Hello all, I have a 1988 IROC with the tuned port 350, I fixed a misfire in the engine by replacing the plugs and wires. However, the car is still pretty slow, as in it wont even chirp the tires from a stop and flooring it. My old 305 had more power. There seems to be a delay from when I give it gas to it revving by about 0.5 seconds. I checked timing which is good (4 degrees), all cylinders have good spark (checked with the light), fuel pressure is what it should be at (42 upon start and drops to 35 when running), and the air filters are K&N and clean. I replaced the MAF and TPS as they were throwing codes. There is no longer any codes but I still feel as if there is a severe lack of power. Can anyone give me ideas on what I could be missing to need to check? Thank you!

 

[controversial] The K&N filters killed your last maf. [/controversial]

Did you set the TPS after replacing it?

 

I did set it to 54 or whatever the standard was. Was a bit of a pain but it is correctly installed

 

Proper timing spec on the L98 is 6 degrees BTDC, BTW I set mine at 8 BTDC and it gave the car a little more kick.

 

I will set it tomorrow if I can, any tips on getting the distributor to come out? My distributor wrench is blocked from turning inside that small area by all the wires and whatnot in that space

 

I'm no expert by far but a few questions came to mind... You mentioned it being a "1988 IROC with the tuned port 350" then stated "My old 305 had more power." so is this a 350 swap situation? IF yes, What Injectors? Original ECM w/ 305 chip? IF No... any means of datalogging? You also mentioned doing plugs & wires, any other tune up related things like ICM, Cap, Rotor? Again, I'm no expert just attempting to help a fellow thirdgen'er.

 

Appreciate the help, old 305 was a different car. This is the original motor with 112k miles on the vehicle. I have not changed cap, rotor, ICM, or any other things. Not sure what you mean by datalogging so a no to that one

 

You don't take it out, You just loosen the bolt and turn the body of the distributor a little. Flex head ratcheting wrench or a crowsfoot on an extension should do it. Regardless, the timing being 2 degrees retarded isn't your problem. I ran mine at 4 degrees BTDC before I checked it and had significant tire destruction ability.

 

Thank you, I figured the 2 degrees off timing wasnt going to significantly loose power. Any ideas what I can check next?

 

In a no codes situation, a datalog can be helpful. Could be injectors if they're old, but I wouldn't jump to that conclusion immediately. Probably not cap and rotor but that's an easy swap that usually accompanies plugs and wires.

 

A weak spark can definitely cost significant power. Could be the ignition coil on the way out.

 

I used a test light after changing the plugs and it had pretty strong illumination, would that be affected by weak spark?

 

How could I go about checking injectors?

 

Your ignition coil was mentioned... Have you connected your Spark Checker in-line between Ignition Coil and Cap? Same strong light?

Datalogging is done via ALDL to USB cable, laptop, and TunerPro RT software. I've found it very useful.

 

About to check that, will report back in 10. Datalogging is something I will have to look into. Not sure where to begin on that one

 

Im back, the light is quick strong between the coil and cap. It threw code 42 but I wiped it and drove around for a couple minutes and it didnt come back, thought it might have been due to being unplugged to add the in line checker.

 

You can ohm them cold and hot to see if there are any outliers. That only tests their ability to function electrically though, if they're clogged there's no real test for that on the car. Can of berryman's in the tank won't hurt I suppose.

 

Whoa there big fella on the Quick Erase on the ECM codes, those are priceless. Anything in the picture below ring a bell from earlier posts? Take NO Offense, I got out of bed to hit the GMSM... Code 42 rang a bell

 

Ooh, yeah if your car is stuck on base timing it'll be a total dog. Verify you've got the EST wire connected, then hit it with a timing light. You should see like 12-15 degrees at idle, jumping around from time to time, and more when you rev it.

 

Good thing I remembered it then I suppose, thank you for the photo but I am still a little confused. How does the manual say to proceed from code 42?

 

Here's the troubleshooting guide

 

Thank you, it seems to be intermittent. I will report back when I run it tomorrow as it is getting late.

 

Drove it around more today, couldn't get that code to come back. Likely not a recurring issue imo. I unplugged 3 of the injectors and it ran the same with no change. Only when I unplugged the 4th did it have a noticeable effect on it idling. What can I do to test the wires that signal the injectors to open to make sure they are good and it is an injector problem not a wiring problem.

 

Use a noid light to check signal . It’s batch so I’d suspect injectors are bad .

 

Guess I am deaf, put a screwdriver up to each injector while running and I could feel all of them firing. If they were bad could they still be felt firing?

 

If there plugged you won’t notice a cylinder rpm
drop when unplugged electrically .

 

Would they still fire at all and could I feel them firing with a screwdriver if they were plugged?

 

K&Ns do not kill mafs. I have somewhere around 500K collectively on MAF equipped vehicls running K&Ns. My G35 still has both original MAFs on it and it is a 240K mile car that has had K&Ns half its life.

 

Blocked catalytic converter..
Bad intake manifold gaskets..
Vacuum leaks..
Just a few things I found wrong on mine that all would've contributed to low power.

 

Hi guys,
i'm hoping that somebody can help me with a similar problem, same engine, Firebird in my case. I've learnt a lot from this forum, but I'm getting out of ideas.
The car lacks performance, does 0-60 mph in about 8 seconds. I've linked a video showing a comparison between my car and a identical one I found on YouTube (which is doing the specified 6.5 to 60). Please don't get confused by the different units, my digital dash is showing kph (62 mph = 100 kph)

I've also extensively datalogged using TunerPro. I can't seem to find anything out of the ordinary, only maybe that the MAF is a little bit low from what I've read on here, being at 180 g/s WOT. That said the MAF is already a new one (reman Cardone, the old one showed even less at 170 g/s). Apart from that spark plugs and wires have been changed, new distributor cap, timing set to 6 degrees, new VSS, TV Cable adjusted, new TPS (set to 0.55 at idle, 4.25 at WOT), new cat and muffler.
Does the MAF make that much of a difference? Or is it something completely different, like maybe the injectors?

I am grateful for any hint, thanks.

 

Fuel pressure readings? Low fuel pressure can cause lack of performance, last time the filter was changed?

 

Didn't measure that yet, I'll look into it, thanks. Filter was changed last year.

 

Do a search on ohming the injectors, that will give you an idea on what shape they are in. If they are original they are likely done at this point especially if they are the OE Multecs.

 

Will do, thanks. I suspect they are the original ones, car has done 75k miles.

 

Sorry for the delay, my repair shop didn't have time until now.
So the fuel pressure is good from what I know: 42 psi (2,9 bar) with ignition on and 45 psi (3,1 bar) with the engine running.
The injector resistance seems also to be okay, measured lukewarm, between 16,8 and 17,6 ohms. Obviously there still could be something mechanically wrong with them. BTW I don't think mine are Multec, see the picture below.
Running out of ideas, considering getting new injectors.

 

What rear gears are in these cars?

 

Mine has 3.27 9-bolt.

 

did you check the distributor cap for corrosion? Did you correctly set timing by disconnecting wire? Have you replaced ignition control module? They go bad often. Keep it simple. Doubt a sudden injector problem

 

Did you test them both hot and cold???

 

Just to throw my 2 cents in here and I can't see where you have checked or replaced the ICM in the bottom of the distributor. I may have missed it in the post. This controls the electronic spark advance. I saw someone had a code 42. If the spark is not advancing with engine rpm you will have a noticeable loss in power and the car should run fine at idle and low RPM. If you hook up Tuner Pro I believe it tracks the spark advance and should be upwards of 30 degrees or more as you reach max RPM.

 

@vinny R
I didn't have the code 42, that was the original thread creator. I see spark advance in the TunerPro datalog. Though I'm not sure if it does it properly, I've attached a screenshot (cyan line is the spark advance relative to TDC; SA relative to Pulse Width is about 6 degrees less the whole time)
@george88gta
The distributor cap is new and the timing was set to 6 degrees BTDC with the EST wire disconnected. To be honest with you, there was a lot done since I bought it at the beginning of 2021, and I sadly can't pinpoint when the power loss came. Ironically the car runs a lot better overall since then, but it seems to have lost that "brute" power.
@southbay08
Injectors were measure cold.
---
Just to be on the same page, the ICM is the part pictured below? That wasn't changed yet.

 

yes. They go bad frequently. You have to use the correct grease on them ,I forget which one is best there is a thread about it.

 

Check the injectors when they are hot

 

@george88gta
Good to know, thanks.
I've found a good deal on Standard FJ47s in Germany and let the shop change them. The old ones seem to be original. Car idles even better now. Power is still down though.
When I test drove it, I pushed it pretty hard on the Autobahn, and it threw a code 43. So I think that is in line with what you said. Would change the knock sensor too.

 

(Final) update from my side: knock sensor, ICM and ESC changed out. Car doesn't throw codes anymore at WOT/high rpm.
Measured it (not a dyno, but on the street), and it is close to factory specs. Torque seems a little bit low (about 300 ft-lb). I expected the horsepower also to be slightly higher (222 HP), because of the alu heads, custom intake & exhaust runners, but it doesn't seem to make that much of a difference. The reference weight we used was 3530 lbs (1600 kg) plus about 500 lbs for 2 passengers. I'll weigh the car when I get the chance to get exact numbers, as it can be recalculated afterwards, though it shouldn't be far off.
The curves are pretty smooth, so all in all for a 34 year old car I'm satisfied.

 

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