at .016".

Seems like you've been taking advice for a while and also troubleshooting by substitution. Welll here's some more. Instead, and you may have done a lot of this already, give this data.

Is there spark to each plug?
The ignition timing is correct, ok. (How do you check this if the engine doesn't start?)
Compression is good, ok.
All the timing marks line up, ok.
Check the entire intake system for vacuum leaks.
Does the air meter move freely? (There should be no resistance with the pumps off but some with the pumps on, engine off.)
Is the start injector working?
Is there fuel coming out of each injector? (With the pumps on, engine off, the injectors should not spray until you lift the air meter.)

hi there on my 85 244 turbo i had backfiring above 40 mph. the whole car would lose all power for about one second, then get power back, then boom big backfire. seemed to me like it was loading up with fuel. and i dont have the experience the others have given you. but i had other running problems too. strange ones. the wiring harness i put in last week seems to have made all the problems go away. it had bare wires through 98 percent of the harness. cant believe it ran at all. this is just my experience. good luck

You're absolutley right, too much fuel can do it too. He probably has this problem too. The frequency valve and the warm up regulator tend to be the culprits with the too rich problem, and of course the swiss cheese wiring harness helps nothing.

Chris

Your fuse panel is nice, new fuses, all contacts clean? Your wiring harness is new? or resembles swiss cheese? You say the relay is dead, yet the plugs are fouled? The plugs have to have been fouled before the relay was dead. You have to have spark before you have fuel. You could very much have more than one problem. The ignition signal is sent to the fuel injection relay. Your relay contains both the "system" relay, and the "fuel pump" relay...it's basically two relays in one. The relay also has an eletrical circuit in it that provides the ground to the fuel pump relay section when the ignition signal is delivered. This ground then turns on the fuel pump relay portion, which will then supply current from the fuse to the pumps. You either have another dead fuel pump relay, or you have lost spark. Check for spark at the coil. Check to be sure the ground at the windshield washer bracket is secure. Check all connectors at the distributor, the coil, and the connectors directly under the wiper motor in the passenger side of the engine compartment. Then recheck for spark.

Backfiring is usually related to the timing being off, your distributor has a weak link in the form of a star wheel lock pin, they will sometimes break and then the star wheel will kinda find it's own way, slipping around the shaft and then the timing will be off. The marks on the belt will be dead on, but the timing will be off. The replacement pin is better. You can also have a loose sleeve in the star wheel...same problem. The coil will spark at a time when the rotor isn't aligned with the cap electrodes. But this is of course when the car is running badly, not when it is not running at all.

There aren't too many components in the ignition system...the switch, the computer, the distributor, and the coil. I guess we can discuss how to check each if playing with the fuse box, grounds, and connectors doesn't solve the spark dilemma (if you have a spark dilemma and not a dead relay).

backfire in the exhaust is usually too much fuel or poor ignition or timing. pull the boot off the airflow meter and see if the clip under the flap is not broken. if it's intercooled, check all the hoses between the turbo and the intake. otherwise, you need a set of gauges for the fuel system and a good look at the ignition system, including the coil. good luck, chuck.

Frying fuel pump relays? Check the crimps on the relay socket. Or the old main pump drew so much it helped the relays to an early death.
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Art Benstein near Baltimore