Engine swap - What did I screw up?

I have a 1997 Sport and to make a long satory short I blew the head gasket at high speed on an expressway and melted a piston by the time I got off the highway. Or, in other words, I trashed the engine. But with help from a friend I scored a 100k engine from a local pull and pay junkyard for $200 and swapped it in. Everything is hooked up the way it came out and the engine sounds sweet when I rev it with zero smoke or knocks.

But it will not start without giving gas and it will not idle unless I continually give it gas. It seems to get better as it warms up. Since I have two of everything and basically know everything from both sets works right I tried swapping throttle bodies and swapping the coolant sensor. It also has new plugs, new distributor cap and new rotor. And there is no check engine light or any codes that my generic scanner will pick up.

The only thing out of place is that I couldn't remember where the ground strap from the firewall connects. But it doesn't seem to matter where I bolt it in regards to this problem. And I cleaned up the engine grounds at the coil. I also see no reason to believe I have a fuel pressure problem since it was running like a scalded dog on the day of the meltdown. But something is obviously different swapping from the old motor to this one.

The "new" engine came out of a 97 Grand. But I swapped the flex plate to the one from my blown motor (they were different) and I also installed the intake manifold, throttle body and all sensors from my old motor. Ther only part I left original to the grand (except the long block itself) is the distributor. Even the water pump and oil pump are new. And I can't find any vacuum leaks. All of which exhausts my ideas about what I screwed up.

Anybody have any other suggestions?

So, you have an unknown distributor in your engine. Something wrong with the original?

Head to firewall ground, unless the GC head doesn't have the headbolt/stud in the rear, driver's side.

Just for grins and giggles check rockauto.com and see if the synch sensor for your XJ and the donor GC are the same part number.

If it won't start or run without dumping fuel then you really ought to check the pressure?

Ignition system has nothing to do with gas pedal... although the CPS/CKS could be causing a problem there.

Grreatdog said:

.... it will not start without giving gas and it will not idle unless I continually give it gas....

Click to expand...

That is the usually the result of the ECU re-booting and deleting the idle settings. Letting the battery run down, disconnecting the battery for an extended period of time, or a failing battery will re-boot the ECU. The engine will not start unless you pump the gas and the engine will have a very low idle and stall.

Start the engine and drive for 10 minutes. The ECU will re-learn and the next start should be normal.

If you experience these symptoms over and over, load test the battery. In your case, check that all the ground wires are properly connected.

If it runs fine other wise but won't start/idle without just a little bit of throttle, your IAC (Idle Air Control) motor is bad, little sensor on the side of the throttle body that lets air bypass the throttle blade to keep the engine running. If you close the throttle 100% the engine gets no air so it stalls, if your IAC isn't working to open and close according to load (ac on, high amp draw, turning the wheels at idle etc) it will stall. I'd swap your old known good sensor out first, or hell just swap the whole throttle body out it's only 4 bolts, I think there's 4 holding the IAC on.

Dweezel

[edit] Seems to 'get better' or runs fine? explain Gets better? is it less likely to stall when it gets warm or just stumbles?

joe_peters said:

So, you have an unknown distributor in your engine. Something wrong with the original?

Head to firewall ground, unless the GC head doesn't have the headbolt/stud in the rear, driver's side.

Just for grins and giggles check rockauto.com and see if the synch sensor for your XJ and the donor GC are the same part number.

Click to expand...

This rang true. I have already swapped all the sensors and throttle body around plus I have no reason to suspect fuel pressure. But the distributor that I left in the motor was from a GC with a different flex plate, transmission, etc. So the pulse ring and all could very well be different.

So I swapped out the GC distributor for my old one this morning. I went through the whole reinstall procedure to make sure it was right. Bottom line: it fired the instant I turned the key, it is running on all cylinders and idling perfectly. Sometimes you just need a brain reboot after staring in the engine bay too long.

So thanks for the dope slap J_P. Project ghetto repower is now finished. I even managed to come in under my self imposed $500 budget. I spent $200 on the motor plus a new oil pump, water pump, oil pan gasket and exhaust manifold. And the welder charged me $35 to weld up my cracked header.

Time to take the old girl for a spin.

probably the cam sensor in the distributor

Everything checks out fine after the shakedown run. I rolled the dice buying that $200 pull and pay motor (we did at least check run the VIN on the junker to get an idea of the mileage) and it paid off.

Glad you got it! arty:

Sometimes it is the simplest of things.