First time poster.

'93 Suburban

Problem1:

About a year ago I replaced my 200k mile motor with a rebuilt one from http://www.powertrainproducts.net/ . They called it a 350 H.O. motor for my application, but I did not get enough information from them about the motor. It was built with an rv cam and the paperwork specifically said to 1. set the base timing at factory specs (zero on the hood sticker) and 2. DO NOT chip the computer on this motor.

With timing at zero I had no power. I have it set now at 12, but I have a somewhat rough idle. Decent power, 11-12 mpgs, no pinging and using 87 octane (regular) gas. I had about 14-15 mpgs before this motor. I have read elsewhere that guys run higher octane when they advance the timing. Is 12 too much? Should I try the higher octane?

Problem2:
This may be related to the timing issue above, but is a more recent issue. Whereas the idle/ gas mileage/ timing prob. has been going on for over a year since the motor install, this one just started a month or so ago.

The motor is hard to start when the motor is cold. I have seen other threads on this; Coolant Temp Sensor, leaking injectors to name a few, but I don't think any of those apply here.

The symptom is that on a cold (sitting overnight) start, I have to apply about 1/4 to 1/2 throttle to get the motor to start. I coughs and sputters for a little under a minute before it smooths out enough for me to let off the gas pedal. Then it will idle, but it will idle low. Normally this should idle up to about 900-1100 rpm during a warm-up before it drops down to about 500rpm. However, once the coughing is done it goes right to the 500rpm range with no warm-up period.

This sounded like a CTS problem to me, but the temp looked good on my scanner compared to outside air temp. I changed the CTS anyway and that made no change.

There are no driveability issues, just cold starting. NO codes.

The leaky injectors made sense too, because I can smell gas throught the K&N filter and get some white exhaust on start up, but the injectors were rebuilt when I dropped in the motor, the spray pattern still looks good.

I have been looking at the IAC and TPS on the scanner and Ohms tested both according to my haynes manual. The IAC shows 150 count on start up and works it way down to about 20 when warmed up at idle. (I am not sure what that means the pintle on the IAC should be doing. Is the high number 150 mean the pintle is retracted or extended?)

Any help would be appreciated.

Oh, and why did they say not to chip the computer?

 

Because they don't know what they are doing and likely it helps protect them against their "warranty". What heads are on the new motor? I would look into some data logging to see what is going on. Any shop can rebuild a motor, but only a small fraction know which parts work best with TBI and what is necessary to tune it properly.

 

Yea, like I said, the heads and the cam are a mystery. Data Logging.... I guess that's where you guys are talking about laptops and .bin files? Sounds like fun (Not), but I am trainable. I will start by reading all the threads today. Thanks for the reply.

 

rv cam is usually listed as small as .420/.430 lift @ 204/214 to .458/.458 @ 218/218

No check engine light tells me something mechanical. have you checked compression or fuel pressure?

 

No, I have not checked compression or fp., but if those were issues wouldn't I have other problems beside hard cold starts?

I am sorry for the delay getting back to you guys, but the whole can of worms involved in data logging has got me rebuilding a laptop now. This is why my garage is full of half finished projects, because one thing leads to another and my ADHD meds are too expensive.

 

not necessarily. worn rings + thin cold oil = hard starts. Low fuel pressure tells me it might be a tired pump.

 

UPDATE:

The hard cold starts were realted to the IAC. The IAC port was blocked with a chunk of foam rubber from the TBI gasket for the K&N intake. I have replaced that damn gasket four times in the past 15 years. the foam rubber deteriorates with the fuel spray/vapor and the p.o.s. falls apart. The gasket should be a hard rubber moulded gasket! I had first suspected the IAC and taken the thing out, cleaned the IAC and checked its operation on my scanner, BUT I didn't inspect the IAC port because I had rebuilt the throttle body only a year ago and I knew it was clean. Anyway, that problem solved.

I have also repaired the motherboard on the old laptop that I had laying around and that is up and running now. Now I can work on the data logging......

Look for an update on that first time attempt in a month or so. Any pointers on data logging would welcome.