Hi guys,

 

Well i'm sure some of you remember some of my frantic attempts to get some readings off a std injector (cica 1989/1990) but i have another question, i know what they

read if they are working correctly and i know what they read when they are dead, but which is best....fi no no to much harry hill, now my question is what state are they in if they read 140 and dropping.... i will say that this injector is still working.

 

Thanks

 

Rich

Are you talking about the resistance value in ohms? if so an un-powered injector should be around 14 ohms, have seen them go both lower and higher resistance and of course open circuit, anything more than 2 ohms either way is a no no.

 

Jeff

Thanks Jeff, so if its still firing it wont be for long...so better change it.

Thanks Jeff, so if its still firing it wont be for long...so better change it.

 

Yeh, any change in the specified resistance is an indicator of a problem with the coil winding connection inside the injector, what can happen is the injector still works in a fashion but the response time will be all over the place, and can actually feel like a misfire at certain revs / loads.

 

I always used an old injector connector with fly leads on and you can connect to a battery then and do a repeat on off connection and see how loud the click is and how rapid its sounds, all in connection with a good resistance value, in fact that method of an injector connector and fly leads is really useful when on the engine as you can do a quick check for click on each injector without removing them.

 

Jeff

Thats a good idea Jeff, i can see all those years under a Zed didn't go to waste.... respect. Just a quickie, followed your link to zedworld, ended up on the detonation page, first 2 graphics explain normal and preignition, but although the third graphic is about detonation, it doesn't actually say what causes it. do you mind giving me a little explanation, i know its off topic, but its my topic...

 

Thanks

 

rich

Thats a good idea Jeff, i can see all those years under a Zed didn't go to waste.... respect. Just a quickie, followed your link to zedworld, ended up on the detonation page, first 2 graphics explain normal and preignition, but although the third graphic is about detonation, it doesn't actually say what causes it. do you mind giving me a little explanation, i know its off topic, but its my topic...

 

Thanks

 

rich

 

Yes no probs, firstly the sketches and explanations are reasonably accurate but are lacking in content so lets just fill some of it in and hopefully will be clearer

 

 

 

 

 

"Pinking" "pre-ignition" " detonation" are among some of the terms that loosely all relate to the same thing, that been incorrect ignition of the fuel / air charge but have different connotations of course. Pinking reference is mostly heard from engines under load with advanced timing issue, this also can be caused by a weak mixture and was a feature of many early eighties cars that were been forced to run on ancient carbs with way too weak a mixture as manufacturers were then under pressure to increase mpg on cars and as direct fuel injection tech was not freely available at that time.

 

Pre-ignition is a case of the air / fuel charge been ignited too early by foreign bodies such as hot carbon deposits in and around the valves, this usually happens just prior to the max compression been attained, the flame front will start to grow too early with piston not yet at the top of the cylinder the charge then expands rapidly as the piston is still not completed its full movement upwards, this is a negative explosion of course and loads the piston, rod and crank with unwanted shudder force against its travel, however the mass of the engine forces against it, and then the correct spark occurs, but the charge is already 50% to 80% or more ignited. That leaves the power stroke down compromised, with the charge not having its full content, engine`s suffering pre-ignition will be down on power of course and the poor burn will actually be dirty in nature and will add more carbon deposits to the charge area, actually making it worse. if left unchecked the engine will suffer serious damage.

 

Detonation, is in turbo cars a major cause of damage, the ignition spark is correct, and the flame front will develop in the initial stage as it is expected to, however the amount of boost ratio against the air/ fuel charge is essential to be correct or the boost level will suppress the flame front, the addition pressurisation caused by the boost will develop a second flame front, this split in the flame front has a real chance of causing hot burn damage to piston tops.

Non turbo cars can of course be described as having detonation issues, but that is more to do with compression values and mismatched air / fuel charge and poor chemical reactions during combustion leading to excess heat.

 

The problem with the terms been somewhat ambiguous is that misunderstanding of the differences is bound to happen, when we all hear of engine`s going bang after a build and boost increase its easy to blame a bad build or bad map, and yes whilst there is of course a connection, what actually goes on in the cylinders is complex and when we know manufactures get it wrong some times its no wonder after market builds and tunes need to be planned out.

 

That is why trusted methods will proven results along with a good builder is essential, basically any big builds thinking should start right at that point where the piston is about to reach top dead centre and ignite the air / flame charge, get that right first, then build backwards through the engine to the turbo`s, intake and exhaust, each step maintaining that original start point where the charge is correctly ignited. This will ensure your boosted engine will all work together, I do shudder when at the start of a build, the owner will be discussing exhausts and turbo choices as the main criteria to getting those magic numbers.... no, no, no, think last first and work backwards.

 

 

Hope that helps

 

Jeff

 

Google search bits

 

Knocking should not be confused with pre-ignition – they are two separate events.

 

Pressure and temperature are strongly linked, knock can also be attenuated by controlling peak combustion chamber temperatures by compression ratio reduction, exhaust gas recirculation, appropriate calibration of the engine's ignition timing schedule, and careful design of the engine's combustion chambers and cooling system as well as controlling the initial air intake temperature.

Edited November 6, 20178 yr by JeffTT

Jeff, wow! thats really really useful and interesting. i appreciate it. i think that post deserves to be on the sites FAQ etc page..

 

Rich