Soonerguy210

Hey guys I'm having problems with my 89 lx. Lately it started misfiring and backfiring through the intake. I've replaced the plugs and wires, fuel filter, iac, maf and distributer but the problem hasn't went away. It's real bad when going up a hill, I lose like 10 mph even while accelerating. It feels like it's really struggling, almost like it's pulling a trailer or something.
A little bit about it and some recent history. It's got Edelbrock performer heads and intake, scorpion roller rockers, the timing chain has been replaced before I bought it, and it's only at 115xxx miles. Recently I had to replace the valve springs bc one broke, but it was running fine after that until recently. Any ideas? Thanks

wbrockstar

Run codes to see if any are present.A jumper wire & your check engine light is all thats needed.
http://sbftech.com/index.php/topic,2471.0.html

You also need to run a fuel pressure test.You can rent a test kit at Autozone.
Key On/Engine Off= 35-45psi
Key On/Engine Running= 30-45psi

Does the backfiring occur when the engine is cold and hot or only at one of those temps??
The tps should be tested too.
http://sbftech.com/index.php/topic,29736.0.html

Soonerguy210

I have a fuel pressure gauge under the hood that shows 38. Tps sensor was checked and adjusted to where it was supposed to be when I replaced the maf and iac about a month ago. The check engine light isn't coming on, and it acts up pretty much anytime but I feel like it's worse after it's warmed up

wbrockstar

(CODES) There are numerous codes that wont even cause the cel to come on and there are others that only cause the cel to come on during the time when the failure is actively occuring,so the absence of a cel doesnt mean youre code free.

(VACUUM LEAKS) When a vacuum leak occurs,the air drawn in is considered unmetered air since it didnt get accounted for by the maf sensor.It will cause an excess amount of oxygen to enter the exhaust,
triggering the o2 sensor(s) to read lean which will then trigger the ecm to (falsely); richen the fuel mi​xture.See if youve got any vacuum leaks.The intake gasket,egr valve diaphram & the purge valve/charcoal canister hoses are common leak points.
D
(EVAP PURGE VALVE) Make sure the purge valve isnt stuck open.To check it,just disconnect its vacuum hose from the charcoal canister,plug the hose,leave the canister port open then take the car for a test drive.If the backfiring disappears,the purge valve is likely stuck open.If it sticks open,it triggers the o2 sensors to read rich,which will trigger the ecm to lean the fuel mixture.This could lead to backfiring.

(EGR) When the egr valve is open,it causes cooler combustion chamber temps which allows the ecm to lean the fuel mixture and add timing advance.If the egr valve is leaking exhaust gases during wot or opening when its not supposed to be (should open during partial throttle/cruise mode ONLY) the lean fuel mixture and added timing advance can cause the engine to backfire.One way to check the egr valve is by removing the vacuum hose from it,plug the hose then take the car for a test drive.If the symptoms disappear,the egr valve is dirty or an egr system component is faulty.When a egr code or fault is detected,the ecm shutsdown egr function in the logic so the fuel mixture & timing advance will revert back to normal values

(FPR) Once the engine reaches operating temp,remove the vacuum hose from the fuel pressure regulator,check the inside of the hose for wet fuel and the odor of fuel & look at the regulator port to see if fuel is seeping out.If either condition above is present,the regulator is bad.

(ECT) Since it has the most affect over fuel & timing than any other sensor,test the ect sensor with a meter set on ohms.Disconnect its harness & touch the meter leads to the ect sensor terminals.Test it while the engine is cold then test it hot with the engine at operating temp.The ohms value should match the chart below for each given temp
the sensor was tested at.If the ect is out of range,reading too high of a coolant temp,it'll cause the ecm to back off fuel delivery.

Soonerguy210

So I just noticed that when it starts really acting up, after I stop, it's idling higher than usual. Instead of the usual 750ish it's up around 11-1200 range

Soonerguy210

Btw thanks for all you guys feedback. I'm going to try these steps tomorrow and let you know what happens

Soonerguy210

A few more details. My car doesn't have a smog pump, o2 sensors or egr. It hasn't since I bought it in 08. Also when I take off, if the rpms are low or makes a loud clanking noise. My brother said it sounds like a diesel. As i think of more details, I'll update the past with them

dawson1112

Well right there is your problem. Your car needs 02 sensors to regulate the fuel mixture and timing. With no 02 sensors the car has never ran properly since you've owned it then. Driving around without them the computer has been causing it to run really rich with retarded timing. Your valves are probly covered in carbon and now its detonating. Carbon heats up and causes the fuel to ignite before the plugs fire. Get the 02 sensors, and try to run some seafoam through the brake booster vacuum hose a little at a time. Its gonna smoke like crazy but you gotta clean them valves off.

wbrockstar

When the engine is started cold and until it gets up to operating temp,the ecm uses preset fuel and timing values from a table to keep the engine running (Open loop) Once
operating temp is reached, the ecm uses feedback from the o2 sensors & other sensors to control fuel & timing (Closed loop) The lack of o2's is probably causing the ecm to remain in open loop.

Soonerguy210

A few questions I'm confused about. I've had the car for 10 years and it's never had o2 sensors. It's got a dummy switch in place and until recently it's never had any issues. My brother kept telling me the roller rockers just need to be adjusted bc after the valve springs were replaced a few months back they could have come loose . So I took it apart and adjusted them but it didn't fix anything. He usually knows his stuff, I just can't get him to help me. Anyways after that didn't work I ran codes and got an 87 which says fuel pump relay failure, which makes sense bc I always felt it was a fuel delivery issue since it was running lean and really struggled under load. If this doesn't fix it, any other ideas? We've already ruled out vacuum leaks, the fuel pressure regulator, maf, iac, tps and timing. Sorry for the long post. Thanks again for any help