i purchased this 85 stick shift coupe two months ago that had what sounded like a miss. I pulled the plugs all were good except cylinders 2 and 4 were clean but had a glazed look to it like they weren't firing or it was running very rich..
The plugs were NGK platinums electrode is that thin wire kind. swapped plugs to ac delco stock plugs car didn't run any better. Eventually I swapped the cap, rotor, coil and delco wires. Still no improvement. Two codes showing TPS and crank sensor. PO installed huge TB and duct taped the air snorkel. Found a good used stock TB from a Corvette unit installed along with new air snorkel. Check engine lights out but car still runs and feels like a miss. When driving must always have rpms up miss wont allow car to be lugged in lower gears.The TPS came with the TB and I did not do a voltage test on it but no codes showing. I changed the cooland flushed everything and swapped the KNock sensor to drain the block.

Did an ohm test on one good fuel injector and got 16.7, did same to the two injectors where the plugs were glazed over and got 16.7? Looks like coils are fine. I bought a noid light and will check the pulsing tonight.

I'd appreciate any help or direction to go in troubleshooting. It's a Z51 car and I'm doing my best to put her back into good unning order. THanks guys Wardie




Since no codes show I'm at a loss on what to check next? I think putting new wires, plugs cap, rotor and coil wasn't a bad idea and realtively inexpensive but now I'm at the poin where Im not troubleshooting and would be just hrowing money and parts at it. I sure could use some suggestions. I haven't ruled out the fuel injectors but not sure what my nxt step should be.

 

If it's never had new injectors it most likely needs them. Otherwise make sure you are checking spark to each plug and fuel pressure.

 

I pulled the plug on cylinders 2 and 4 and found same glazed over look like plugs were washed clean. Put my spark tester on plug and both are firing.

Even though coils checked out ohm wise I think the two injectors are stuck partially open. Car runs better at higher rpms

 

You've started with the basics. That's good. Proceed to the next easy check. What is your fuel pressure? Check with the engine cold and not running. After the pressure comes up and the pump shuts off does your system maintain pressure?

There is absolutely no need to start replacing injectors based on age. Know if you need to replace them first. Ohming them out (both cold and hot) is a great start. The noid light is fine too. If your fuel pressure holds, I would suggest you get yourself an injector tester and check your injector leak-down. It's an easy check that will immediately tell you if your injectors are working or not. You test the injectors in conjunction with your fuel pressure, and the pressure drop on each at one pulse will let you know what each is doing.

NOTE--> Do you have a Factory Service Manual? If not, buy one IMMEDIATELY!! Not only will it help you save a ton of diagnosis time and money, you won't have to post here and wait for responses. The book is set up to take you through problems like this. Responses here usually never follow the same diagnostic flow as the book....and following that advice can have you chasing all over to find a problem that the book may have taken you to quickly.

(All of the above info I posted is in the book! )

Let us know what you find.

Red--

 

my observation based on plug readings is that cylinders 2 & 4 are a problem with what appears too much fuel all the time. Plugs clean and glazed over. Will check FP pressure but two days ago I would her up to redline in 2nd and 3rd gear and she pulled strong just that dang miss. If I had FP problem wouldn't I have a fuel delivery issue when I'm near redline on revs?

Yes I have FSM and that's where I got the ohm reading info. I called Cole at Fuel Injection Connection and went over everything today step by step on what I saw and have done. He feels 2 & 4 FI's are partially open/clogged. I didn't get the sense he was trying to sell me rather he was trying to troubleshoot the problem.

Car sat for a while through the winter and PO didn't take normal maintenance precautions of fuel stabilizing etc. So I agreed with Cole I probably have an injector problem.

Red thanks so much for responding. This site is exceptional for good info from members.

 

If it was my car, I'd do a compression test. And it's easy to check your "new" TPS to be sure it is adjusted correctly.

Swap your #2 & 4 injectors to different cylinders. Does that change your plug readings?

Don't guess. Do the troubleshooting before you start throwing money at the car.

 

I have an 85 as well. I bought mine last year and it had a lot of the stupid stuff done to it that just makes it run poorly. The unfortunate part of the system is that each symptom can be caused by problems with different systems. The fortunate part is that there is not that many systems and once you understand the function of each, it makes it much easier to start farting around with getting it running well.

First before you buy anything get a fork and ground the aldl port and take a drive to see if it even goes into closed loop. when the ses light blinks fast its in open loop. If it blinks slowly it is in closed loop. There is no sense in changing any parts until you know that.

 

What code is that? Not sure about a crank sensor since I don't think you have one. Do you own a scanner or have access to one? Not a paperclip or code reader. See what the ECM sees. I would check the timing to make sure. How did you set the Min Air Rate and TPS?

What do your injectors look like? They are hard to tell without it being on a bench. I can cut off the bottom half and it will still have the same resistance so they could be crudded up even if the coils are good. Regardless, if they are Multec, I would throw them away, shoot them, burn them, drive over them, etc. They hinder you so that you can only gas up at 100% gas stations. See below pic.

 

Spray a stream of water to each cyl exhaust manifold, if it is not firing it will not burn off. I had an injector plug corroded and it was not firing. Good Luck

 

You can have an injector that ohm's fine, but still doesn't fire, is stuck open, or clogged. I'd follow the advice above w/the water (or a IR temp gun), Hot Rod Roy's advice about doing a quick compression test....and I'd pull the fuel rail, and crank the engine while watching the injectors fire...then you'll know if your injectors are REALLY, working.
Read POST # 18, HERE

 

That seems like a LOT of extra work to find out the same results that doing doing the individual injector pressure drop test would show. If the pressure drops on a single cycle of the injector and stops, it works. If the pressure drops more on one that the other -OR- if the pressure either doesn't drop as much/fails to drop, you have a problem injector. Of course that test won't tell you if a specific injector is leaking slowly (seeping), but an injector leak problem can be determined thought the FP test. Me personally? I'd much rather do the diagnostics first to know exactly what I'm going after before pulling stuff apart all *****-nilly on a hunch...but then, that's just me.

 

"All *****-nilly"

Did you READ the thread that I posted?


Further, does the OP have an injector pulser tool? I'm going to go out on a limb here and bet that he doesn't.


.

 

You betcha Tom, I sure did. I read it and fully understood it. We just hit a fork in the road on our approaches to troubleshooting the OP's problem when I read and referred to this in my reply to your post:

It's not that the OP may not have to go there, he very well "may" have to. But to me, I would rather troubleshoot the problem further to have what I would consider to be a sound reason to pull the top end of the engine apart to get those fuel rails off. Neither of us actually know the OP's technical abilities, and it may very well be in his wheelhouse to be able to remove the top end like it's nothing...but you and I know that's a fair amount of work just to "see" something that can be proven by using a pulse tester.

Does the OP have an injector pule tool? I doubt it as well. But for me, a $25.00 investment in that tool would be worth it to gain the piece of mind of knowing whether or not I had to dig out those fuel rails and injectors.

Our diagnostic approaches are different. Both are effective. We just differ on the roads we take to get to the end result.

 

Thanks to all who replied. If by Pulse do you mean NOID light? I did test FI coils and used a NOID light plugged into FI plug to see that it was pulsing .

I have started pilling the plenum and runners. Bought new injectors will report rsults in a couple of days. Hotter than hell here in NE Ohio

 

For future reference, this an example of what I was referring to:




You hook this up to one injector at a time, bring up fuel pressure, pulse the injector once, and note the drop in pressure. There is a procedure for testing them outlined in the FSM. The noid light just verifies that the injector is getting a pulse, this tool actually fires the injector and lets fuel through.

Hope all goes smooth for you! It's hot as all get out here in Indy to, but with garage A/C and an inside temp of 72º, heat waves to me are what happens on the other side of that door!

Will stay tuned!

 

Well said. I agree. I usually tell people to diagnose more than they want to, like you are encouraging. So I "get it". But I also try to give advice that works for most people/what most people have to work with. Most people don't have an injector pulser. For $25? Heck of a deal on a good tool. So....buy the tool? Or have the fuel rail out in ~30 minutes? The OP can decide now.

 

IF they are multec injectors, the rail should be out and they should be in the landfill. Not sure I would want to buy that tool seeing as how I might not have a use for it and it becomes one of the pieces of unused stuff taking up room, which I have too many of already.