I have a problem and would like your input. I just finished replacing the HG's, heads and turbo on my XT. I also replaced all other seals while I was in there. The heads were milled prior to installation.

 

I runs rough and has a slight stumble under constant throttle. Ignition is at 20degrees BTDC. Fresh gas. Cam belts are lined up properly. I replaced the following before and after the "rebuilt".

 

Swapped MAF and TPS

Cleaned injectors (ultrasonic)

New plugs, wires, cap and rotor

New fuel filter

Cleaned connectors for the coolant sensor

and much much more I can't remember for the moment

 

Please help me get this thing fixed as it's turning me crazy.

The first thing I would do is put a vacuum gauge on it to narrow it down between a mechanical problem with your valvetrain/compression or an electrical/ignition problem. A bouncing needle when rough/missing indicates a problem with the valvetrain/compression. It helps to put a long enough hose on the gauge so you can monitor it while driving too.

 

PS Since you have a turbo, a vacuum/boost gauge on the dash could prove useful.

Thanks for the quick reply

 

I already have a vacuum/boost gauge dash mounted and under load and constant cruise its stays still, at idle it will vibrate slightly. This leads me to believe there is no mechanical problem, the engine also sounds very good and revs good, albeit with a stumble/miss.

Do you have egr, and if so, have you tried it with the vacuum hose plugged off? Try cleaning the carbon out of the valve too?

Wonder if there is some way the ignition timing could be moving around on you?

Sorry I forgot to mention, the EGR vacuum hose is plugged, do I also have to plug the port into the manifold?

 

John, I checked the ignition timing with a timing light and it's rock solid at 20 degrees BTDC.

 

I'm going to swap the igniter and coil today, check the brake booster for a vacuum leak and re-recheck ignition and cambelts.

I would guess it's ignition related.

 

Coil?

Distributor (has the crank angle sensor in it)?

 

What was the "TPS wiring" you mentioned before?

I just replaced the coil and iginiter, seemed to do something, but hasn't solved the problem entirely. I also had to reset the time because with this coil it suddenly was a 15 degrees BTDC? It's at 22-25 degrees now and varies slightly, maybe 1 degree either way.

 

The CAS is inside the distributor, but I have no way of swapping/testing that. I have a spare distributor with CAS but the plug is different. Looks like my car is an oddball. No error codes though.

joost - typically you can just swap the plug as an assembly. the entire plug w/wire will bolt up under the distributor. unbolt those and swap it with the plug from yours. it should be a bolt on affair, but i don't know what disty your spare is from? give it a look, it should swap.

have you checked/swapped the FPR? if you can't find one, i can send you one.

I will have a look at the CAS, the spare distributor I have laying around is from an automatic EA82T out of an '89 XT. Mine is a manual october '87 (according to the VIN, first sell date is june '88).

 

I also have a spare FPR, but is there any way to test this before swapping it? As swapping the FPR on a spider intake engine is mayor pain in the you know what and I don't want to do it twice.