Hi all,
Hope you can help me. I just bought a 1991 Z-28 Convertable. This is my 4th- 3rd gen car. I love this bodystyle in white/grey leather, so I bought another......always wanted this year 91-92.
Here is my problem,
When the car is cold it runs and idles great. As the car warms up
the motor shakes a little and the idle surges at idle in neutral and crusing at 25-30 MPH. It will idle in gear but it should be smoother. Here is what I have done already: new ISC motor, plugs, wires, K & N air filters, new fuel filter. Checked pressure at idle it is 37PSI. Its a little better.
Good compression 155psi average.
My next course is a fuel pressure reg. adjusted to 45 PSI and a new EGR valve.
No Codes at all.
Any other ideas??
Thanks!

 

Another possibility is a clogging or streaming injector or two. It happened to me at 18K miles. Your Multec injectors could be having a similar issue, or insulation breakdown of the operating coils. A power balance test of the injectors could identify any problems.

Is compression/cylinder leakage within acceptable limits?

 

Thanks Vader,
That sounds like my next move, dirty injectors. I replaced them in my 89GTA years ago. Then it ran perfect. I wonder why my car runs good when cold though. Idle is good when it is cold, why does it change as it warms up?
Maybe as the injectors warm up............
I don't know, at least they are cheaper now than in 1994.
I just get the standard 1-2 all good code on the ses light.
It is almost better / cheaper to replace them than clean them.
What do you think?
Pete
clarkeph

 

I had the same problem with my '91. 4 out of the 8 injectors were siezed so I replaced them all.

 

Thanks,
You guys are right on track, I took it to my local reputable chevy dealer for a $85.00 systems test. I wanted to be sure before I spent $300.00+ and did all the work. They said two injectors were shorting out and the intake was leaking a little water into the engine. I'm not sure I believe the leak thing, but I need to replace the injectors now. What is everybodys opinion of the accel injectors?
They are so cheap at Summit I can't pass them up. $239.95??
for all 8?

I will buy the 21LB for the future 350 I already have.
I just need heads and a better intake set up for it.

The intake is so easy now to get at with the fuel rails off anyway,
I will install new gaskets anyway.

Thanks again,

Pete, clarkeph, El Cajon, CA.

 

I wouldn't do it if I were you. Here's my opinion, they are crap. Do a search on them before you order and count the number of good reviews and the number of bad reviews.

Now for my real life experience. I too fell for the cheap Accel injectors. After about 1500 miles, one injector failed. After replacing that one (I didn't do the whole set because they were fairly new), another one failed. That's when I bought some furd injectors and I doing OK right now.

Scott

 

Good advice Scott,
Checked the archives and many people have had problems with the Accel injectors. I ordered a set of Ford Motorsports injectors from Thunder Racing today. Under $300.00 with 2 day shipping to CA.
btw I have had 3 Mustang GT's (sorry chevy guys) over the years and never had a injector problem with any of them. ( 87 lx vert, 89 gt vert and a heavyly modified 94 gt hardtop)
So the Ford injectors must be better.

All of my 3rd gen's had injector problems except the 89 IROC Z vert I had in 2000-2002. Both My 89GTA's, needed injectors.
I had a 89GTA vert (very rare) and a 89 GTA t-top 5 speed.

Thanks
Pete

 

Be advised you'll probably need some prom tuning done if you're changing the injector size as well.......

 

vernw,
I ordered the stock 19lb injector size, should be no problem at all.
The guys at thunder racing said they should work fine with no mods, they also say the Ford Motorsports injectors are excellent. I looked at the manufacturing rating page and everybody likes TR and gave them a high satisfaction rating.
btw,
How does your car run with all those mod's?
Got any 1/4 mile times? How do you like the superam intake?
Thanks for your advice...
Pete

 

Glad you're using the same injector size, those should be good ones. Hopefully that fixes your problem. If not let us know and we'll try to go from there.

As for how mine runs - GREAT!!! Still have to fine tune the WOT stuff, but been hesitant with a factory 10 bolt and WC T-5. Now I've got the Ford 9" 4.11 in, and my TKO Performance upgraded T-5 just got here yesterday. Hopefully in the next week I can get it installed, start my 500 mile break-in, and be hitting the track in late June!!!

Good Luck on your injector swap, hope it fixes it. While waiting for them, you might tape the fuel pressure guage to your windshield, drive around while watching it, and make sure the pressure isn't dropping for some reason (bad filter, pump, FPR, etc.).......

 

The plenum, runners and fuel rails are out and I have my new Ford (seems strange) injectors from Thunder Racing. I still need to pull the intake and dist. to replace the intake gaskets. I am sure this will fix my problem. I will have the intake hot tanked and of course remove the sensors first. It is really grimey/filthy.
I can't put it back that way.

Tommorow night I will remove the rest, wish I had more time....

I will post some pictures of this car, and my restoration project in the garage. (it's a chevy too)

I am 46 but quite a gearhead....

How bout some photos of your cars??

Thanks
I'll let ya know how it runs.

Pete

 

Car is running great now! No rough idle and no surging.
Got a small oil leak coming from the rear top of motor somewhere.
I looked at the intake seal it seems fine. I may have to do the intake seals all over again. (I ain't a rookie) I don't know what happened. The motor has high oil pressure for 114K, could be leaking at the distributor.

Here's a photo of the car....

sorry it's too big a file to add....

Looks good.