ImBatman

I know this is a very general question but I don't want to start throwing parts at this car. It is a 1990 base coupe with 76k on it. Last year I had 2 bad injectors that had to be replaced. It is throwing no codes.


When cool outside the car runs and idles better but still not great at low speeds.
When hot outside the idle is rough and sometimes hard to keep running.


In both scenarios once you get it out on the road and open it up it runs good. I run 89 octane and sometimes 93. It seems to run a little better but may just be in my head.


In an old carbureted car I would start thinking vapor lock but my understanding is this isn't possible with FI I have 40 PSI at the rail and it only drops down to about 34 when left pressurized over night. Noid test shows all injectors firing but that "could" be misleading since I got same results but had 2 bad injectors before.


Here are a few other things I replaced since I have owned it.
AC Delco Plugs
Coil
Ignition module
Fuel pump
MAP sensor




Where should I start????


Thanks!
Wade

ex-x-fire

The egr valve might be stuck open a little or it might be getting vacuum at idle, which it shouldn't. I'd try disconnecting the hose that goes to the egr and hooking up a vacuum gauge to it. Does it have vacuum at idle?

ImBatman

I Will try that this afternoon. One other thing I just thought of. I "think" I might have a leak in one of the plastic lines that goes through the firewall and supplies vacuum to the HVAC doors. Are these systems linked at all? Again I am not sure if there is a leak.


Thanks!
Wade

aklim

BAD idea. I wouldn't toss 2 old injectors. I'd toss the lot especially if they are Multec. Codes don't mean that much since they will have a reasonably wide margin before a code is tossed.

More than likely unless you have the car hooked up to a scanner and can monitor the knock counts.

It definitely is misleading. Noid light only shows current to the injectors. Same with the ohm test. Just because I knock on your door doesn't mean you are home. Best way I would think of doing it is to get a set of reman injectors that have been tested. In my case, I send them out for testing every 3 years and they usually come back with increased flow as opposed to before sending it out. All even too, within 1 or 2 cc.

With a scanner. I would take the TB off and that means you disconnect the coolant hose going in and out of the IAC housing. Connect those two together. You don't need it. Take the IAC off, spray it with a gentle mist of Brake cleaner and wipe. Do not push it in. Take the cover plate (6 torx bolts) off the top, take the IAC housing off (6 or 7 torx bolts). Clean the TB and spray the passages. Clean the IAC housing. Reassemble with fresh gaskets. I consider paper gaskets like condoms. Don't reuse either. After that we can talk about setting the base idle and checking for leaks with the scanner.

Make sure the timing is spot on at 6 and the harmonic balancer is not moving.

aklim

Hard to know if there is a leak without monitoring the IAC counts.

antfarmer2

And will add call Jon at FIC and get a new set for about the price of two. Also did you use the proper thermal grease on the ICM?

aklim

Right now I think he has 6 Multec and probably 2 Bosch. The 6 are probably spraying at different rates.

BTW, how are the wires to the plugs? Is the flame blue? Is the timing on?

ImBatman

Did not get a chance to look at it yesterday. It may not be till weekend. The wires appear to be pretty cheap brands that have been on there a while. Any suggestions on wires that I don't have to assemble?


As for the grease. I put the grease that came with the module. I used all of it and made sure I had complete coverage.


Also, in regards to your comment on the injectors flowing differently, Is there a possibility of fouled plugs even though they are fairly new? Like I said I am good at carbuerated engines but I am in new territory here.


Thanks
Wade

aklim

Most of the decent name brands are OK. You can get big thick ones but you won't see anything but a lighter wallet.

Imagine that you have 8 carbs. Do you want to replace a couple of them and leave the other 6 there without making sure the Jets are not clogged partially? I use Top Tier gas and after 3 years, I send it out to be cleaned and the flow numbers are more than before and much more even.

ImBatman

Great analogy!

aklim

What do you think the fuel injection system is? It isn't magic. Instead of depending on Bernoulli's principle and the Venturi effect, there is pressure and it is released at the right moment.

ImBatman

Ok you lost me on the "Bernoulli's principle" but I get the Venturi effect.