i had a nice backfire a week or so ago and i replaced the throttle body which was the only thing that appeared to be damaged (i have a Venom manifold and it took the blast). The only thing is when i fired the car up again and took it out it runs like crap. It is so lean and when i give it fuel it jsut dont want to go. The car idles identical as it did but the power is jsut not there. To put it into retrospect my car last on our dyno put down a near 340 whp @ 17 psi and with nothing changed my buddys Greddy turbocharged 1.6 Del Sol is keeping up with me with 6 psi. Thats how bad it is. CAn a backfire possibly break a map sensor or cause and mechanical problems like jumping hte timing belt. I have cheeked the car out over and over and nothing seems out of place other than the fact that its slow. If anyone has any ideas please clue me in.

 

check the injectors....

you can blow out the solenoids in them...

also, check all the sensors of the manifold...

a backfire can melt any sensors...

 

have you done a compression check, leakdown test?

 

also check that no chunks of metal got sucked into the engine...

could be jammed between the seat and valve.

 

What kind of internals do you have? And are you still on stock sleeves?

I'm betting your compression results will be in the teens.

 

The motor is pretty well built although i cant find the compression tester right now, its in my messy garage somewhere. Its an 85mm GE sleeved block, 9.8:1 JE pistons, Crower rods, Z10 girdle, everything balanced. The backfire actually happened by one of my friends. He had some nitrous in the manifold when it was off for some reason or another and he started. It cranked a few seconds and then kaboom. My map reads fine at idle and when the car is off and all the sensors are reading normal also. the car will idle but it will pop and not accelete when you rev it up and get under boost. Inside the manifold its a little black right near the throttle plate but no fragments that i can find. ill have to find my tester to give you guys a better understanding of what is going on. i have nothign to do the rest of the day so ill try to locate it this afternoon.

 

hmmm nitrous w/out fuel.. = holes in things or bent thinga-ma-bobs


i agree with the compression test... and go from there..

 

Well i didi a compression test and theres good and theres bad.

GOOD: all the cylinders are equal

BAD: they are all 120

Well i guess ill be installing new rings in this weekend. I did the test with the engine completely cold thats the correct way right. After the low results i did a wet test and they all went up to 215-220. i wasnt sure if the motor has to be cold or warm because the cars been sitting for a few days and walls might be really dry. Hurry up and reply so i can over night some rings if i need to. Also where do you get some more o-ring material or can you reuse the stuff?

 

your engine should be at operating temp. and if you suspect it is the rings you squart oil in the combustion chamber. after the oil in squrted you do another check, if the compression went up then it is your rings.

 

340 whp @ 17 psi from a 9.8:1 85mm block - that leads me to believe the rings were on their way out already - before the backfire - and that just ended it...

 

dont be surprised if pieces of piston come out with the rings...hehe.. mine did. LOL

 

Change the MAP Sensor...

 

i probably will. I want to do another test correctly since i didnt warm up the engine at all. Im sure it will go up a good bit. The motor only has like 800 miles on it so i cant see why they would go bad. This is the first motor that i have built that i even gave a break in period. Last years motor i finished rebuilding the motor friday night and i was racing saturday morning. ill call GM and get a new map hopefully they have it in stock.

 

That happened to my friend at the track, no more nos for him

http://www.geocities.com/zakynthos99/fast.MP3


[Modified by Racing Hartless, 7:48 PM 7/11/2002]

 

Well i got around to doing the test at operating temp and the results are as follows:

1 2 3 4
DRY 175 160 165 155

WET 320 300 300 310


They all seem far too low to me considering when i first built the motor they were all between 190-210 with freshly honed cylinder walls. I guess ill order a new set of rings and throw them in.

 

what kinda valves u got

 

you should get the pistons magnaflxed just in case there are cracks you don't see

 

They are Ferrea 1mm over on the intake and the exhaust. Well i talked to Race Engineering cause we buy all our pistons and rods from them and had a very indepth conversation with them since we are very familiar with one another. They stated several important things.

1. i have custom cams and they jsut might be letting some of the compression out, ill loosen up the cam caps some and do another test tomorrow

2. The motor has been driven on synthetic oil since about 150 miles and with 800 miles total nearly all have been highway miles. The rings may not be seated fully yet. Hence put in conventional and jsut drive it.

3. My ignition timing is way too retarded (me and my conservative tuning)

4. The motor does not smoke at all and uses absolutly no oil. How could the rings be bad.

5. They told me that my compression numbers are about right. i know the manual states more but he is very knowedgable and i doubt he would lead a good customer in the wrong direction

6. The map took a good blow during the backfire soi replaced the map just to make sure its not that

I think the motor is fine just way out of tune again so ill keep you guys posted. i built the block myself and i know for a fact the clearances are absolutly perfect so i have a hard time beleiving that the rings are shot. I built this one identically to dozens of customers cars and they are running great and making tons of power. We have several making over 400 whp and they are built the same way. Ill jsut keep trying to convince myself and keep my fingers crossed.