BP compression Test results.....

Typhoonk · Post by **Typhoonk** » February 21st, 2005, 12:48 am

As with a lot of the mazda B series engines, I get a random rough idle, that gets worse the warmer the engine gets.
Well I just did a compression test on my engine.
RESULTS:-> 160, 153,155,155

From what I've found these are good results.
I've also cleaned and put a new gasket on the throttlebody and Idle control valve.
Got new wires, plugs, distributor cap, rotor......

Right now I'm thinking my exhaust valves are leaking when the engine warms up. Anybody have any other ideas?

Tunes67 · Post by **Tunes67** » February 21st, 2005, 1:14 am

Your results are likely too high for it to be a valve issue.. too even as well.. pretty typical of a used broken in engine. If you had a valve sealing issue you would have very low compression in one or more cylinders. My compression test was 183, 181, 40, 180. The burned valve was in the "40" cylinder. So thats good news for you. I have a vibration issue that looks to be a result of worn motor mount bushings.. I think the rough Idle that was present likely for the last 20k miles of my engine pretty much trashed the motor mount bushings. Have you checked your distributor shaft for excessive play? Do you get any hesistation in addition to the rough idle?

Tunes67

Typhoonk · Post by **Typhoonk** » February 21st, 2005, 2:46 am

I get slight hesitation when I'm at WOT when accelerating onto a hightway. Nothing too big, the only thing is when the car is hot after about 15min of driving - the idle is ok till I have a load on it. Turn the fan on, and the idle searches for 20seconds then goes to normal. But sometimes it just idles at 500rpm (very random).
But how would I check my distributor for 'play'? cause I just had it removed and put back on for a bad seal that was around it. Now it doesn't leak oil.

I'm about due for spark plug wires. So tonight when I did the compression test, I regapped the spark pluggs and checked them. They all look the same, and look in really good shape.

Also I have an air/fuel gauge. And whenever it idles at 500rpm or goes low for a bit, my gauge shows a really low lean condition. Should I check my injectors? or my throttle position sensor?

Tunes67 · Post by **Tunes67** » February 21st, 2005, 10:37 am

To check for excessive play or movement of the shaft in the distributor housing you will need to remove the distributor to get the best results. After you have the distributor out take the cap & rotor off and grab the end of the shaft where the rotor seats.. try wiggling it left to right & up and down. If the shaft does more than just spin freely in the housing.. you have play in the shaft.. this means your rotor could be jumping around inside your cap and your spark would have intermittant fits of weirdness.. like hesitation or uneven idle. Dont grab the shaft by the bottom to check though, it has a little gear on the end that is held in place by a single pin and is designed to move a bit (at first it confused me into thinking I had play in my distributor shaft, but in the end the shaft was nice & tight and spun smooth in the housing) Hope this helps.

Definately check your injectors, also if you have a lean burn condition it could be a result of a malfuntioning O2 Sensor. You should correct this soon as a lean mixture condition can cause a valve to burn.

Tunes67

Tunes67 · Post by **Tunes67** » February 21st, 2005, 10:49 am

When you have your injectors tested.. (I dont know what unit of measurement the shop used to indicate flow level unfortunately) Normal injectors flow at about 100. When I had mine flow checked I got back 64,91,94,96. And the spray pattern was off on 2 of my 4 as well (this is caused by fuel & carbon buildup that blocks the injector screen/filter thingie (dunno what its called). After they were rebuild mine flow 100 across the board with normal spray patterns. Most shops will flow check your injectors for about $35 USD. Complete test & rebuild for my 4 injectors was $130 USD.

Tunes67

Typhoonk · Post by **Typhoonk** » February 21st, 2005, 1:05 pm

That injector thing sounds like an idea. And I will also check the movement in the rotor of the distributor.

Definetely cheaper then getting a head rebuilt if thats all it is!!! Here's to hoping!!!! cheers!!!

Tunes67 · Post by **Tunes67** » February 21st, 2005, 1:22 pm

This is a pretty nifty little tool I picked up to check for consistant spark on each plug wire while the engine is running. You can use a timing light to do the same sort of thing.. but this is cheap and you can adjust its sensitivity.. pretty cool little toy

http://doityourself.com/store/1796457.htm

Tunes67

Typhoonk · Post by **Typhoonk** » February 21st, 2005, 3:02 pm

how do you use it?

Typhoonk · Post by **Typhoonk** » February 21st, 2005, 3:03 pm

how do you use it?

Tunes67 · Post by **Tunes67** » February 21st, 2005, 3:08 pm

Pop the batteries into it.. turn it on.. adjust the sensitivity knob and put it on top of your plug wire.. as close to the spark plug as possible. See the whitish area along the handle? It flashes red with each spark pulse it detects going through your plug wire. You can adjust the sensitivity so that you can even determine which plug wire has the hottest spark pulse (and which has the weakest) Pretty nifty tool to help track down misfires and plug wire arcing / grounding.

Tunes67

LongJohn · Post by **LongJohn** » February 24th, 2005, 8:57 pm

When I put my BP in, I sanded all the ground lugs, and added a few key ground wires of my own. My idle is perfect. I can turn lights on and off, turn the radio on and off, roll the window up and down, turn the AC on and off, and the idle doesn't change in the least. All of these things would whack the idle on my old SOHC.

Bad grounding = bad sensor signals back to the ECU. Also, the resistance of corroded terminals will go up at higher temps.

As far as WOT is concerned. I get only the smallest hesitation when I punch it. This is because the flapper in the VAF takes a moment to open. There is nothing you can do about it. If you have worse than normal hesitation, it could be a variety of things, but grounding can also cause it.

Do this:

1. Run the car until it is hot and idling poorly.
2. Turn on the headlights and stereo, turn on the dome lights, etc.
3. Use a volt meter and see how many millivolts you see between the chassis and the battery terminal.

You should see around 30mv, perhaps 50mv. If you see several hundred mv or worse, your grounds are problematic.

I know, I harp alot about the grounding, but it is easy to check and bad grounding can cause all kinds of irratic behavior.

johnboi85 · Post by **johnboi85** » February 24th, 2005, 10:52 pm

i would get a new iac valve. that solved my problem. if you had a/c your idle would actually just cut out.

Ateana · Post by **Ateana** » April 28th, 2005, 11:41 pm

Tunes67 wrote:This is a pretty nifty little tool I picked up to check for consistant spark on each plug wire while the engine is running. You can use a timing light to do the same sort of thing.. but this is cheap and you can adjust its sensitivity.. pretty cool little toy

http://doityourself.com/store/1796457.htm

Tunes67

thats just an electrical tester.. home depot or rona 10 bucks you use them to check if recepticles have voltage....

Tunes67 · Post by **Tunes67** » April 29th, 2005, 12:05 am

Actually.. its not.. its an inductive tool.. no electrical connection required for it to do its job. Works on the same principle as inductive timing lights. The reason I like it is because its sensitivity is adjustable.. so you can get an idea of how strong the spark through a given plug wire is.. can even adjust it based off of the length and resistance of a given plug wire. Cheap decent little tool.

Tunes67

Ateana · Post by **Ateana** » April 29th, 2005, 6:16 am

trust i carry one at work and use it to see if wires are live and your right there is no connection required