Any suggestions: MY 88 cuts out at above 1800rpm.....

[Bilt4speed408]

Hey guys my best bud nees some help. Were stumped. . He has a 90 lx . Mass air conversion. Car has worked gt-40 (cast), "B" cam, 1.7 roller rockers, long tubes, 65mm tb, 75 mm mass air, explorer intakes ported and polished. Heres the deal. Car was running perfect. Only thing was the the idle air sensor was never tapped into the explorer (gt40) lower intake. So for quick fix jsut to get the sensor into the engine so was getting accurate reading we took off the top intake and tapped it to for the sensor. While putting teh intake back on his little boy (who jsut wanted to help) was handing him the bolts. One of teh bolts had a washer on it and it fell off and you can guess where it went. In the lower intake. So he tried to fish it out with the magnet and couldnt get it. So he took off the lower intake and the washer has went into the head. then he took of teh head and there the washer was sitting on the piston. now the engine was never fired r cranked at this point. he put new head gasket on, new lower intakes i help him clean everything and it wnet back on text book perfect. everything went back on as should be. We plugged the new sensor in as well. She fired perfectly on teh first tried and idles great as always. We let it warm up and then were gonna driver here up the road. upon giving it the gas it would break up at about 1800 and get worse as you turned it up more. Often sounding like it was trying to backfire or kick back. it would run but above bout 1800 to 2000 it was very sluggish. we unplugged the new sensor and still no change. We sapped every snesor on teh engine, tried new TPS, new tb, new mass air (stock), and even new computer. We are stumped. We marked the distributor when we took it out and put it back in dead on the line we took it out at. Car was never turned over or bumped while motor as aprt as to not disturb the timing set or the fact it has a washer inside it. So my question what could cause this. Idles and cranks perfectly but above 1800 to 2000 it is like someone is choking it to death. You can hear it kcik back a little when u rev it up, not a big bang backfire but liek it is kciking back and doestn want to take the gas at all. Car has long tubes and we replaced both header gaskets as well. Also checked the sensores on teh longtubes. We also tore it back down and made sure head gasket was on right. Everything was perfect and set to factory settings and torque. I am at a loss. I know usally most of teh time a sensor goes out the idiot light wil come on and make the car run a little dif but not this drastic of a change. Any idea guys. We have tried everything we know to do. he is ready to sell here at this point. It has to be something simple we are overlooking. I have built supercharged engines and never had one kcik my butt like this. please help

 

[bill302]

same thing happened to me but the check engine light illuminated on mine and i noticed my evp sensor wire harness was not connected. the evp is mounted on top of the egr valve, i connected it and it ran great...might want to check that...also check for vacuum leaks...

 

[Bilt4speed408]

Hey Bill. It actually had a egr delete plate on it alrady. The plug is still there and it was jsut left hanging as before. I have heard you can put a resistor in it to give it a reading to keep it from acting up. i did plug a egr into it jsut to let it get a reading but it isnt mounted in the throttle body. It is jsut sitting in the back corner at this point. As for vacuum leaks I have checked everythng 5 times can't find anything that isnt hooked up.

 

[dragnazz5.0]

sounds like a timing issue or a firing order issue. i know you marked it and everything but i would just recheck it to be sure.

 

[BlownFiveLiter]

+1
Throw a timing light on it just to be sure. If the timing is off too much in either direction, you can have the same issues you're having. If you took it down to the block but reused the same gaskets that were already torqued once, that would definitely cause some major headaches. If everything appears in order, start searching for vacuum leaks, particularly the intake gaskets. Those things just love to shift when you drop the lower in place.

 

[Bilt4speed408]

Thanks guys. Gonna recheck timing for sure. ITs gotta be something simple. Everything else we have checked. We put all new gaskets and only used Felpro's. Used arp head bolts new out the box. Will try to find any lower intake leaks and play with timing too. Thanks for ur guys input