Can repair shops and dealships do a diagnostic scan that will bring to light problems with the emissions system that are not setting codes? For instance, if the MAF isn't working properly, but is not setting a code, can they plug in a machine that will tell them this? If they can do this, where can you go to get it done, and how much does it generally cost?

 

you have to find somewhere that'll do it for your ride, but mos tplaces are setup for nothing but OBD2 now, which means our cars are SOL, but some places still do it. It'll run you between 60 and 80 bucks, depending on the shop.

 

Will it actually reveal anything helpful? As to why my car is bogged down and backfiring?

 

probably. I know that when i was in school, we had an old smog test machine for the 2-speed idle test and it had a diagnostic mode that gave you A/F mixtures, spark lines, and all kinds of other junk. Man I wish I still had access to that machine. My car is doing the same thing yours is it sounds like. if I get on the gas from a stop, it bogs down, but if I get off the gas and then back on, it's fine. it also backfires once in a while.

 

Mines always bogged, except in one situation: if I give it 3/4 or more throttle say from stop, when I hit maybe 3000 or 3500 rpm, the bog disappears, it's almost like a boost. I've done a lot of work this summer, but nothing helped. The things I still need to check are TPS, valve timing (make sure the timing is what I set it at), vacuum leaks, and maybe compression. I don't know, I hope a scan will help me out.

 

don't spend the money on a test if that's all that you have left to check. Vacum leaks are easy to find, if you can't hear one, get a vacuum gauge and splice it into a ported vacuum line. I forget what line it is, but it's one of the ones that come off the TB. If you plug into one and it has little or no vacuum, then plug it into the other, you should get about 15in of vacuum at idle. if it's any lower then you have a leak somewhere. i used to have a chart that told you what different readings ment, if i can find it, i'll post a pic of it. Buy a compression tester...and a good one that actually screws into the spark plug hole, not the little chepo ones that you have to hold in. To test the TPS, there is a procedure in the haynes manual for it, also tells you how to set it, for this you need a digital Voltmeter capable of reading down to 0.50v or something like that. The Vacuum test combined with the compression test will also tell you if you have proper valve timing.

 

here's the procedure on the TPS out of the haynes manual. I didn't uses a jumper wire to connect in, i just shoved the probes into the back of the harness with it still attached to the sensor. it's not the "right" way to do it, but it works. When it talks about jumpers A and B, jumper a is the top wire (this gets the red lead from the voltmeter) and b is the middle wire (gets the black lead). Hope this helps ya' out. i'll see if I can come up with anything for the vacuum readings. Compression should be around 150psi all the way around +/- 10% i think.

 

This page is actually for a F-O-R-D F150 engine diagnosis, but you can see that all of the information came from sources regarding the general diagnosis of any engine. Hope this helps.

<A HREF=http://www.fordf150.net/howto/diagnoseengine.php>Vacuum Diagnosis Results</a>

 

OHH, thanks you very much, 2.8 boy.

Your link is all that I need for tomorrow (This week I bought a vacuum tester). My instructions say: Normal range: between 18 & 21". I'll check this weekend.



Regards,

Denis V.

 

I think normal for our cars, since they are kinda little is btween 14 and 18 depending on engine wear, someone else might be able to tell you exactly what it is. I think most people here have about 15 from what I have read.

 

Thanks for the info 2.8. I think I'll be doing some diagnostics of my own next Saturday.

 

Dude..your bogging down below 3000-3500...I had the EXACT same thing. It was flooding out...I had 2 or 3 broken fuel injectors. The car would barely out-accelerate my old V6 Camaro, then hit 3500 rpms, spin the tires and whip sideways violently.

If you havent already, check your fuel pressure!! Watch to see if it falls when you take the key back out.

 

I did check my fuel pressure not that long ago. But when someone asks you if it holds, what does that mean? Like I think it fell 10-15psi over 30minutes. Is that normal, or should it hold longer? Should it hold constant at 43psi for 5 minutes or something (we're talking engine off)? I guess for car on, it would just stay constant at 35psi or thereabouts.

 

In all honesty unless you set a code most shops diagnostic equiptment wont do anything. If the "sensor" or emmisions device is starting to fail but does not throw a code then it is still in spec and a scanner will show it is still in spec, nothing will be accomplished you will still have an intermitant problem and have less cash to fix the real problem. A scanner is a neat tool but it's nothing magical unless you consider how somthing so small can make such a large amount of money dissapear.